Fixed #7210 -- Added F() expressions to query language. See the documentation for details on usage.

Many thanks to:
    * Nicolas Lara, who worked on this feature during the 2008 Google Summer of Code.
    * Alex Gaynor for his help debugging and fixing a number of issues.
    * Malcolm Tredinnick for his invaluable review notes.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9792 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/__init__.py

@@ -3,6 +3,7 @@ from django.core.exceptions import ObjectDoesNotExist, ImproperlyConfigured
 from django.db import connection
 from django.db.models.loading import get_apps, get_app, get_models, get_model, register_models
 from django.db.models.query import Q
+from django.db.models.expressions import F
 from django.db.models.manager import Manager
 from django.db.models.base import Model
 from django.db.models.aggregates import *

django/db/models/expressions.py

@@ -0,0 +1,110 @@
+from copy import deepcopy
+from datetime import datetime
+
+from django.utils import tree
+
+class ExpressionNode(tree.Node):
+    """
+    Base class for all query expressions.
+    """
+    # Arithmetic connectors
+    ADD = '+'
+    SUB = '-'
+    MUL = '*'
+    DIV = '/'
+    MOD = '%%'  # This is a quoted % operator - it is quoted
+                # because it can be used in strings that also
+                # have parameter substitution.
+
+    # Bitwise operators
+    AND = '&'
+    OR = '|'
+
+    def __init__(self, children=None, connector=None, negated=False):
+        if children is not None and len(children) > 1 and connector is None:
+            raise TypeError('You have to specify a connector.')
+        super(ExpressionNode, self).__init__(children, connector, negated)
+
+    def _combine(self, other, connector, reversed, node=None):
+        if reversed:
+            obj = ExpressionNode([other], connector)
+            obj.add(node or self, connector)
+        else:
+            obj = node or ExpressionNode([self], connector)
+            obj.add(other, connector)
+        return obj
+
+    ###################
+    # VISITOR METHODS #
+    ###################
+
+    def prepare(self, evaluator, query, allow_joins):
+        return evaluator.prepare_node(self, query, allow_joins)
+
+    def evaluate(self, evaluator, qn):
+        return evaluator.evaluate_node(self, qn)
+
+    #############
+    # OPERATORS #
+    #############
+
+    def __add__(self, other):
+        return self._combine(other, self.ADD, False)
+
+    def __sub__(self, other):
+        return self._combine(other, self.SUB, False)
+
+    def __mul__(self, other):
+        return self._combine(other, self.MUL, False)
+
+    def __div__(self, other):
+        return self._combine(other, self.DIV, False)
+
+    def __mod__(self, other):
+        return self._combine(other, self.MOD, False)
+
+    def __and__(self, other):
+        return self._combine(other, self.AND, False)
+
+    def __or__(self, other):
+        return self._combine(other, self.OR, False)
+
+    def __radd__(self, other):
+        return self._combine(other, self.ADD, True)
+
+    def __rsub__(self, other):
+        return self._combine(other, self.SUB, True)
+
+    def __rmul__(self, other):
+        return self._combine(other, self.MUL, True)
+
+    def __rdiv__(self, other):
+        return self._combine(other, self.DIV, True)
+
+    def __rmod__(self, other):
+        return self._combine(other, self.MOD, True)
+
+    def __rand__(self, other):
+        return self._combine(other, self.AND, True)
+
+    def __ror__(self, other):
+        return self._combine(other, self.OR, True)
+
+class F(ExpressionNode):
+    """
+    An expression representing the value of the given field.
+    """
+    def __init__(self, name):
+        super(F, self).__init__(None, None, False)
+        self.name = name
+
+    def __deepcopy__(self, memodict):
+        obj = super(F, self).__deepcopy__(memodict)
+        obj.name = self.name
+        return obj
+
+    def prepare(self, evaluator, query, allow_joins):
+        return evaluator.prepare_leaf(self, query, allow_joins)
+
+    def evaluate(self, evaluator, qn):
+        return evaluator.evaluate_leaf(self, qn)

django/db/models/fields/__init__.py

@@ -194,8 +194,13 @@ class Field(object):
     def get_db_prep_lookup(self, lookup_type, value):
         "Returns field's value prepared for database lookup."
         if hasattr(value, 'as_sql'):
+            # If the value has a relabel_aliases method, it will need to
+            # be invoked before the final SQL is evaluated
+            if hasattr(value, 'relabel_aliases'):
+                return value
             sql, params = value.as_sql()
             return QueryWrapper(('(%s)' % sql), params)
+
         if lookup_type in ('regex', 'iregex', 'month', 'day', 'search'):
             return [value]
         elif lookup_type in ('exact', 'gt', 'gte', 'lt', 'lte'):
@@ -309,7 +314,7 @@ class Field(object):
             if callable(self.default):
                 defaults['show_hidden_initial'] = True
         if self.choices:
-            # Fields with choices get special treatment. 
+            # Fields with choices get special treatment.
             include_blank = self.blank or not (self.has_default() or 'initial' in kwargs)
             defaults['choices'] = self.get_choices(include_blank=include_blank)
             defaults['coerce'] = self.to_python

django/db/models/fields/related.py

@@ -141,6 +141,10 @@ class RelatedField(object):
             return v
 
         if hasattr(value, 'as_sql'):
+            # If the value has a relabel_aliases method, it will need to
+            # be invoked before the final SQL is evaluated
+            if hasattr(value, 'relabel_aliases'):
+                return value
             sql, params = value.as_sql()
             return QueryWrapper(('(%s)' % sql), params)
 

django/db/models/query_utils.py

@@ -17,6 +17,9 @@ class QueryWrapper(object):
     def __init__(self, sql, params):
         self.data = sql, params
 
+    def as_sql(self, qn=None):
+        return self.data
+
 class Q(tree.Node):
     """
     Encapsulates filters as objects that can then be combined logically (using

django/db/models/sql/expressions.py

@@ -0,0 +1,92 @@
+from django.core.exceptions import FieldError
+from django.db import connection
+from django.db.models.fields import FieldDoesNotExist
+from django.db.models.sql.constants import LOOKUP_SEP
+
+class SQLEvaluator(object):
+    def __init__(self, expression, query, allow_joins=True):
+        self.expression = expression
+        self.opts = query.get_meta()
+        self.cols = {}
+
+        self.contains_aggregate = False
+        self.expression.prepare(self, query, allow_joins)
+
+    def as_sql(self, qn=None):
+        return self.expression.evaluate(self, qn)
+
+    def relabel_aliases(self, change_map):
+        for node, col in self.cols.items():
+            self.cols[node] = (change_map.get(col[0], col[0]), col[1])
+
+    #####################################################
+    # Vistor methods for initial expression preparation #
+    #####################################################
+
+    def prepare_node(self, node, query, allow_joins):
+        for child in node.children:
+            if hasattr(child, 'prepare'):
+                child.prepare(self, query, allow_joins)
+
+    def prepare_leaf(self, node, query, allow_joins):
+        if not allow_joins and LOOKUP_SEP in node.name:
+            raise FieldError("Joined field references are not permitted in this query")
+
+        field_list = node.name.split(LOOKUP_SEP)
+        if (len(field_list) == 1 and
+            node.name in query.aggregate_select.keys()):
+            self.contains_aggregate = True
+            self.cols[node] = query.aggregate_select[node.name]
+        else:
+            try:
+                field, source, opts, join_list, last, _ = query.setup_joins(
+                    field_list, query.get_meta(),
+                    query.get_initial_alias(), False)
+                _, _, col, _, join_list = query.trim_joins(source, join_list, last, False)
+
+                self.cols[node] = (join_list[-1], col)
+            except FieldDoesNotExist:
+                raise FieldError("Cannot resolve keyword %r into field. "
+                                 "Choices are: %s" % (self.name,
+                                                      [f.name for f in self.opts.fields]))
+
+    ##################################################
+    # Vistor methods for final expression evaluation #
+    ##################################################
+
+    def evaluate_node(self, node, qn):
+        if not qn:
+            qn = connection.ops.quote_name
+
+        expressions = []
+        expression_params = []
+        for child in node.children:
+            if hasattr(child, 'evaluate'):
+                sql, params = child.evaluate(self, qn)
+            else:
+                try:
+                    sql, params = qn(child), ()
+                except:
+                    sql, params = str(child), ()
+
+            if hasattr(child, 'children') > 1:
+                format = '(%s)'
+            else:
+                format = '%s'
+
+            if sql:
+                expressions.append(format % sql)
+                expression_params.extend(params)
+        conn = ' %s ' % node.connector
+
+        return conn.join(expressions), expression_params
+
+    def evaluate_leaf(self, node, qn):
+        if not qn:
+            qn = connection.ops.quote_name
+
+        col = self.cols[node]
+        if hasattr(col, 'as_sql'):
+            return col.as_sql(qn), ()
+        else:
+            return '%s.%s' % (qn(col[0]), qn(col[1])), ()

django/db/models/sql/query.py

@@ -18,6 +18,7 @@ from django.db.models import signals
 from django.db.models.fields import FieldDoesNotExist
 from django.db.models.query_utils import select_related_descend
 from django.db.models.sql import aggregates as base_aggregates_module
+from django.db.models.sql.expressions import SQLEvaluator
 from django.db.models.sql.where import WhereNode, Constraint, EverythingNode, AND, OR
 from django.core.exceptions import FieldError
 from datastructures import EmptyResultSet, Empty, MultiJoin
@@ -1271,6 +1272,10 @@ class BaseQuery(object):
         else:
             lookup_type = parts.pop()
 
+        # By default, this is a WHERE clause. If an aggregate is referenced
+        # in the value, the filter will be promoted to a HAVING
+        having_clause = False
+
         # Interpret '__exact=None' as the sql 'is NULL'; otherwise, reject all
         # uses of None as a query value.
         if value is None:
@@ -1284,6 +1289,10 @@ class BaseQuery(object):
             value = True
         elif callable(value):
             value = value()
+        elif hasattr(value, 'evaluate'):
+            # If value is a query expression, evaluate it
+            value = SQLEvaluator(value, self)
+            having_clause = value.contains_aggregate
 
         for alias, aggregate in self.aggregate_select.items():
             if alias == parts[0]:
@@ -1340,8 +1349,13 @@ class BaseQuery(object):
             self.promote_alias_chain(join_it, join_promote)
             self.promote_alias_chain(table_it, table_promote)
 
-        self.where.add((Constraint(alias, col, field), lookup_type, value),
+
-            connector)
+        if having_clause:
+            self.having.add((Constraint(alias, col, field), lookup_type, value),
+                connector)
+        else:
+            self.where.add((Constraint(alias, col, field), lookup_type, value),
+                connector)
 
         if negate:
             self.promote_alias_chain(join_list)

django/db/models/sql/subqueries.py

@@ -5,6 +5,7 @@ Query subclasses which provide extra functionality beyond simple data retrieval.
 from django.core.exceptions import FieldError
 from django.db.models.sql.constants import *
 from django.db.models.sql.datastructures import Date
+from django.db.models.sql.expressions import SQLEvaluator
 from django.db.models.sql.query import Query
 from django.db.models.sql.where import AND, Constraint
 
@@ -136,7 +137,11 @@ class UpdateQuery(Query):
         result.append('SET')
         values, update_params = [], []
         for name, val, placeholder in self.values:
-            if val is not None:
+            if hasattr(val, 'as_sql'):
+                sql, params = val.as_sql(qn)
+                values.append('%s = %s' % (qn(name), sql))
+                update_params.extend(params)
+            elif val is not None:
                 values.append('%s = %s' % (qn(name), placeholder))
                 update_params.append(val)
             else:
@@ -251,6 +256,8 @@ class UpdateQuery(Query):
             else:
                 placeholder = '%s'
 
+            if hasattr(val, 'evaluate'):
+                val = SQLEvaluator(val, self, allow_joins=False)
             if model:
                 self.add_related_update(model, field.column, val, placeholder)
             else:

django/db/models/sql/where.py

@@ -97,6 +97,7 @@ class WhereNode(tree.Node):
                 else:
                     # A leaf node in the tree.
                     sql, params = self.make_atom(child, qn)
+
             except EmptyResultSet:
                 if self.connector == AND and not self.negated:
                     # We can bail out early in this particular case (only).
@@ -114,6 +115,7 @@ class WhereNode(tree.Node):
                 if self.negated:
                     empty = True
                 continue
+
             empty = False
             if sql:
                 result.append(sql)
@@ -151,8 +153,9 @@ class WhereNode(tree.Node):
         else:
             cast_sql = '%s'
 
-        if isinstance(params, QueryWrapper):
+        if hasattr(params, 'as_sql'):
-            extra, params = params.data
+            extra, params = params.as_sql(qn)
+            cast_sql = ''
         else:
             extra = ''
 
@@ -214,6 +217,9 @@ class WhereNode(tree.Node):
                 if elt[0] in change_map:
                     elt[0] = change_map[elt[0]]
                     node.children[pos] = (tuple(elt),) + child[1:]
+                # Check if the query value also requires relabelling
+                if hasattr(child[3], 'relabel_aliases'):
+                    child[3].relabel_aliases(change_map)
 
 class EverythingNode(object):
     """

docs/ref/databases.txt

@@ -163,7 +163,7 @@ table (usually called ``django_session`` and the table
 Connecting to the database
 --------------------------
 
-Refer to the :ref:`settings documentation <ref-settings>`. 
+Refer to the :ref:`settings documentation <ref-settings>`.
 
 Connection settings are used in this order:
 
@@ -262,9 +262,9 @@ of whether ``unique=True`` is specified or not.
 
 .. _sqlite-notes:
 
-SQLite notes 
+SQLite notes
-============ 
+============
- 
+
 SQLite_ provides an excellent development alternative for applications that
 are predominantly read-only or require a smaller installation footprint. As
 with all database servers, though, there are some differences that are
@@ -294,21 +294,21 @@ the ``extra()`` QuerySet method. The bug can be identified by the error message
 ``OperationalError: ORDER BY terms must not be non-integer constants``. The
 problem can be solved updating SQLite to version 3.3.6 or newer, possibly also
 updating the ``pysqlite2`` Python module in the process.
- 
+
-.. _contain a bug: http://www.sqlite.org/cvstrac/tktview?tn=1768 
+.. _contain a bug: http://www.sqlite.org/cvstrac/tktview?tn=1768
- 
+
-This has a very low impact because 3.3.6 was released in April 2006, so most 
+This has a very low impact because 3.3.6 was released in April 2006, so most
-current binary distributions for different platforms include newer version of 
+current binary distributions for different platforms include newer version of
-SQLite usable from Python through either the ``pysqlite2`` or the ``sqlite3`` 
+SQLite usable from Python through either the ``pysqlite2`` or the ``sqlite3``
-modules. 
+modules.
- 
+
-However, in the case of Windows, the official binary distribution of the stable 
+However, in the case of Windows, the official binary distribution of the stable
-release of Python 2.5 (2.5.2, as of this writing) includes SQLite 3.3.4, so the bug can 
+release of Python 2.5 (2.5.2, as of this writing) includes SQLite 3.3.4, so the bug can
-make itself evident in that platform. There are (as of Django 1.0) even three 
+make itself evident in that platform. There are (as of Django 1.0) even three
-tests in the Django test suite that will fail when run under this setup.  As 
+tests in the Django test suite that will fail when run under this setup.  As
-described above, this can be solved by downloading and installing a newer 
+described above, this can be solved by downloading and installing a newer
-version of ``pysqlite2`` (``pysqlite-2.x.x.win32-py2.5.exe``) that includes and 
+version of ``pysqlite2`` (``pysqlite-2.x.x.win32-py2.5.exe``) that includes and
-uses a newer version of SQLite. Python 2.6 ships with a newer version of 
+uses a newer version of SQLite. Python 2.6 ships with a newer version of
 SQLite and is not affected by this issue.
 
 If you are in such platform and find yourself in the need to update
@@ -317,6 +317,23 @@ If you are in such platform and find yourself in the need to update
 attempts to import ``pysqlite2`` before than ``sqlite3`` and so it can take
 advantage of the new ``pysqlite2``/SQLite versions.
 
+Version 3.5.9
+-------------
+
+The Ubuntu "Intrepid Ibex" SQLite 3.5.9-3 package contains a bug that causes
+problems with the evaluation of query expressions. If you are using Ubuntu
+"Intrepid Ibex", you will need to find an alternate source for SQLite
+packages, or install SQLite from source.
+
+At one time, Debian Lenny shipped with the same malfunctioning SQLite 3.5.9-3
+package. However the Debian project has subsequently issued updated versions
+of the SQLite package that correct these bugs. If you find you are getting
+unexpected results under Debian, ensure you have updated your SQLite package
+to 3.5.9-5 or later.
+
+The problem does not appear to exist with other versions of SQLite packaged
+with other operating systems.
+
 Version 3.6.2
 --------------
 
@@ -348,14 +365,14 @@ database user must have privileges to run the following commands:
     * CREATE SEQUENCE
     * CREATE PROCEDURE
     * CREATE TRIGGER
-    
+
 To run Django's test suite, the user needs these *additional* privileges:
 
     * CREATE USER
     * DROP USER
     * CREATE TABLESPACE
     * DROP TABLESPACE
-    
+
 Connecting to the database
 --------------------------
 

docs/topics/db/queries.txt

@@ -8,8 +8,8 @@ Making queries
 
 Once you've created your :ref:`data models <topics-db-models>`, Django
 automatically gives you a database-abstraction API that lets you create,
-retrieve, update and delete objects. This document explains how to use this 
+retrieve, update and delete objects. This document explains how to use this
-API. Refer to the :ref:`data model reference <ref-models-index>` for full 
+API. Refer to the :ref:`data model reference <ref-models-index>` for full
 details of all the various model lookup options.
 
 Throughout this guide (and in the reference), we'll refer to the following
@@ -39,6 +39,9 @@ models, which comprise a weblog application:
         body_text = models.TextField()
         pub_date = models.DateTimeField()
         authors = models.ManyToManyField(Author)
+        n_comments = models.IntegerField()
+        n_pingbacks = models.IntegerField()
+        rating = models.IntegerField()
 
         def __unicode__(self):
             return self.headline
@@ -94,11 +97,11 @@ Saving ``ForeignKey`` and ``ManyToManyField`` fields
 ----------------------------------------------------
 
 Updating ``ForeignKey`` fields works exactly the same way as saving a normal
-field; simply assign an object of the right type to the field in question:: 
+field; simply assign an object of the right type to the field in question::
 
-    >>> cheese_blog = Blog.objects.get(name="Cheddar Talk") 
+    >>> cheese_blog = Blog.objects.get(name="Cheddar Talk")
-    >>> entry.blog = cheese_blog 
+    >>> entry.blog = cheese_blog
-    >>> entry.save() 
+    >>> entry.save()
 
 Updating a ``ManyToManyField`` works a little differently; use the ``add()``
 method on the field to add a record to the relation::
@@ -245,7 +248,7 @@ this example::
     >>> q = q.filter(pub_date__lte=datetime.now())
     >>> q = q.exclude(body_text__icontains="food")
     >>> print q
-    
+
 Though this looks like three database hits, in fact it hits the database only
 once, at the last line (``print q``). In general, the results of a ``QuerySet``
 aren't fetched from the database until you "ask" for them. When you do, the
@@ -333,15 +336,15 @@ you'll probably use:
 
     :lookup:`exact`
         An "exact" match. For example::
-        
+
             >>> Entry.objects.get(headline__exact="Man bites dog")
 
         Would generate SQL along these lines:
-        
+
         .. code-block:: sql
 
             SELECT ... WHERE headline = 'Man bites dog';
-            
+
         If you don't provide a lookup type -- that is, if your keyword argument
         doesn't contain a double underscore -- the lookup type is assumed to be
         ``exact``.
@@ -352,36 +355,36 @@ you'll probably use:
             >>> Blog.objects.get(id=14)         # __exact is implied
 
         This is for convenience, because ``exact`` lookups are the common case.
-        
+
     :lookup:`iexact`
         A case-insensitive match. So, the query::
-        
+
             >>> Blog.objects.get(name__iexact="beatles blog")
-            
+
         Would match a ``Blog`` titled "Beatles Blog", "beatles blog", or even
         "BeAtlES blOG".
-    
+
     :lookup:`contains`
         Case-sensitive containment test. For example::
 
             Entry.objects.get(headline__contains='Lennon')
 
         Roughly translates to this SQL:
-        
+
         .. code-block:: sql
 
             SELECT ... WHERE headline LIKE '%Lennon%';
 
         Note this will match the headline ``'Today Lennon honored'`` but not
         ``'today lennon honored'``.
-        
+
         There's also a case-insensitive version, :lookup:`icontains`.
-        
+
     :lookup:`startswith`, :lookup:`endswith`
         Starts-with and ends-with search, respectively. There are also
         case-insensitive versions called :lookup:`istartswith` and
         :lookup:`iendswith`.
-    
+
 Again, this only scratches the surface. A complete reference can be found in the
 :ref:`field lookup reference <field-lookups>`.
 
@@ -485,6 +488,48 @@ are talking about the same multi-valued relation). Conditions in subsequent
 ``filter()`` or ``exclude()`` calls that refer to the same relation may end up
 filtering on different linked objects.
 
+.. _query-expressions:
+
+Filters can reference fields on the model
+-----------------------------------------
+
+.. versionadded:: 1.1
+
+In the examples given so far, we have constructed filters that compare
+the value of a model field with a constant. But what if you want to compare
+the value of a model field with another field on the same model?
+
+Django provides the ``F()`` object to allow such comparisons. Instances
+of ``F()`` act as a reference to a model field within a query. These
+references can then be used in query filters to compare the values of two
+different fields on the same model instance.
+
+For example, to find a list of all blog entries that have had more comments
+than pingbacks, we construct an ``F()`` object to reference the comment count,
+and use that ``F()`` object in the query::
+
+    >>> Entry.objects.filter(n_pingbacks__lt=F('n_comments'))
+
+Django supports the use of addition, subtraction, multiplication,
+division and modulo arithmetic with ``F()`` objects, both with constants
+and with other ``F()`` objects. To find all the blog entries with *twice* as
+many comments as pingbacks, we modify the query::
+
+    >>> Entry.objects.filter(n_pingbacks__lt=F('n_comments') * 2)
+
+To find all the entries where the sum of the pingback count and comment count
+is greater than the rating of the entry, we would issue the query::
+
+    >>> Entry.objects.filter(rating__lt=F('n_comments') + F('n_pingbacks'))
+
+You can also use the double underscore notation to span relationships in
+an ``F()`` object. An ``F()`` object with a double underscore will introduce
+any joins needed to access the related object. For example, to retrieve all
+the entries where the author's name is the same as the blog name, we could
+issue the query:
+
+    >>> Entry.objects.filter(author__name=F('blog__name'))
+
 The pk lookup shortcut
 ----------------------
 
@@ -503,7 +548,7 @@ can be combined with ``pk`` to perform a query on the primary key of a model::
 
     # Get blogs entries with id 1, 4 and 7
     >>> Blog.objects.filter(pk__in=[1,4,7])
-    
+
     # Get all blog entries with id > 14
     >>> Blog.objects.filter(pk__gt=14)
 
@@ -728,7 +773,7 @@ To update ``ForeignKey`` fields, set the new value to be the new model
 instance you want to point to. Example::
 
     >>> b = Blog.objects.get(pk=1)
-    
+
     # Change every Entry so that it belongs to this Blog.
     >>> Entry.objects.all().update(blog=b)
 
@@ -749,6 +794,21 @@ Just loop over them and call ``save()``::
     for item in my_queryset:
         item.save()
 
+Calls to update can also use :ref:`F() objects <query-expressions>` to update
+one field based on the value of another field in the model. This is especially
+useful for incrementing counters based upon their current value. For example, to
+increment the pingback count for every entry in the blog::
+
+    >>> Entry.objects.all().update(n_pingbacks=F('n_pingbacks') + 1)
+
+However, unlike ``F()`` objects in filter and exclude clauses, you can't
+introduce joins when you use ``F()`` objects in an update -- you can only
+reference fields local to the model being updated. If you attempt to introduce
+a join with an ``F()`` object, a ``FieldError`` will be raised::
+
+    # THIS WILL RAISE A FieldError
+    >>> Entry.objects.update(headline=F('blog__name'))
+
 Related objects
 ===============
 

tests/modeltests/expressions/models.py

@@ -0,0 +1,71 @@
+"""
+Tests for F() query expression syntax.
+"""
+
+from django.db import models
+
+class Employee(models.Model):
+    firstname = models.CharField(max_length=50)
+    lastname = models.CharField(max_length=50)
+
+    def __unicode__(self):
+        return u'%s %s' % (self.firstname, self.lastname)
+
+class Company(models.Model):
+    name = models.CharField(max_length=100)
+    num_employees = models.PositiveIntegerField()
+    num_chairs = models.PositiveIntegerField()
+    ceo = models.ForeignKey(
+        Employee,
+        related_name='company_ceo_set')
+    point_of_contact = models.ForeignKey(
+        Employee,
+        related_name='company_point_of_contact_set',
+        null=True)
+
+    def __unicode__(self):
+        return self.name
+
+
+__test__ = {'API_TESTS': """
+>>> from django.db.models import F
+
+>>> Company(name='Example Inc.', num_employees=2300, num_chairs=5,
+...     ceo=Employee.objects.create(firstname='Joe', lastname='Smith')).save()
+>>> Company(name='Foobar Ltd.', num_employees=3, num_chairs=3,
+...     ceo=Employee.objects.create(firstname='Frank', lastname='Meyer')).save()
+>>> Company(name='Test GmbH', num_employees=32, num_chairs=1,
+...     ceo=Employee.objects.create(firstname='Max', lastname='Mustermann')).save()
+
+# We can filter for companies where the number of employees is greater than the
+# number of chairs.
+
+>>> Company.objects.filter(num_employees__gt=F('num_chairs'))
+[<Company: Example Inc.>, <Company: Test GmbH>]
+
+# The relation of a foreign key can become copied over to an other foreign key.
+
+>>> Company.objects.update(point_of_contact=F('ceo'))
+3
+
+>>> [c.point_of_contact for c in Company.objects.all()]
+[<Employee: Joe Smith>, <Employee: Frank Meyer>, <Employee: Max Mustermann>]
+
+>>> c = Company.objects.all()[0]
+>>> c.point_of_contact = Employee.objects.create(firstname="Guido", lastname="van Rossum")
+>>> c.save()
+
+# F Expressions can also span joins
+>>> Company.objects.filter(ceo__firstname=F('point_of_contact__firstname')).distinct()
+[<Company: Foobar Ltd.>, <Company: Test GmbH>]
+
+>>> _ = Company.objects.exclude(ceo__firstname=F('point_of_contact__firstname')).update(name='foo')
+>>> Company.objects.exclude(ceo__firstname=F('point_of_contact__firstname')).get().name
+u'foo'
+
+>>> _ = Company.objects.exclude(ceo__firstname=F('point_of_contact__firstname')).update(name=F('point_of_contact__lastname'))
+Traceback (most recent call last):
+...
+FieldError: Joined field references are not permitted in this query
+
+"""}

tests/regressiontests/aggregation_regress/models.py

@@ -50,7 +50,7 @@ class Store(models.Model):
 #Extra does not play well with values. Modify the tests if/when this is fixed.
 __test__ = {'API_TESTS': """
 >>> from django.core import management
->>> from django.db.models import get_app
+>>> from django.db.models import get_app, F
 
 # Reset the database representation of this app.
 # This will return the database to a clean initial state.
@@ -164,6 +164,21 @@ FieldError: Cannot resolve keyword 'foo' into field. Choices are: authors, id, i
 >>> len(Book.objects.annotate(num_authors=Count('authors')).exclude(num_authors__lt=2).filter(num_authors__lt=3))
 2
 
+# Aggregates can be used with F() expressions
+# ... where the F() is pushed into the HAVING clause
+>>> Publisher.objects.annotate(num_books=Count('book')).filter(num_books__lt=F('num_awards')/2).values('name','num_books','num_awards')
+[{'num_books': 2, 'name': u'Prentice Hall', 'num_awards': 7}, {'num_books': 1, 'name': u'Morgan Kaufmann', 'num_awards': 9}]
+
+>>> Publisher.objects.annotate(num_books=Count('book')).exclude(num_books__lt=F('num_awards')/2).values('name','num_books','num_awards')
+[{'num_books': 2, 'name': u'Apress', 'num_awards': 3}, {'num_books': 1, 'name': u'Sams', 'num_awards': 1}, {'num_books': 0, 'name': u"Jonno's House of Books", 'num_awards': 0}]
+
+# ... and where the F() references an aggregate
+>>> Publisher.objects.annotate(num_books=Count('book')).filter(num_awards__gt=2*F('num_books')).values('name','num_books','num_awards')
+[{'num_books': 2, 'name': u'Prentice Hall', 'num_awards': 7}, {'num_books': 1, 'name': u'Morgan Kaufmann', 'num_awards': 9}]
+
+>>> Publisher.objects.annotate(num_books=Count('book')).exclude(num_books__lt=F('num_awards')/2).values('name','num_books','num_awards')
+[{'num_books': 2, 'name': u'Apress', 'num_awards': 3}, {'num_books': 1, 'name': u'Sams', 'num_awards': 1}, {'num_books': 0, 'name': u"Jonno's House of Books", 'num_awards': 0}]
+
 # Regression for #10089: Check handling of empty result sets with aggregates
 >>> Book.objects.filter(id__in=[]).count()
 0

tests/regressiontests/expressions_regress/models.py

@@ -0,0 +1,133 @@
+"""
+Spanning tests for all the operations that F() expressions can perform.
+"""
+
+from django.db import models
+
+#
+# Model for testing arithmetic expressions.
+#
+
+class Number(models.Model):
+    integer = models.IntegerField()
+    float = models.FloatField(null=True)
+
+    def __unicode__(self):
+        return u'%i, %.3f' % (self.integer, self.float)
+
+
+__test__ = {'API_TESTS': """
+>>> from django.db.models import F
+
+>>> Number(integer=-1).save()
+>>> Number(integer=42).save()
+>>> Number(integer=1337).save()
+
+We can fill a value in all objects with an other value of the same object.
+
+>>> Number.objects.update(float=F('integer'))
+3
+>>> Number.objects.all()
+[<Number: -1, -1.000>, <Number: 42, 42.000>, <Number: 1337, 1337.000>]
+
+We can increment a value of all objects in a query set.
+
+>>> Number.objects.filter(integer__gt=0).update(integer=F('integer') + 1)
+2
+>>> Number.objects.all()
+[<Number: -1, -1.000>, <Number: 43, 42.000>, <Number: 1338, 1337.000>]
+
+We can filter for objects, where a value is not equals the value of an other field.
+
+>>> Number.objects.exclude(float=F('integer'))
+[<Number: 43, 42.000>, <Number: 1338, 1337.000>]
+
+Complex expressions of different connection types are possible.
+
+>>> n = Number.objects.create(integer=10, float=123.45)
+
+>>> Number.objects.filter(pk=n.pk).update(float=F('integer') + F('float') * 2)
+1
+>>> Number.objects.get(pk=n.pk)
+<Number: 10, 256.900>
+
+# All supported operators work as expected.
+
+>>> n = Number.objects.create(integer=42, float=15.5)
+
+# Left hand operators
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=F('integer') + 15, float=F('float') + 42.7)
+>>> Number.objects.get(pk=n.pk) # LH Addition of floats and integers
+<Number: 57, 58.200>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=F('integer') - 15, float=F('float') - 42.7)
+>>> Number.objects.get(pk=n.pk) # LH Subtraction of floats and integers
+<Number: 27, -27.200>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=F('integer') * 15, float=F('float') * 42.7)
+>>> Number.objects.get(pk=n.pk) # Multiplication of floats and integers
+<Number: 630, 661.850>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=F('integer') / 2, float=F('float') / 42.7)
+>>> Number.objects.get(pk=n.pk) # LH Division of floats and integers
+<Number: 21, 0.363>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=F('integer') % 20)
+>>> Number.objects.get(pk=n.pk) # LH Modulo arithmetic on integers
+<Number: 2, 15.500>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=F('integer') & 56)
+>>> Number.objects.get(pk=n.pk) # LH Bitwise ands on integers
+<Number: 40, 15.500>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=F('integer') | 48)
+>>> Number.objects.get(pk=n.pk) # LH Bitwise or on integers
+<Number: 58, 15.500>
+
+# Right hand operators
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=15 + F('integer'), float=42.7 + F('float'))
+>>> Number.objects.get(pk=n.pk) # RH Addition of floats and integers
+<Number: 57, 58.200>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=15 - F('integer'), float=42.7 - F('float'))
+>>> Number.objects.get(pk=n.pk) # RH Subtraction of floats and integers
+<Number: -27, 27.200>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=15 * F('integer'), float=42.7 * F('float'))
+>>> Number.objects.get(pk=n.pk) # RH Multiplication of floats and integers
+<Number: 630, 661.850>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=640 / F('integer'), float=42.7 / F('float'))
+>>> Number.objects.get(pk=n.pk) # RH Division of floats and integers
+<Number: 15, 2.755>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=69 % F('integer'))
+>>> Number.objects.get(pk=n.pk) # RH Modulo arithmetic on integers
+<Number: 27, 15.500>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=15 & F('integer'))
+>>> Number.objects.get(pk=n.pk) # RH Bitwise ands on integers
+<Number: 10, 15.500>
+
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=42, float=15.5)
+>>> _ = Number.objects.filter(pk=n.pk).update(integer=15 | F('integer'))
+>>> Number.objects.get(pk=n.pk) # RH Bitwise or on integers
+<Number: 47, 15.500>
+
+
+"""}