Fixed #30581 -- Added support for Meta.constraints validation.

Thanks Simon Charette, Keryn Knight, and Mariusz Felisiak for reviews.

django/contrib/postgres/constraints.py

@@ -1,11 +1,13 @@
 import warnings
 
 from django.contrib.postgres.indexes import OpClass
-from django.db import NotSupportedError
+from django.core.exceptions import ValidationError
+from django.db import DEFAULT_DB_ALIAS, NotSupportedError
 from django.db.backends.ddl_references import Expressions, Statement, Table
 from django.db.models import BaseConstraint, Deferrable, F, Q
-from django.db.models.expressions import ExpressionList
+from django.db.models.expressions import Exists, ExpressionList
 from django.db.models.indexes import IndexExpression
+from django.db.models.lookups import PostgresOperatorLookup
 from django.db.models.sql import Query
 from django.utils.deprecation import RemovedInDjango50Warning
 
@@ -32,6 +34,7 @@ class ExclusionConstraint(BaseConstraint):
         deferrable=None,
         include=None,
         opclasses=(),
+        violation_error_message=None,
     ):
         if index_type and index_type.lower() not in {"gist", "spgist"}:
             raise ValueError(
@@ -78,7 +81,7 @@ class ExclusionConstraint(BaseConstraint):
                 category=RemovedInDjango50Warning,
                 stacklevel=2,
             )
-        super().__init__(name=name)
+        super().__init__(name=name, violation_error_message=violation_error_message)
 
     def _get_expressions(self, schema_editor, query):
         expressions = []
@@ -197,3 +200,44 @@ class ExclusionConstraint(BaseConstraint):
             "" if not self.include else " include=%s" % repr(self.include),
             "" if not self.opclasses else " opclasses=%s" % repr(self.opclasses),
         )
+
+    def validate(self, model, instance, exclude=None, using=DEFAULT_DB_ALIAS):
+        queryset = model._default_manager.using(using)
+        replacement_map = instance._get_field_value_map(
+            meta=model._meta, exclude=exclude
+        )
+        lookups = []
+        for idx, (expression, operator) in enumerate(self.expressions):
+            if isinstance(expression, str):
+                expression = F(expression)
+            if isinstance(expression, F):
+                if exclude and expression.name in exclude:
+                    return
+                rhs_expression = replacement_map.get(expression.name, expression)
+            else:
+                rhs_expression = expression.replace_references(replacement_map)
+                if exclude:
+                    for expr in rhs_expression.flatten():
+                        if isinstance(expr, F) and expr.name in exclude:
+                            return
+            # Remove OpClass because it only has sense during the constraint
+            # creation.
+            if isinstance(expression, OpClass):
+                expression = expression.get_source_expressions()[0]
+            if isinstance(rhs_expression, OpClass):
+                rhs_expression = rhs_expression.get_source_expressions()[0]
+            lookup = PostgresOperatorLookup(lhs=expression, rhs=rhs_expression)
+            lookup.postgres_operator = operator
+            lookups.append(lookup)
+        queryset = queryset.filter(*lookups)
+        model_class_pk = instance._get_pk_val(model._meta)
+        if not instance._state.adding and model_class_pk is not None:
+            queryset = queryset.exclude(pk=model_class_pk)
+        if not self.condition:
+            if queryset.exists():
+                raise ValidationError(self.get_violation_error_message())
+        else:
+            if (self.condition & Exists(queryset.filter(self.condition))).check(
+                replacement_map, using=using
+            ):
+                raise ValidationError(self.get_violation_error_message())

django/db/models/base.py

@@ -28,6 +28,7 @@ from django.db.models import NOT_PROVIDED, ExpressionWrapper, IntegerField, Max,
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.constraints import CheckConstraint, UniqueConstraint
 from django.db.models.deletion import CASCADE, Collector
+from django.db.models.expressions import RawSQL
 from django.db.models.fields.related import (
     ForeignObjectRel,
     OneToOneField,
@@ -1189,6 +1190,16 @@ class Model(metaclass=ModelBase):
             setattr(self, cachename, obj)
         return getattr(self, cachename)
 
+    def _get_field_value_map(self, meta, exclude=None):
+        if exclude is None:
+            exclude = set()
+        meta = meta or self._meta
+        return {
+            field.name: Value(getattr(self, field.attname), field)
+            for field in meta.local_concrete_fields
+            if field.name not in exclude
+        }
+
     def prepare_database_save(self, field):
         if self.pk is None:
             raise ValueError(
@@ -1221,7 +1232,7 @@ class Model(metaclass=ModelBase):
         if errors:
             raise ValidationError(errors)
 
-    def _get_unique_checks(self, exclude=None):
+    def _get_unique_checks(self, exclude=None, include_meta_constraints=False):
         """
         Return a list of checks to perform. Since validate_unique() could be
         called from a ModelForm, some fields may have been excluded; we can't
@@ -1234,13 +1245,15 @@ class Model(metaclass=ModelBase):
         unique_checks = []
 
         unique_togethers = [(self.__class__, self._meta.unique_together)]
+        constraints = []
+        if include_meta_constraints:
             constraints = [(self.__class__, self._meta.total_unique_constraints)]
         for parent_class in self._meta.get_parent_list():
             if parent_class._meta.unique_together:
                 unique_togethers.append(
                     (parent_class, parent_class._meta.unique_together)
                 )
-            if parent_class._meta.total_unique_constraints:
+            if include_meta_constraints and parent_class._meta.total_unique_constraints:
                 constraints.append(
                     (parent_class, parent_class._meta.total_unique_constraints)
                 )
@@ -1251,6 +1264,7 @@ class Model(metaclass=ModelBase):
                     # Add the check if the field isn't excluded.
                     unique_checks.append((model_class, tuple(check)))
 
+        if include_meta_constraints:
             for model_class, model_constraints in constraints:
                 for constraint in model_constraints:
                     if not any(name in exclude for name in constraint.fields):
@@ -1410,10 +1424,35 @@ class Model(metaclass=ModelBase):
                 params=params,
             )
 
-    def full_clean(self, exclude=None, validate_unique=True):
+    def get_constraints(self):
+        constraints = [(self.__class__, self._meta.constraints)]
+        for parent_class in self._meta.get_parent_list():
+            if parent_class._meta.constraints:
+                constraints.append((parent_class, parent_class._meta.constraints))
+        return constraints
+
+    def validate_constraints(self, exclude=None):
+        constraints = self.get_constraints()
+        using = router.db_for_write(self.__class__, instance=self)
+
+        errors = {}
+        for model_class, model_constraints in constraints:
+            for constraint in model_constraints:
+                try:
+                    constraint.validate(model_class, self, exclude=exclude, using=using)
+                except ValidationError as e:
+                    if e.code == "unique" and len(constraint.fields) == 1:
+                        errors.setdefault(constraint.fields[0], []).append(e)
+                    else:
+                        errors = e.update_error_dict(errors)
+        if errors:
+            raise ValidationError(errors)
+
+    def full_clean(self, exclude=None, validate_unique=True, validate_constraints=True):
         """
-        Call clean_fields(), clean(), and validate_unique() on the model.
+        Call clean_fields(), clean(), validate_unique(), and
-        Raise a ValidationError for any errors that occur.
+        validate_constraints() on the model. Raise a ValidationError for any
+        errors that occur.
         """
         errors = {}
         if exclude is None:
@@ -1443,6 +1482,16 @@ class Model(metaclass=ModelBase):
             except ValidationError as e:
                 errors = e.update_error_dict(errors)
 
+        # Run constraints checks, but only for fields that passed validation.
+        if validate_constraints:
+            for name in errors:
+                if name != NON_FIELD_ERRORS and name not in exclude:
+                    exclude.add(name)
+            try:
+                self.validate_constraints(exclude=exclude)
+            except ValidationError as e:
+                errors = e.update_error_dict(errors)
+
         if errors:
             raise ValidationError(errors)
 
@@ -2339,8 +2388,28 @@ class Model(metaclass=ModelBase):
                         connection.features.supports_table_check_constraints
                         or "supports_table_check_constraints"
                         not in cls._meta.required_db_features
-                    ) and isinstance(constraint.check, Q):
+                    ):
-                        references.update(cls._get_expr_references(constraint.check))
+                        if isinstance(constraint.check, Q):
+                            references.update(
+                                cls._get_expr_references(constraint.check)
+                            )
+                        if any(
+                            isinstance(expr, RawSQL)
+                            for expr in constraint.check.flatten()
+                        ):
+                            errors.append(
+                                checks.Warning(
+                                    f"Check constraint {constraint.name!r} contains "
+                                    f"RawSQL() expression and won't be validated "
+                                    f"during the model full_clean().",
+                                    hint=(
+                                        "Silence this warning if you don't care about "
+                                        "it."
+                                    ),
+                                    obj=cls,
+                                    id="models.W045",
+                                ),
+                            )
             for field_name, *lookups in references:
                 # pk is an alias that won't be found by opts.get_field.
                 if field_name != "pk":

django/db/models/constraints.py

@@ -1,16 +1,25 @@
 from enum import Enum
 
-from django.db.models.expressions import ExpressionList, F
+from django.core.exceptions import FieldError, ValidationError
+from django.db import connections
+from django.db.models.expressions import Exists, ExpressionList, F
 from django.db.models.indexes import IndexExpression
+from django.db.models.lookups import Exact
 from django.db.models.query_utils import Q
 from django.db.models.sql.query import Query
+from django.db.utils import DEFAULT_DB_ALIAS
+from django.utils.translation import gettext_lazy as _
 
 __all__ = ["BaseConstraint", "CheckConstraint", "Deferrable", "UniqueConstraint"]
 
 
 class BaseConstraint:
-    def __init__(self, name):
+    violation_error_message = _("Constraint “%(name)s” is violated.")
+
+    def __init__(self, name, violation_error_message=None):
         self.name = name
+        if violation_error_message is not None:
+            self.violation_error_message = violation_error_message
 
     @property
     def contains_expressions(self):
@@ -25,6 +34,12 @@ class BaseConstraint:
     def remove_sql(self, model, schema_editor):
         raise NotImplementedError("This method must be implemented by a subclass.")
 
+    def validate(self, model, instance, exclude=None, using=DEFAULT_DB_ALIAS):
+        raise NotImplementedError("This method must be implemented by a subclass.")
+
+    def get_violation_error_message(self):
+        return self.violation_error_message % {"name": self.name}
+
     def deconstruct(self):
         path = "%s.%s" % (self.__class__.__module__, self.__class__.__name__)
         path = path.replace("django.db.models.constraints", "django.db.models")
@@ -36,13 +51,13 @@ class BaseConstraint:
 
 
 class CheckConstraint(BaseConstraint):
-    def __init__(self, *, check, name):
+    def __init__(self, *, check, name, violation_error_message=None):
         self.check = check
         if not getattr(check, "conditional", False):
             raise TypeError(
                 "CheckConstraint.check must be a Q instance or boolean expression."
             )
-        super().__init__(name)
+        super().__init__(name, violation_error_message=violation_error_message)
 
     def _get_check_sql(self, model, schema_editor):
         query = Query(model=model, alias_cols=False)
@@ -62,6 +77,14 @@ class CheckConstraint(BaseConstraint):
     def remove_sql(self, model, schema_editor):
         return schema_editor._delete_check_sql(model, self.name)
 
+    def validate(self, model, instance, exclude=None, using=DEFAULT_DB_ALIAS):
+        against = instance._get_field_value_map(meta=model._meta, exclude=exclude)
+        try:
+            if not Q(self.check).check(against, using=using):
+                raise ValidationError(self.get_violation_error_message())
+        except FieldError:
+            pass
+
     def __repr__(self):
         return "<%s: check=%s name=%s>" % (
             self.__class__.__qualname__,
@@ -99,6 +122,7 @@ class UniqueConstraint(BaseConstraint):
         deferrable=None,
         include=None,
         opclasses=(),
+        violation_error_message=None,
     ):
         if not name:
             raise ValueError("A unique constraint must be named.")
@@ -148,7 +172,7 @@ class UniqueConstraint(BaseConstraint):
             F(expression) if isinstance(expression, str) else expression
             for expression in expressions
         )
-        super().__init__(name)
+        super().__init__(name, violation_error_message=violation_error_message)
 
     @property
     def contains_expressions(self):
@@ -265,3 +289,61 @@ class UniqueConstraint(BaseConstraint):
         if self.opclasses:
             kwargs["opclasses"] = self.opclasses
         return path, self.expressions, kwargs
+
+    def validate(self, model, instance, exclude=None, using=DEFAULT_DB_ALIAS):
+        queryset = model._default_manager.using(using)
+        if self.fields:
+            lookup_kwargs = {}
+            for field_name in self.fields:
+                if exclude and field_name in exclude:
+                    return
+                field = model._meta.get_field(field_name)
+                lookup_value = getattr(instance, field.attname)
+                if lookup_value is None or (
+                    lookup_value == ""
+                    and connections[using].features.interprets_empty_strings_as_nulls
+                ):
+                    # A composite constraint containing NULL value cannot cause
+                    # a violation since NULL != NULL in SQL.
+                    return
+                lookup_kwargs[field.name] = lookup_value
+            queryset = queryset.filter(**lookup_kwargs)
+        else:
+            # Ignore constraints with excluded fields.
+            if exclude:
+                for expression in self.expressions:
+                    for expr in expression.flatten():
+                        if isinstance(expr, F) and expr.name in exclude:
+                            return
+            replacement_map = instance._get_field_value_map(
+                meta=model._meta, exclude=exclude
+            )
+            expressions = [
+                Exact(expr, expr.replace_references(replacement_map))
+                for expr in self.expressions
+            ]
+            queryset = queryset.filter(*expressions)
+        model_class_pk = instance._get_pk_val(model._meta)
+        if not instance._state.adding and model_class_pk is not None:
+            queryset = queryset.exclude(pk=model_class_pk)
+        if not self.condition:
+            if queryset.exists():
+                if self.expressions:
+                    raise ValidationError(self.get_violation_error_message())
+                # When fields are defined, use the unique_error_message() for
+                # backward compatibility.
+                for model, constraints in instance.get_constraints():
+                    for constraint in constraints:
+                        if constraint is self:
+                            raise ValidationError(
+                                instance.unique_error_message(model, self.fields)
+                            )
+        else:
+            against = instance._get_field_value_map(meta=model._meta, exclude=exclude)
+            try:
+                if (self.condition & Exists(queryset.filter(self.condition))).check(
+                    against, using=using
+                ):
+                    raise ValidationError(self.get_violation_error_message())
+            except FieldError:
+                pass

django/db/models/expressions.py

@@ -387,6 +387,18 @@ class BaseExpression:
         )
         return clone
 
+    def replace_references(self, references_map):
+        clone = self.copy()
+        clone.set_source_expressions(
+            [
+                references_map.get(expr.name, expr)
+                if isinstance(expr, F)
+                else expr.replace_references(references_map)
+                for expr in self.get_source_expressions()
+            ]
+        )
+        return clone
+
     def copy(self):
         return copy.copy(self)
 

django/forms/models.py

@@ -806,7 +806,8 @@ class BaseModelFormSet(BaseFormSet):
         for form in valid_forms:
             exclude = form._get_validation_exclusions()
             unique_checks, date_checks = form.instance._get_unique_checks(
-                exclude=exclude
+                exclude=exclude,
+                include_meta_constraints=True,
             )
             all_unique_checks.update(unique_checks)
             all_date_checks.update(date_checks)

docs/ref/checks.txt

@@ -395,6 +395,8 @@ Models
 * **models.W043**: ``<database>`` does not support indexes on expressions.
 * **models.W044**: ``<database>`` does not support unique constraints on
   expressions.
+* **models.W045**: Check constraint ``<constraint>`` contains ``RawSQL()``
+  expression and won't be validated during the model ``full_clean()``.
 
 Security
 --------

docs/ref/contrib/postgres/constraints.txt

@@ -12,7 +12,7 @@ PostgreSQL supports additional data integrity constraints available from the
 ``ExclusionConstraint``
 =======================
 
-.. class:: ExclusionConstraint(*, name, expressions, index_type=None, condition=None, deferrable=None, include=None, opclasses=())
+.. class:: ExclusionConstraint(*, name, expressions, index_type=None, condition=None, deferrable=None, include=None, opclasses=(), violation_error_message=None)
 
     Creates an exclusion constraint in the database. Internally, PostgreSQL
     implements exclusion constraints using indexes. The default index type is
@@ -27,6 +27,14 @@ PostgreSQL supports additional data integrity constraints available from the
     :exc:`~django.db.IntegrityError` is raised. Similarly, when update
     conflicts with an existing row.
 
+    Exclusion constraints are checked during the :ref:`model validation
+    <validating-objects>`.
+
+    .. versionchanged:: 4.1
+
+        In older versions, exclusion constraints were not checked during model
+        validation.
+
 ``name``
 --------
 
@@ -165,6 +173,15 @@ creates an exclusion constraint on ``circle`` using ``circle_ops``.
     :class:`OpClass() <django.contrib.postgres.indexes.OpClass>` in
     :attr:`~ExclusionConstraint.expressions`.
 
+``violation_error_message``
+---------------------------
+
+.. versionadded:: 4.1
+
+The error message used when ``ValidationError`` is raised during
+:ref:`model validation <validating-objects>`. Defaults to
+:attr:`.BaseConstraint.violation_error_message`.
+
 Examples
 --------
 

docs/ref/models/constraints.txt

@@ -31,24 +31,21 @@ option.
 
 .. admonition:: Validation of Constraints
 
-    In general constraints are **not** checked during ``full_clean()``, and do
+    Constraints are checked during the :ref:`model validation
-    not raise ``ValidationError``\s. Rather you'll get a database integrity
+    <validating-objects>`.
-    error on ``save()``. ``UniqueConstraint``\s without a
+
-    :attr:`~UniqueConstraint.condition` (i.e. non-partial unique constraints)
+.. versionchanged:: 4.1
-    and :attr:`~UniqueConstraint.expressions` (i.e. non-functional unique
+
-    constraints) are different in this regard, in that they leverage the
+    In older versions, constraints were not checked during model validation.
-    existing ``validate_unique()`` logic, and thus enable two-stage validation.
-    In addition to ``IntegrityError`` on ``save()``, ``ValidationError`` is
-    also raised during model validation when the ``UniqueConstraint`` is
-    violated.
 
 ``BaseConstraint``
 ==================
 
-.. class:: BaseConstraint(name)
+.. class:: BaseConstraint(name, violation_error_message=None)
 
     Base class for all constraints. Subclasses must implement
-    ``constraint_sql()``, ``create_sql()``, and ``remove_sql()`` methods.
+    ``constraint_sql()``, ``create_sql()``, ``remove_sql()`` and
+    ``validate()`` methods.
 
 All constraints have the following parameters in common:
 
@@ -60,10 +57,37 @@ All constraints have the following parameters in common:
 The name of the constraint. You must always specify a unique name for the
 constraint.
 
+``violation_error_message``
+---------------------------
+
+.. versionadded:: 4.1
+
+.. attribute:: BaseConstraint.violation_error_message
+
+The error message used when ``ValidationError`` is raised during
+:ref:`model validation <validating-objects>`. Defaults to
+``"Constraint “%(name)s” is violated."``.
+
+``validate()``
+--------------
+
+.. versionadded:: 4.1
+
+.. method:: BaseConstraint.validate(model, instance, exclude=None, using=DEFAULT_DB_ALIAS)
+
+Validates that the constraint, defined on ``model``, is respected on the
+``instance``. This will do a query on the database to ensure that the
+constraint is respected. If fields in the ``exclude`` list are needed to
+validate the constraint, the constraint is ignored.
+
+Raise a ``ValidationError`` if the constraint is violated.
+
+This method must be implemented by a subclass.
+
 ``CheckConstraint``
 ===================
 
-.. class:: CheckConstraint(*, check, name)
+.. class:: CheckConstraint(*, check, name, violation_error_message=None)
 
     Creates a check constraint in the database.
 
@@ -78,10 +102,14 @@ specifies the check you want the constraint to enforce.
 For example, ``CheckConstraint(check=Q(age__gte=18), name='age_gte_18')``
 ensures the age field is never less than 18.
 
+.. versionchanged:: 4.1
+
+    The ``violation_error_message`` argument was added.
+
 ``UniqueConstraint``
 ====================
 
-.. class:: UniqueConstraint(*expressions, fields=(), name=None, condition=None, deferrable=None, include=None, opclasses=())
+.. class:: UniqueConstraint(*expressions, fields=(), name=None, condition=None, deferrable=None, include=None, opclasses=(), violation_error_message=None)
 
     Creates a unique constraint in the database.
 
@@ -203,3 +231,21 @@ For example::
 creates a unique index on ``username`` using ``varchar_pattern_ops``.
 
 ``opclasses`` are ignored for databases besides PostgreSQL.
+
+``violation_error_message``
+---------------------------
+
+.. versionadded:: 4.1
+
+.. attribute:: UniqueConstraint.violation_error_message
+
+The error message used when ``ValidationError`` is raised during
+:ref:`model validation <validating-objects>`. Defaults to
+:attr:`.BaseConstraint.violation_error_message`.
+
+This message is *not used* for :class:`UniqueConstraint`\s with
+:attr:`~UniqueConstraint.fields` and without a
+:attr:`~UniqueConstraint.condition`. Such :class:`~UniqueConstraint`\s show the
+same message as constraints defined with
+:attr:`.Field.unique` or in
+:attr:`Meta.unique_together <django.db.models.Options.constraints>`.

docs/ref/models/instances.txt

@@ -198,9 +198,10 @@ There are three steps involved in validating a model:
 1. Validate the model fields - :meth:`Model.clean_fields()`
 2. Validate the model as a whole - :meth:`Model.clean()`
 3. Validate the field uniqueness - :meth:`Model.validate_unique()`
+4. Validate the constraints - :meth:`Model.validate_constraints`
 
-All three steps are performed when you call a model's
+All four steps are performed when you call a model's :meth:`~Model.full_clean`
-:meth:`~Model.full_clean()` method.
+method.
 
 When you use a :class:`~django.forms.ModelForm`, the call to
 :meth:`~django.forms.Form.is_valid()` will perform these validation steps for
@@ -210,12 +211,18 @@ need to call a model's :meth:`~Model.full_clean()` method if you plan to handle
 validation errors yourself, or if you have excluded fields from the
 :class:`~django.forms.ModelForm` that require validation.
 
-.. method:: Model.full_clean(exclude=None, validate_unique=True)
+.. versionchanged:: 4.1
 
-This method calls :meth:`Model.clean_fields()`, :meth:`Model.clean()`, and
+    In older versions, constraints were not checked during the model
-:meth:`Model.validate_unique()` (if ``validate_unique`` is ``True``), in that
+    validation.
-order and raises a :exc:`~django.core.exceptions.ValidationError` that has a
+
-``message_dict`` attribute containing errors from all three stages.
+.. method:: Model.full_clean(exclude=None, validate_unique=True, validate_constraints=True)
+
+This method calls :meth:`Model.clean_fields()`, :meth:`Model.clean()`,
+:meth:`Model.validate_unique()` (if ``validate_unique`` is ``True``),  and
+:meth:`Model.validate_constraints()` (if ``validate_constraints`` is ``True``)
+in that order and raises a :exc:`~django.core.exceptions.ValidationError` that
+has a ``message_dict`` attribute containing errors from all four stages.
 
 The optional ``exclude`` argument can be used to provide a list of field names
 that can be excluded from validation and cleaning.
@@ -238,6 +245,10 @@ models. For example::
 
 The first step ``full_clean()`` performs is to clean each individual field.
 
+.. versionchanged:: 4.1
+
+    The ``validate_constraints`` argument was added.
+
 .. method:: Model.clean_fields(exclude=None)
 
 This method will validate all fields on your model. The optional ``exclude``
@@ -306,7 +317,7 @@ pass a dictionary mapping field names to errors::
         'pub_date': ValidationError(_('Invalid date.'), code='invalid'),
     })
 
-Finally, ``full_clean()`` will check any unique constraints on your model.
+Then, ``full_clean()`` will check unique constraints on your model.
 
 .. admonition:: How to raise field-specific validation errors if those fields don't appear in a ``ModelForm``
 
@@ -339,16 +350,40 @@ Finally, ``full_clean()`` will check any unique constraints on your model.
 
 .. method:: Model.validate_unique(exclude=None)
 
-This method is similar to :meth:`~Model.clean_fields`, but validates all
+This method is similar to :meth:`~Model.clean_fields`, but validates
-uniqueness constraints on your model instead of individual field values. The
+uniqueness constraints defined via :attr:`.Field.unique`,
-optional ``exclude`` argument allows you to provide a list of field names to
+:attr:`.Field.unique_for_date`, :attr:`.Field.unique_for_month`,
-exclude from validation. It will raise a
+:attr:`.Field.unique_for_year`, or :attr:`Meta.unique_together
+<django.db.models.Options.unique_together>` on your model instead of individual
+field values. The optional ``exclude`` argument allows you to provide a list of
+field names to exclude from validation. It will raise a
 :exc:`~django.core.exceptions.ValidationError` if any fields fail validation.
 
+:class:`~django.db.models.UniqueConstraint`\s defined in the
+:attr:`Meta.constraints <django.db.models.Options.constraints>` are validated
+by :meth:`Model.validate_constraints`.
+
 Note that if you provide an ``exclude`` argument to ``validate_unique()``, any
 :attr:`~django.db.models.Options.unique_together` constraint involving one of
 the fields you provided will not be checked.
 
+Finally, ``full_clean()`` will check any other constraints on your model.
+
+.. versionchanged:: 4.1
+
+    In older versions, :class:`~django.db.models.UniqueConstraint`\s were
+    validated by ``validate_unique()``.
+
+.. method:: Model.validate_constraints(exclude=None)
+
+.. versionadded:: 4.1
+
+This method validates all constraints defined in
+:attr:`Meta.constraints <django.db.models.Options.constraints>`. The
+optional ``exclude`` argument allows you to provide a list of field names to
+exclude from validation. It will raise a
+:exc:`~django.core.exceptions.ValidationError` if any constraints fail
+validation.
 
 Saving objects
 ==============

docs/releases/4.1.txt

@@ -65,6 +65,15 @@ advantage of developments in the ORM's asynchronous support as it evolves.
 
 See :ref:`async-queries` for details and limitations.
 
+Validation of Constraints
+-------------------------
+
+:class:`Check <django.db.models.CheckConstraint>`,
+:class:`unique <django.db.models.UniqueConstraint>`, and :class:`exclusion
+<django.contrib.postgres.constraints.ExclusionConstraint>` constraints defined
+in the :attr:`Meta.constraints <django.db.models.Options.constraints>` option
+are now checked during :ref:`model validation <validating-objects>`.
+
 .. _csrf-cookie-masked-usage:
 
 ``CSRF_COOKIE_MASKED`` setting
@@ -551,6 +560,10 @@ Miscellaneous
 * The undocumented ``django.contrib.auth.views.SuccessURLAllowedHostsMixin``
   mixin is replaced by ``RedirectURLMixin``.
 
+* :class:`~django.db.models.BaseConstraint` subclasses must implement
+  :meth:`~django.db.models.BaseConstraint.validate` method to allow those
+  constraints to be used for validation.
+
 .. _deprecated-features-4.1:
 
 Features deprecated in 4.1

tests/constraints/models.py

@@ -38,6 +38,10 @@ class UniqueConstraintProduct(models.Model):
         ]
 
 
+class ChildUniqueConstraintProduct(UniqueConstraintProduct):
+    pass
+
+
 class UniqueConstraintConditionProduct(models.Model):
     name = models.CharField(max_length=255)
     color = models.CharField(max_length=32, null=True)

tests/constraints/tests.py

@@ -10,6 +10,7 @@ from django.test import SimpleTestCase, TestCase, skipUnlessDBFeature
 
 from .models import (
     ChildModel,
+    ChildUniqueConstraintProduct,
     Product,
     UniqueConstraintConditionProduct,
     UniqueConstraintDeferrable,
@@ -46,6 +47,24 @@ class BaseConstraintTests(SimpleTestCase):
         with self.assertRaisesMessage(NotImplementedError, msg):
             c.remove_sql(None, None)
 
+    def test_validate(self):
+        c = BaseConstraint("name")
+        msg = "This method must be implemented by a subclass."
+        with self.assertRaisesMessage(NotImplementedError, msg):
+            c.validate(None, None)
+
+    def test_default_violation_error_message(self):
+        c = BaseConstraint("name")
+        self.assertEqual(
+            c.get_violation_error_message(), "Constraint “name” is violated."
+        )
+
+    def test_custom_violation_error_message(self):
+        c = BaseConstraint(
+            "base_name", violation_error_message="custom %(name)s message"
+        )
+        self.assertEqual(c.get_violation_error_message(), "custom base_name message")
+
 
 class CheckConstraintTests(TestCase):
     def test_eq(self):
@@ -122,16 +141,60 @@ class CheckConstraintTests(TestCase):
         constraints = get_constraints(ChildModel._meta.db_table)
         self.assertIn("constraints_childmodel_adult", constraints)
 
+    def test_validate(self):
+        check = models.Q(price__gt=models.F("discounted_price"))
+        constraint = models.CheckConstraint(check=check, name="price")
+        # Invalid product.
+        invalid_product = Product(price=10, discounted_price=42)
+        with self.assertRaises(ValidationError):
+            constraint.validate(Product, invalid_product)
+        with self.assertRaises(ValidationError):
+            constraint.validate(Product, invalid_product, exclude={"unit"})
+        # Fields used by the check constraint are excluded.
+        constraint.validate(Product, invalid_product, exclude={"price"})
+        constraint.validate(Product, invalid_product, exclude={"discounted_price"})
+        constraint.validate(
+            Product,
+            invalid_product,
+            exclude={"discounted_price", "price"},
+        )
+        # Valid product.
+        constraint.validate(Product, Product(price=10, discounted_price=5))
+
+    def test_validate_boolean_expressions(self):
+        constraint = models.CheckConstraint(
+            check=models.expressions.ExpressionWrapper(
+                models.Q(price__gt=500) | models.Q(price__lt=500),
+                output_field=models.BooleanField(),
+            ),
+            name="price_neq_500_wrap",
+        )
+        msg = f"Constraint “{constraint.name}” is violated."
+        with self.assertRaisesMessage(ValidationError, msg):
+            constraint.validate(Product, Product(price=500, discounted_price=5))
+        constraint.validate(Product, Product(price=501, discounted_price=5))
+        constraint.validate(Product, Product(price=499, discounted_price=5))
+
+    def test_validate_rawsql_expressions_noop(self):
+        constraint = models.CheckConstraint(
+            check=models.expressions.RawSQL(
+                "price < %s OR price > %s",
+                (500, 500),
+                output_field=models.BooleanField(),
+            ),
+            name="price_neq_500_raw",
+        )
+        # RawSQL can not be checked and is always considered valid.
+        constraint.validate(Product, Product(price=500, discounted_price=5))
+        constraint.validate(Product, Product(price=501, discounted_price=5))
+        constraint.validate(Product, Product(price=499, discounted_price=5))
+
 
 class UniqueConstraintTests(TestCase):
     @classmethod
     def setUpTestData(cls):
-        cls.p1, cls.p2 = UniqueConstraintProduct.objects.bulk_create(
+        cls.p1 = UniqueConstraintProduct.objects.create(name="p1", color="red")
-            [
+        cls.p2 = UniqueConstraintProduct.objects.create(name="p2")
-                UniqueConstraintProduct(name="p1", color="red"),
-                UniqueConstraintProduct(name="p2"),
-            ]
-        )
 
     def test_eq(self):
         self.assertEqual(
@@ -415,15 +478,135 @@ class UniqueConstraintTests(TestCase):
         with self.assertRaisesMessage(ValidationError, msg):
             UniqueConstraintProduct(
                 name=self.p1.name, color=self.p1.color
-            ).validate_unique()
+            ).validate_constraints()
 
     @skipUnlessDBFeature("supports_partial_indexes")
     def test_model_validation_with_condition(self):
-        """Partial unique constraints are ignored by Model.validate_unique()."""
+        """
+        Partial unique constraints are not ignored by
+        Model.validate_constraints().
+        """
         obj1 = UniqueConstraintConditionProduct.objects.create(name="p1", color="red")
         obj2 = UniqueConstraintConditionProduct.objects.create(name="p2")
-        UniqueConstraintConditionProduct(name=obj1.name, color="blue").validate_unique()
+        UniqueConstraintConditionProduct(
-        UniqueConstraintConditionProduct(name=obj2.name).validate_unique()
+            name=obj1.name, color="blue"
+        ).validate_constraints()
+        msg = "Constraint “name_without_color_uniq” is violated."
+        with self.assertRaisesMessage(ValidationError, msg):
+            UniqueConstraintConditionProduct(name=obj2.name).validate_constraints()
+
+    def test_validate(self):
+        constraint = UniqueConstraintProduct._meta.constraints[0]
+        msg = "Unique constraint product with this Name and Color already exists."
+        non_unique_product = UniqueConstraintProduct(
+            name=self.p1.name, color=self.p1.color
+        )
+        with self.assertRaisesMessage(ValidationError, msg):
+            constraint.validate(UniqueConstraintProduct, non_unique_product)
+        # Null values are ignored.
+        constraint.validate(
+            UniqueConstraintProduct,
+            UniqueConstraintProduct(name=self.p2.name, color=None),
+        )
+        # Existing instances have their existing row excluded.
+        constraint.validate(UniqueConstraintProduct, self.p1)
+        # Unique fields are excluded.
+        constraint.validate(
+            UniqueConstraintProduct,
+            non_unique_product,
+            exclude={"name"},
+        )
+        constraint.validate(
+            UniqueConstraintProduct,
+            non_unique_product,
+            exclude={"color"},
+        )
+        constraint.validate(
+            UniqueConstraintProduct,
+            non_unique_product,
+            exclude={"name", "color"},
+        )
+        # Validation on a child instance.
+        with self.assertRaisesMessage(ValidationError, msg):
+            constraint.validate(
+                UniqueConstraintProduct,
+                ChildUniqueConstraintProduct(name=self.p1.name, color=self.p1.color),
+            )
+
+    @skipUnlessDBFeature("supports_partial_indexes")
+    def test_validate_condition(self):
+        p1 = UniqueConstraintConditionProduct.objects.create(name="p1")
+        constraint = UniqueConstraintConditionProduct._meta.constraints[0]
+        msg = "Constraint “name_without_color_uniq” is violated."
+        with self.assertRaisesMessage(ValidationError, msg):
+            constraint.validate(
+                UniqueConstraintConditionProduct,
+                UniqueConstraintConditionProduct(name=p1.name, color=None),
+            )
+        # Values not matching condition are ignored.
+        constraint.validate(
+            UniqueConstraintConditionProduct,
+            UniqueConstraintConditionProduct(name=p1.name, color="anything-but-none"),
+        )
+        # Existing instances have their existing row excluded.
+        constraint.validate(UniqueConstraintConditionProduct, p1)
+        # Unique field is excluded.
+        constraint.validate(
+            UniqueConstraintConditionProduct,
+            UniqueConstraintConditionProduct(name=p1.name, color=None),
+            exclude={"name"},
+        )
+
+    def test_validate_expression(self):
+        constraint = models.UniqueConstraint(Lower("name"), name="name_lower_uniq")
+        msg = "Constraint “name_lower_uniq” is violated."
+        with self.assertRaisesMessage(ValidationError, msg):
+            constraint.validate(
+                UniqueConstraintProduct,
+                UniqueConstraintProduct(name=self.p1.name.upper()),
+            )
+        constraint.validate(
+            UniqueConstraintProduct,
+            UniqueConstraintProduct(name="another-name"),
+        )
+        # Existing instances have their existing row excluded.
+        constraint.validate(UniqueConstraintProduct, self.p1)
+        # Unique field is excluded.
+        constraint.validate(
+            UniqueConstraintProduct,
+            UniqueConstraintProduct(name=self.p1.name.upper()),
+            exclude={"name"},
+        )
+
+    def test_validate_expression_condition(self):
+        constraint = models.UniqueConstraint(
+            Lower("name"),
+            name="name_lower_without_color_uniq",
+            condition=models.Q(color__isnull=True),
+        )
+        non_unique_product = UniqueConstraintProduct(name=self.p2.name.upper())
+        msg = "Constraint “name_lower_without_color_uniq” is violated."
+        with self.assertRaisesMessage(ValidationError, msg):
+            constraint.validate(UniqueConstraintProduct, non_unique_product)
+        # Values not matching condition are ignored.
+        constraint.validate(
+            UniqueConstraintProduct,
+            UniqueConstraintProduct(name=self.p1.name, color=self.p1.color),
+        )
+        # Existing instances have their existing row excluded.
+        constraint.validate(UniqueConstraintProduct, self.p2)
+        # Unique field is excluded.
+        constraint.validate(
+            UniqueConstraintProduct,
+            non_unique_product,
+            exclude={"name"},
+        )
+        # Field from a condition is excluded.
+        constraint.validate(
+            UniqueConstraintProduct,
+            non_unique_product,
+            exclude={"color"},
+        )
 
     def test_name(self):
         constraints = get_constraints(UniqueConstraintProduct._meta.db_table)

tests/invalid_models_tests/test_models.py

@@ -2198,6 +2198,66 @@ class ConstraintsTests(TestCase):
         ]
         self.assertCountEqual(errors, expected_errors)
 
+    def test_check_constraint_raw_sql_check(self):
+        class Model(models.Model):
+            class Meta:
+                required_db_features = {"supports_table_check_constraints"}
+                constraints = [
+                    models.CheckConstraint(check=models.Q(id__gt=0), name="q_check"),
+                    models.CheckConstraint(
+                        check=models.ExpressionWrapper(
+                            models.Q(price__gt=20),
+                            output_field=models.BooleanField(),
+                        ),
+                        name="expression_wrapper_check",
+                    ),
+                    models.CheckConstraint(
+                        check=models.expressions.RawSQL(
+                            "id = 0",
+                            params=(),
+                            output_field=models.BooleanField(),
+                        ),
+                        name="raw_sql_check",
+                    ),
+                    models.CheckConstraint(
+                        check=models.Q(
+                            models.ExpressionWrapper(
+                                models.Q(
+                                    models.expressions.RawSQL(
+                                        "id = 0",
+                                        params=(),
+                                        output_field=models.BooleanField(),
+                                    )
+                                ),
+                                output_field=models.BooleanField(),
+                            )
+                        ),
+                        name="nested_raw_sql_check",
+                    ),
+                ]
+
+        expected_warnings = (
+            [
+                Warning(
+                    "Check constraint 'raw_sql_check' contains RawSQL() expression and "
+                    "won't be validated during the model full_clean().",
+                    hint="Silence this warning if you don't care about it.",
+                    obj=Model,
+                    id="models.W045",
+                ),
+                Warning(
+                    "Check constraint 'nested_raw_sql_check' contains RawSQL() "
+                    "expression and won't be validated during the model full_clean().",
+                    hint="Silence this warning if you don't care about it.",
+                    obj=Model,
+                    id="models.W045",
+                ),
+            ]
+            if connection.features.supports_table_check_constraints
+            else []
+        )
+        self.assertEqual(Model.check(databases=self.databases), expected_warnings)
+
     def test_unique_constraint_with_condition(self):
         class Model(models.Model):
             age = models.IntegerField()

tests/postgres_tests/test_constraints.py

@@ -2,6 +2,7 @@ import datetime
 from unittest import mock
 
 from django.contrib.postgres.indexes import OpClass
+from django.core.exceptions import ValidationError
 from django.db import IntegrityError, NotSupportedError, connection, transaction
 from django.db.models import (
     CheckConstraint,
@@ -612,18 +613,26 @@ class ExclusionConstraintTests(PostgreSQLTestCase):
             timezone.datetime(2018, 6, 28),
             timezone.datetime(2018, 6, 29),
         ]
-        HotelReservation.objects.create(
+        reservation = HotelReservation.objects.create(
             datespan=DateRange(datetimes[0].date(), datetimes[1].date()),
             start=datetimes[0],
             end=datetimes[1],
             room=room102,
         )
+        constraint.validate(HotelReservation, reservation)
         HotelReservation.objects.create(
             datespan=DateRange(datetimes[1].date(), datetimes[3].date()),
             start=datetimes[1],
             end=datetimes[3],
             room=room102,
         )
+        HotelReservation.objects.create(
+            datespan=DateRange(datetimes[3].date(), datetimes[4].date()),
+            start=datetimes[3],
+            end=datetimes[4],
+            room=room102,
+            cancelled=True,
+        )
         # Overlap dates.
         with self.assertRaises(IntegrityError), transaction.atomic():
             reservation = HotelReservation(
@@ -632,10 +641,12 @@ class ExclusionConstraintTests(PostgreSQLTestCase):
                 end=datetimes[2],
                 room=room102,
             )
+            msg = f"Constraint “{constraint.name}” is violated."
+            with self.assertRaisesMessage(ValidationError, msg):
+                constraint.validate(HotelReservation, reservation)
             reservation.save()
         # Valid range.
-        HotelReservation.objects.bulk_create(
+        other_valid_reservations = [
-            [
             # Other room.
             HotelReservation(
                 datespan=(datetimes[1].date(), datetimes[2].date()),
@@ -659,6 +670,29 @@ class ExclusionConstraintTests(PostgreSQLTestCase):
                 room=room102,
             ),
         ]
+        for reservation in other_valid_reservations:
+            constraint.validate(HotelReservation, reservation)
+        HotelReservation.objects.bulk_create(other_valid_reservations)
+        # Excluded fields.
+        constraint.validate(
+            HotelReservation,
+            HotelReservation(
+                datespan=(datetimes[1].date(), datetimes[2].date()),
+                start=datetimes[1],
+                end=datetimes[2],
+                room=room102,
+            ),
+            exclude={"room"},
+        )
+        constraint.validate(
+            HotelReservation,
+            HotelReservation(
+                datespan=(datetimes[1].date(), datetimes[2].date()),
+                start=datetimes[1],
+                end=datetimes[2],
+                room=room102,
+            ),
+            exclude={"datespan", "start", "end", "room"},
         )
 
     @ignore_warnings(category=RemovedInDjango50Warning)
@@ -731,6 +765,21 @@ class ExclusionConstraintTests(PostgreSQLTestCase):
             constraint_name, self.get_constraints(RangesModel._meta.db_table)
         )
 
+    def test_validate_range_adjacent(self):
+        constraint = ExclusionConstraint(
+            name="ints_adjacent",
+            expressions=[("ints", RangeOperators.ADJACENT_TO)],
+            violation_error_message="Custom error message.",
+        )
+        range_obj = RangesModel.objects.create(ints=(20, 50))
+        constraint.validate(RangesModel, range_obj)
+        msg = "Custom error message."
+        with self.assertRaisesMessage(ValidationError, msg):
+            constraint.validate(RangesModel, RangesModel(ints=(10, 20)))
+        constraint.validate(RangesModel, RangesModel(ints=(10, 19)))
+        constraint.validate(RangesModel, RangesModel(ints=(51, 60)))
+        constraint.validate(RangesModel, RangesModel(ints=(10, 20)), exclude={"ints"})
+
     def test_expressions_with_params(self):
         constraint_name = "scene_left_equal"
         self.assertNotIn(constraint_name, self.get_constraints(Scene._meta.db_table))

tests/validation/models.py

@@ -161,3 +161,59 @@ class UniqueFuncConstraintModel(models.Model):
         constraints = [
             models.UniqueConstraint(Lower("field"), name="func_lower_field_uq"),
         ]
+
+
+class Product(models.Model):
+    price = models.IntegerField(null=True)
+    discounted_price = models.IntegerField(null=True)
+
+    class Meta:
+        required_db_features = {
+            "supports_table_check_constraints",
+        }
+        constraints = [
+            models.CheckConstraint(
+                check=models.Q(price__gt=models.F("discounted_price")),
+                name="price_gt_discounted_price_validation",
+            ),
+        ]
+
+
+class ChildProduct(Product):
+    class Meta:
+        required_db_features = {
+            "supports_table_check_constraints",
+        }
+
+
+class UniqueConstraintProduct(models.Model):
+    name = models.CharField(max_length=255)
+    color = models.CharField(max_length=32)
+    rank = models.IntegerField()
+
+    class Meta:
+        constraints = [
+            models.UniqueConstraint(
+                fields=["name", "color"], name="name_color_uniq_validation"
+            ),
+            models.UniqueConstraint(fields=["rank"], name="rank_uniq_validation"),
+        ]
+
+
+class ChildUniqueConstraintProduct(UniqueConstraintProduct):
+    pass
+
+
+class UniqueConstraintConditionProduct(models.Model):
+    name = models.CharField(max_length=255)
+    color = models.CharField(max_length=31, null=True, blank=True)
+
+    class Meta:
+        required_db_features = {"supports_partial_indexes"}
+        constraints = [
+            models.UniqueConstraint(
+                fields=["name"],
+                name="name_without_color_uniq_validation",
+                condition=models.Q(color__isnull=True),
+            ),
+        ]

tests/validation/test_constraints.py

@@ -0,0 +1,95 @@
+from django.core.exceptions import ValidationError
+from django.test import TestCase, skipUnlessDBFeature
+
+from .models import (
+    ChildProduct,
+    ChildUniqueConstraintProduct,
+    Product,
+    UniqueConstraintConditionProduct,
+    UniqueConstraintProduct,
+)
+
+
+class PerformConstraintChecksTest(TestCase):
+    @skipUnlessDBFeature("supports_table_check_constraints")
+    def test_full_clean_with_check_constraints(self):
+        product = Product(price=10, discounted_price=15)
+        with self.assertRaises(ValidationError) as cm:
+            product.full_clean()
+        self.assertEqual(
+            cm.exception.message_dict,
+            {
+                "__all__": [
+                    "Constraint “price_gt_discounted_price_validation” is violated."
+                ]
+            },
+        )
+
+    @skipUnlessDBFeature("supports_table_check_constraints")
+    def test_full_clean_with_check_constraints_on_child_model(self):
+        product = ChildProduct(price=10, discounted_price=15)
+        with self.assertRaises(ValidationError) as cm:
+            product.full_clean()
+        self.assertEqual(
+            cm.exception.message_dict,
+            {
+                "__all__": [
+                    "Constraint “price_gt_discounted_price_validation” is violated."
+                ]
+            },
+        )
+
+    @skipUnlessDBFeature("supports_table_check_constraints")
+    def test_full_clean_with_check_constraints_disabled(self):
+        product = Product(price=10, discounted_price=15)
+        product.full_clean(validate_constraints=False)
+
+    def test_full_clean_with_unique_constraints(self):
+        UniqueConstraintProduct.objects.create(name="product", color="yellow", rank=1)
+        tests = [
+            UniqueConstraintProduct(name="product", color="yellow", rank=1),
+            # Child model.
+            ChildUniqueConstraintProduct(name="product", color="yellow", rank=1),
+        ]
+        for product in tests:
+            with self.subTest(model=product.__class__.__name__):
+                with self.assertRaises(ValidationError) as cm:
+                    product.full_clean()
+                self.assertEqual(
+                    cm.exception.message_dict,
+                    {
+                        "__all__": [
+                            "Unique constraint product with this Name and Color "
+                            "already exists."
+                        ],
+                        "rank": [
+                            "Unique constraint product with this Rank already exists."
+                        ],
+                    },
+                )
+
+    def test_full_clean_with_unique_constraints_disabled(self):
+        UniqueConstraintProduct.objects.create(name="product", color="yellow", rank=1)
+        product = UniqueConstraintProduct(name="product", color="yellow", rank=1)
+        product.full_clean(validate_constraints=False)
+
+    @skipUnlessDBFeature("supports_partial_indexes")
+    def test_full_clean_with_partial_unique_constraints(self):
+        UniqueConstraintConditionProduct.objects.create(name="product")
+        product = UniqueConstraintConditionProduct(name="product")
+        with self.assertRaises(ValidationError) as cm:
+            product.full_clean()
+        self.assertEqual(
+            cm.exception.message_dict,
+            {
+                "__all__": [
+                    "Constraint “name_without_color_uniq_validation” is violated."
+                ]
+            },
+        )
+
+    @skipUnlessDBFeature("supports_partial_indexes")
+    def test_full_clean_with_partial_unique_constraints_disabled(self):
+        UniqueConstraintConditionProduct.objects.create(name="product")
+        product = UniqueConstraintConditionProduct(name="product")
+        product.full_clean(validate_constraints=False)

tests/validation/test_unique.py

@@ -146,10 +146,6 @@ class PerformUniqueChecksTest(TestCase):
             mtv = ModelToValidate(number=10, name="Some Name")
             mtv.full_clean()
 
-    def test_func_unique_check_not_performed(self):
-        with self.assertNumQueries(0):
-            UniqueFuncConstraintModel(field="some name").full_clean()
-
     def test_unique_for_date(self):
         Post.objects.create(
             title="Django 1.0 is released",