Fixed #28816 -- Prevented silencing data loss when decreasing CharField.max_length on PostgreSQL.
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@ -6,8 +6,6 @@ from django.db.backends.ddl_references import IndexColumns
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class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
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sql_alter_column_type = "ALTER COLUMN %(column)s TYPE %(type)s USING %(column)s::%(type)s"
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sql_create_sequence = "CREATE SEQUENCE %(sequence)s"
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sql_delete_sequence = "DROP SEQUENCE IF EXISTS %(sequence)s CASCADE"
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sql_set_sequence_max = "SELECT setval('%(sequence)s', MAX(%(column)s)) FROM %(table)s"
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@ -36,6 +34,11 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
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output.append(like_index_statement)
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return output
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def _field_data_type(self, field):
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if field.is_relation:
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return field.rel_db_type(self.connection)
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return self.connection.data_types[field.get_internal_type()]
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def _create_like_index_sql(self, model, field):
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"""
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Return the statement to create an index with varchar operator pattern
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@ -59,7 +62,11 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
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return None
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def _alter_column_type_sql(self, model, old_field, new_field, new_type):
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"""Make ALTER TYPE with SERIAL make sense."""
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self.sql_alter_column_type = 'ALTER COLUMN %(column)s TYPE %(type)s'
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# Cast when data type changed.
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if self._field_data_type(old_field) != self._field_data_type(new_field):
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self.sql_alter_column_type += ' USING %(column)s::%(type)s'
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# Make ALTER TYPE with SERIAL make sense.
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table = model._meta.db_table
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if new_type.lower() in ("serial", "bigserial"):
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column = new_field.column
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@ -21,6 +21,7 @@ from django.db.models.fields.related import (
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)
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from django.db.models.indexes import Index
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from django.db.transaction import TransactionManagementError, atomic
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from django.db.utils import DataError
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from django.test import (
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TransactionTestCase, skipIfDBFeature, skipUnlessDBFeature,
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)
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@ -803,6 +804,21 @@ class SchemaTests(TransactionTestCase):
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with connection.schema_editor() as editor:
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editor.alter_field(Author, old_field, new_field, strict=True)
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@unittest.skipUnless(connection.vendor == 'postgresql', 'PostgreSQL specific')
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def test_alter_char_field_decrease_length(self):
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# Create the table.
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with connection.schema_editor() as editor:
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editor.create_model(Author)
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Author.objects.create(name='x' * 255)
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# Change max_length of CharField.
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old_field = Author._meta.get_field('name')
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new_field = CharField(max_length=254)
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new_field.set_attributes_from_name('name')
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with connection.schema_editor() as editor:
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msg = 'value too long for type character varying(254)'
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with self.assertRaisesMessage(DataError, msg):
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editor.alter_field(Author, old_field, new_field, strict=True)
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def test_alter_textfield_to_null(self):
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"""
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#24307 - Should skip an alter statement on databases with
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