Fixed #30033 -- Conformed to the recommended table alterations procedure on SQlite3.
Refs #29182.
The previous implementation was following a procedure explicitly documented
as incorrect and was the origin of the breakage experienced on SQLite 3.26
release that were addressed by c8ffdbe514
.
Thanks to Richard Hipp for pointing out the usage of the incorrect procedure.
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@ -1,4 +1,3 @@
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import contextlib
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import copy
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from decimal import Decimal
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@ -33,6 +32,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
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def __exit__(self, exc_type, exc_value, traceback):
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super().__exit__(exc_type, exc_value, traceback)
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self.connection.check_constraints()
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self.connection.cursor().execute('PRAGMA legacy_alter_table = OFF')
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self.connection.enable_constraint_checking()
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@ -139,11 +139,17 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
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"""
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Shortcut to transform a model from old_model into new_model
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This follows the correct procedure to perform non-rename or column
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addition operations based on SQLite's documentation
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https://www.sqlite.org/lang_altertable.html#caution
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The essential steps are:
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1. rename the model's existing table, e.g. "app_model" to "app_model__old"
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2. create a table with the updated definition called "app_model"
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3. copy the data from the old renamed table to the new table
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4. delete the "app_model__old" table
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1. Create a table with the updated definition called "new__app_model"
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2. Copy the data from the existing "app_model" table to the new table
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3. Drop the "app_model" table
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4. Rename the "new__app_model" table to "app_model"
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5. Restore any index of the previous "app_model" table.
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"""
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# Self-referential fields must be recreated rather than copied from
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# the old model to ensure their remote_field.field_name doesn't refer
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@ -205,11 +211,6 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
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# Work inside a new app registry
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apps = Apps()
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# Provide isolated instances of the fields to the new model body so
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# that the existing model's internals aren't interfered with when
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# the dummy model is constructed.
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body = copy.deepcopy(body)
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# Work out the new value of unique_together, taking renames into
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# account
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unique_together = [
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@ -233,7 +234,16 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
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constraints = list(model._meta.constraints)
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# Construct a new model for the new state
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# Provide isolated instances of the fields to the new model body so
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# that the existing model's internals aren't interfered with when
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# the dummy model is constructed.
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body_copy = copy.deepcopy(body)
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# Construct a new model with the new fields to allow self referential
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# primary key to resolve to. This model won't ever be materialized as a
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# table and solely exists for foreign key reference resolution purposes.
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# This wouldn't be required if the schema editor was operating on model
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# states instead of rendered models.
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meta_contents = {
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'app_label': model._meta.app_label,
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'db_table': model._meta.db_table,
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@ -244,41 +254,45 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
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'apps': apps,
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}
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meta = type("Meta", (), meta_contents)
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body['Meta'] = meta
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body['__module__'] = model.__module__
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body_copy['Meta'] = meta
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body_copy['__module__'] = model.__module__
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type(model._meta.object_name, model.__bases__, body_copy)
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temp_model = type(model._meta.object_name, model.__bases__, body)
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# Construct a model with a renamed table name.
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body_copy = copy.deepcopy(body)
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meta_contents = {
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'app_label': model._meta.app_label,
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'db_table': 'new__%s' % model._meta.db_table,
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'unique_together': unique_together,
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'index_together': index_together,
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'indexes': indexes,
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'constraints': constraints,
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'apps': apps,
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}
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meta = type("Meta", (), meta_contents)
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body_copy['Meta'] = meta
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body_copy['__module__'] = model.__module__
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new_model = type('New%s' % model._meta.object_name, model.__bases__, body_copy)
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# We need to modify model._meta.db_table, but everything explodes
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# if the change isn't reversed before the end of this method. This
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# context manager helps us avoid that situation.
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@contextlib.contextmanager
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def altered_table_name(model, temporary_table_name):
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original_table_name = model._meta.db_table
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model._meta.db_table = temporary_table_name
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yield
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model._meta.db_table = original_table_name
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# Create a new table with the updated schema.
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self.create_model(new_model)
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with altered_table_name(model, model._meta.db_table + "__old"):
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# Rename the old table to make way for the new
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self.alter_db_table(
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model, temp_model._meta.db_table, model._meta.db_table,
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disable_constraints=False,
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)
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# Create a new table with the updated schema.
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self.create_model(temp_model)
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# Copy data from the old table into the new table
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self.execute("INSERT INTO %s (%s) SELECT %s FROM %s" % (
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self.quote_name(new_model._meta.db_table),
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', '.join(self.quote_name(x) for x in mapping),
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', '.join(mapping.values()),
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self.quote_name(model._meta.db_table),
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))
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# Copy data from the old table into the new table
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field_maps = list(mapping.items())
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self.execute("INSERT INTO %s (%s) SELECT %s FROM %s" % (
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self.quote_name(temp_model._meta.db_table),
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', '.join(self.quote_name(x) for x, y in field_maps),
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', '.join(y for x, y in field_maps),
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self.quote_name(model._meta.db_table),
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))
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# Delete the old table to make way for the new
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self.delete_model(model, handle_autom2m=False)
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# Delete the old table
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self.delete_model(model, handle_autom2m=False)
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# Rename the new table to take way for the old
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self.alter_db_table(
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new_model, new_model._meta.db_table, model._meta.db_table,
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disable_constraints=False,
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)
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# Run deferred SQL on correct table
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for sql in self.deferred_sql:
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