Fixed #26682 -- Added support for Oracle identity columns.

Thanks Shai Berger and Tim Graham for reviews.

6 files changed, 168 insertions, 79 deletions

diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index c3cb1143cc..7e338d690f 100644
--- a/django/db/backends/base/schema.py
+++ b/django/db/backends/base/schema.py
@@ -710,14 +710,7 @@ class BaseDatabaseSchemaEditor:
         # will always come along and replace it.
         if not old_field.primary_key and new_field.primary_key:
             # First, drop the old PK
-            constraint_names = self._constraint_names(model, primary_key=True)
-            if strict and len(constraint_names) != 1:
-                raise ValueError("Found wrong number (%s) of PK constraints for %s" % (
-                    len(constraint_names),
-                    model._meta.db_table,
-                ))
-            for constraint_name in constraint_names:
-                self.execute(self._delete_constraint_sql(self.sql_delete_pk, model, constraint_name))
+            self._delete_primary_key(model, strict)
             # Make the new one
             self.execute(
                 self.sql_create_pk % {
@@ -978,3 +971,13 @@ class BaseDatabaseSchemaEditor:
                     continue
                 result.append(name)
         return result
+
+    def _delete_primary_key(self, model, strict=False):
+        constraint_names = self._constraint_names(model, primary_key=True)
+        if strict and len(constraint_names) != 1:
+            raise ValueError('Found wrong number (%s) of PK constraints for %s' % (
+                len(constraint_names),
+                model._meta.db_table,
+            ))
+        for constraint_name in constraint_names:
+            self.execute(self._delete_constraint_sql(self.sql_delete_pk, model, constraint_name))
diff --git a/django/db/backends/oracle/base.py b/django/db/backends/oracle/base.py
index 783a959e94..2493bd791f 100644
--- a/django/db/backends/oracle/base.py
+++ b/django/db/backends/oracle/base.py
@@ -82,8 +82,8 @@ class DatabaseWrapper(BaseDatabaseWrapper):
     # Any format strings starting with "qn_" are quoted before being used in the
     # output (the "qn_" prefix is stripped before the lookup is performed.
     data_types = {
-        'AutoField': 'NUMBER(11)',
-        'BigAutoField': 'NUMBER(19)',
+        'AutoField': 'NUMBER(11) GENERATED BY DEFAULT ON NULL AS IDENTITY',
+        'BigAutoField': 'NUMBER(19) GENERATED BY DEFAULT ON NULL AS IDENTITY',
         'BinaryField': 'BLOB',
         'BooleanField': 'NUMBER(1)',
         'CharField': 'NVARCHAR2(%(max_length)s)',
diff --git a/django/db/backends/oracle/operations.py b/django/db/backends/oracle/operations.py
index 35b17408bf..992d7810b4 100644
--- a/django/db/backends/oracle/operations.py
+++ b/django/db/backends/oracle/operations.py
@@ -29,12 +29,22 @@ class DatabaseOperations(BaseDatabaseOperations):
 DECLARE
     table_value integer;
     seq_value integer;
+    seq_name user_tab_identity_cols.sequence_name%%TYPE;
 BEGIN
+    BEGIN
+        SELECT sequence_name INTO seq_name FROM user_tab_identity_cols
+        WHERE  table_name = '%(table_name)s' AND
+               column_name = '%(column_name)s';
+        EXCEPTION WHEN NO_DATA_FOUND THEN
+            seq_name := '%(no_autofield_sequence_name)s';
+    END;
+
     SELECT NVL(MAX(%(column)s), 0) INTO table_value FROM %(table)s;
     SELECT NVL(last_number - cache_size, 0) INTO seq_value FROM user_sequences
-           WHERE sequence_name = '%(sequence)s';
+           WHERE sequence_name = seq_name;
     WHILE table_value > seq_value LOOP
-        seq_value := "%(sequence)s".nextval;
+        EXECUTE IMMEDIATE 'SELECT "'||seq_name||'".nextval FROM DUAL'
+        INTO seq_value;
     END LOOP;
 END;
 /"""
@@ -43,37 +53,6 @@ END;
         super().__init__(*args, **kwargs)
         self.set_operators['difference'] = 'MINUS'
 
-    def autoinc_sql(self, table, column):
-        # To simulate auto-incrementing primary keys in Oracle, we have to
-        # create a sequence and a trigger.
-        args = {
-            'sq_name': self._get_sequence_name(table),
-            'tr_name': self._get_trigger_name(table),
-            'tbl_name': self.quote_name(table),
-            'col_name': self.quote_name(column),
-        }
-        sequence_sql = """
-DECLARE
-    i INTEGER;
-BEGIN
-    SELECT COUNT(1) INTO i FROM USER_SEQUENCES
-        WHERE SEQUENCE_NAME = '%(sq_name)s';
-    IF i = 0 THEN
-        EXECUTE IMMEDIATE 'CREATE SEQUENCE "%(sq_name)s"';
-    END IF;
-END;
-/""" % args
-        trigger_sql = """
-CREATE OR REPLACE TRIGGER "%(tr_name)s"
-BEFORE INSERT ON %(tbl_name)s
-FOR EACH ROW
-WHEN (new.%(col_name)s IS NULL)
-    BEGIN
-        :new.%(col_name)s := "%(sq_name)s".nextval;
-    END;
-/""" % args
-        return sequence_sql, trigger_sql
-
     def cache_key_culling_sql(self):
         return """
             SELECT cache_key
@@ -253,7 +232,7 @@ WHEN (new.%(col_name)s IS NULL)
         return super().last_executed_query(cursor, statement, params)
 
     def last_insert_id(self, cursor, table_name, pk_name):
-        sq_name = self._get_sequence_name(table_name)
+        sq_name = self._get_sequence_name(cursor, strip_quotes(table_name), pk_name)
         cursor.execute('"%s".currval' % sq_name)
         return cursor.fetchone()[0]
 
@@ -397,13 +376,15 @@ WHEN (new.%(col_name)s IS NULL)
     def sequence_reset_by_name_sql(self, style, sequences):
         sql = []
         for sequence_info in sequences:
-            sequence_name = self._get_sequence_name(sequence_info['table'])
-            table_name = self.quote_name(sequence_info['table'])
-            column_name = self.quote_name(sequence_info['column'] or 'id')
+            no_autofield_sequence_name = self._get_no_autofield_sequence_name(sequence_info['table'])
+            table = self.quote_name(sequence_info['table'])
+            column = self.quote_name(sequence_info['column'] or 'id')
             query = self._sequence_reset_sql % {
-                'sequence': sequence_name,
-                'table': table_name,
-                'column': column_name,
+                'no_autofield_sequence_name': no_autofield_sequence_name,
+                'table': table,
+                'column': column,
+                'table_name': strip_quotes(table),
+                'column_name': strip_quotes(column),
             }
             sql.append(query)
         return sql
@@ -415,23 +396,31 @@ WHEN (new.%(col_name)s IS NULL)
         for model in model_list:
             for f in model._meta.local_fields:
                 if isinstance(f, models.AutoField):
-                    table_name = self.quote_name(model._meta.db_table)
-                    sequence_name = self._get_sequence_name(model._meta.db_table)
-                    column_name = self.quote_name(f.column)
-                    output.append(query % {'sequence': sequence_name,
-                                           'table': table_name,
-                                           'column': column_name})
+                    no_autofield_sequence_name = self._get_no_autofield_sequence_name(model._meta.db_table)
+                    table = self.quote_name(model._meta.db_table)
+                    column = self.quote_name(f.column)
+                    output.append(query % {
+                        'no_autofield_sequence_name': no_autofield_sequence_name,
+                        'table': table,
+                        'column': column,
+                        'table_name': strip_quotes(table),
+                        'column_name': strip_quotes(column),
+                    })
                     # Only one AutoField is allowed per model, so don't
                     # continue to loop
                     break
             for f in model._meta.many_to_many:
                 if not f.remote_field.through:
-                    table_name = self.quote_name(f.m2m_db_table())
-                    sequence_name = self._get_sequence_name(f.m2m_db_table())
-                    column_name = self.quote_name('id')
-                    output.append(query % {'sequence': sequence_name,
-                                           'table': table_name,
-                                           'column': column_name})
+                    no_autofield_sequence_name = self._get_no_autofield_sequence_name(f.m2m_db_table())
+                    table = self.quote_name(f.m2m_db_table())
+                    column = self.quote_name('id')
+                    output.append(query % {
+                        'no_autofield_sequence_name': no_autofield_sequence_name,
+                        'table': table,
+                        'column': column,
+                        'table_name': strip_quotes(table),
+                        'column_name': 'ID',
+                    })
         return output
 
     def start_transaction_sql(self):
@@ -512,15 +501,23 @@ WHEN (new.%(col_name)s IS NULL)
             return 'POWER(%s)' % ','.join(sub_expressions)
         return super().combine_expression(connector, sub_expressions)
 
-    def _get_sequence_name(self, table):
+    def _get_no_autofield_sequence_name(self, table):
+        """
+        Manually created sequence name to keep backward compatibility for
+        AutoFields that aren't Oracle identity columns.
+        """
         name_length = self.max_name_length() - 3
         sequence_name = '%s_SQ' % strip_quotes(table)
         return truncate_name(sequence_name, name_length).upper()
 
-    def _get_trigger_name(self, table):
-        name_length = self.max_name_length() - 3
-        trigger_name = '%s_TR' % strip_quotes(table)
-        return truncate_name(trigger_name, name_length).upper()
+    def _get_sequence_name(self, cursor, table, pk_name):
+        cursor.execute("""
+            SELECT sequence_name
+            FROM user_tab_identity_cols
+            WHERE table_name = UPPER(%s)
+            AND column_name = UPPER(%s)""", [table, pk_name])
+        row = cursor.fetchone()
+        return self._get_no_autofield_sequence_name(table) if row is None else row[0]
 
     def bulk_insert_sql(self, fields, placeholder_rows):
         query = []
@@ -528,13 +525,20 @@ WHEN (new.%(col_name)s IS NULL)
             select = []
             for i, placeholder in enumerate(row):
                 # A model without any fields has fields=[None].
-                if not fields[i]:
-                    select.append(placeholder)
-                else:
+                if fields[i]:
                     internal_type = getattr(fields[i], 'target_field', fields[i]).get_internal_type()
-                    select.append(BulkInsertMapper.types.get(internal_type, '%s') % placeholder)
+                    placeholder = BulkInsertMapper.types.get(internal_type, '%s') % placeholder
+                # Add columns aliases to the first select to avoid "ORA-00918:
+                # column ambiguously defined" when two or more columns in the
+                # first select have the same value.
+                if not query:
+                    placeholder = '%s col_%s' % (placeholder, i)
+                select.append(placeholder)
             query.append('SELECT %s FROM DUAL' % ', '.join(select))
-        return ' UNION ALL '.join(query)
+        # Bulk insert to tables with Oracle identity columns causes Oracle to
+        # add sequence.nextval to it. Sequence.nextval cannot be used with the
+        # UNION operator. To prevent incorrect SQL, move UNION to a subquery.
+        return 'SELECT * FROM (%s)' % ' UNION ALL '.join(query)
 
     def subtract_temporals(self, internal_type, lhs, rhs):
         if internal_type == 'DateField':
diff --git a/django/db/backends/oracle/schema.py b/django/db/backends/oracle/schema.py
index 5b1ae0adcb..742ff39f2c 100644
--- a/django/db/backends/oracle/schema.py
+++ b/django/db/backends/oracle/schema.py
@@ -31,10 +31,17 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         else:
             return str(value)
 
+    def remove_field(self, model, field):
+        # If the column is an identity column, drop the identity before
+        # removing the field.
+        if self._is_identity_column(model._meta.db_table, field.column):
+            self._drop_identity(model._meta.db_table, field.column)
+        super().remove_field(model, field)
+
     def delete_model(self, model):
         # Run superclass action
         super().delete_model(model)
-        # Clean up any autoincrement trigger
+        # Clean up manually created sequence.
         self.execute("""
             DECLARE
                 i INTEGER;
@@ -45,7 +52,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                     EXECUTE IMMEDIATE 'DROP SEQUENCE "%(sq_name)s"';
                 END IF;
             END;
-        /""" % {'sq_name': self.connection.ops._get_sequence_name(model._meta.db_table)})
+        /""" % {'sq_name': self.connection.ops._get_no_autofield_sequence_name(model._meta.db_table)})
 
     def alter_field(self, model, old_field, new_field, strict=False):
         try:
@@ -56,6 +63,16 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             # SQLite-ish workaround
             if 'ORA-22858' in description or 'ORA-22859' in description:
                 self._alter_field_type_workaround(model, old_field, new_field)
+            # If an identity column is changing to a non-numeric type, drop the
+            # identity first.
+            elif 'ORA-30675' in description:
+                self._drop_identity(model._meta.db_table, old_field.column)
+                self.alter_field(model, old_field, new_field, strict)
+            # If a primary key column is changing to an identity column, drop
+            # the primary key first.
+            elif 'ORA-30673' in description and old_field.primary_key:
+                self._delete_primary_key(model, strict=True)
+                self._alter_field_type_workaround(model, old_field, new_field)
             else:
                 raise
 
@@ -63,7 +80,9 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         """
         Oracle refuses to change from some type to other type.
         What we need to do instead is:
-        - Add a nullable version of the desired field with a temporary name
+        - Add a nullable version of the desired field with a temporary name. If
+          the new column is an auto field, then the temporary column can't be
+          nullable.
         - Update the table to transfer values from old to new
         - Drop old column
         - Rename the new column and possibly drop the nullable property
@@ -71,7 +90,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         # Make a new field that's like the new one but with a temporary
         # column name.
         new_temp_field = copy.deepcopy(new_field)
-        new_temp_field.null = True
+        new_temp_field.null = (new_field.get_internal_type() not in ('AutoField', 'BigAutoField'))
         new_temp_field.column = self._generate_temp_name(new_field.column)
         # Add it
         self.add_field(model, new_temp_field)
@@ -126,3 +145,21 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         if db_type is not None and db_type.lower() in self.connection._limited_data_types:
             return False
         return create_index
+
+    def _is_identity_column(self, table_name, column_name):
+        with self.connection.cursor() as cursor:
+            cursor.execute("""
+                SELECT
+                    CASE WHEN identity_column = 'YES' THEN 1 ELSE 0 END
+                FROM user_tab_cols
+                WHERE table_name = %s AND
+                      column_name = %s
+            """, [self.normalize_name(table_name), self.normalize_name(column_name)])
+            row = cursor.fetchone()
+            return row[0] if row else False
+
+    def _drop_identity(self, table_name, column_name):
+        self.execute('ALTER TABLE %(table)s MODIFY %(column)s DROP IDENTITY' % {
+            'table': self.quote_name(table_name),
+            'column': self.quote_name(column_name),
+        })
diff --git a/docs/releases/2.0.txt b/docs/releases/2.0.txt
index 0d2b2d77ed..6666f6d1d5 100644
--- a/docs/releases/2.0.txt
+++ b/docs/releases/2.0.txt
@@ -206,6 +206,11 @@ Models
 * The new :class:`~django.db.models.functions.StrIndex` database function
   finds the starting index of a string inside another string.
 
+* On Oracle, ``AutoField`` and ``BigAutoField`` are now created as `identity
+  columns`_.
+
+  .. _`identity columns`: https://docs.oracle.com/database/121/DRDAA/migr_tools_feat.htm#DRDAA109
+
 Requests and Responses
 ~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index 1642feb3fe..d6773afa00 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -10,9 +10,9 @@ from django.db import (
 from django.db.models import Model
 from django.db.models.deletion import CASCADE, PROTECT
 from django.db.models.fields import (
-    AutoField, BigIntegerField, BinaryField, BooleanField, CharField,
-    DateField, DateTimeField, IntegerField, PositiveIntegerField, SlugField,
-    TextField, TimeField,
+    AutoField, BigAutoField, BigIntegerField, BinaryField, BooleanField,
+    CharField, DateField, DateTimeField, IntegerField, PositiveIntegerField,
+    SlugField, TextField, TimeField,
 )
 from django.db.models.fields.related import (
     ForeignKey, ForeignObject, ManyToManyField, OneToOneField,
@@ -532,6 +532,30 @@ class SchemaTests(TransactionTestCase):
         self.assertEqual(columns['name'][0], "TextField")
         self.assertEqual(bool(columns['name'][1][6]), bool(connection.features.interprets_empty_strings_as_nulls))
 
+    def test_alter_auto_field_to_integer_field(self):
+        # Create the table
+        with connection.schema_editor() as editor:
+            editor.create_model(Author)
+        # Change AutoField to IntegerField
+        old_field = Author._meta.get_field('id')
+        new_field = IntegerField(primary_key=True)
+        new_field.set_attributes_from_name('id')
+        new_field.model = Author
+        with connection.schema_editor() as editor:
+            editor.alter_field(Author, old_field, new_field, strict=True)
+
+    def test_alter_auto_field_to_char_field(self):
+        # Create the table
+        with connection.schema_editor() as editor:
+            editor.create_model(Author)
+        # Change AutoField to CharField
+        old_field = Author._meta.get_field('id')
+        new_field = CharField(primary_key=True, max_length=50)
+        new_field.set_attributes_from_name('id')
+        new_field.model = Author
+        with connection.schema_editor() as editor:
+            editor.alter_field(Author, old_field, new_field, strict=True)
+
     def test_alter_text_field(self):
         # Regression for "BLOB/TEXT column 'info' can't have a default value")
         # on MySQL.
@@ -1003,6 +1027,22 @@ class SchemaTests(TransactionTestCase):
         with connection.schema_editor() as editor:
             editor.alter_field(IntegerPK, old_field, new_field, strict=True)
 
+    def test_alter_int_pk_to_bigautofield_pk(self):
+        """
+        Should be able to rename an IntegerField(primary_key=True) to
+        BigAutoField(primary_key=True).
+        """
+        with connection.schema_editor() as editor:
+            editor.create_model(IntegerPK)
+
+        old_field = IntegerPK._meta.get_field('i')
+        new_field = BigAutoField(primary_key=True)
+        new_field.model = IntegerPK
+        new_field.set_attributes_from_name('i')
+
+        with connection.schema_editor() as editor:
+            editor.alter_field(IntegerPK, old_field, new_field, strict=True)
+
     def test_alter_int_pk_to_int_unique(self):
         """
         Should be able to rename an IntegerField(primary_key=True) to