Adding 'sqlmigrate' command and quote_parameter to support it.

django/core/management/commands/sqlmigrate.py

+# encoding: utf8
+from __future__ import unicode_literals
+from optparse import make_option
+
+from django.core.management.base import BaseCommand, CommandError
+from django.db import connections, DEFAULT_DB_ALIAS
+from django.db.migrations.executor import MigrationExecutor
+from django.db.migrations.loader import AmbiguityError
+
+
+class Command(BaseCommand):
+
+    option_list = BaseCommand.option_list + (
+        make_option('--database', action='store', dest='database',
+            default=DEFAULT_DB_ALIAS, help='Nominates a database to create SQL for. '
+                'Defaults to the "default" database.'),
+        make_option('--backwards', action='store_true', dest='backwards',
+            default=False, help='Creates SQL to unapply the migration, rather than to apply it'),
+    )
+
+    help = "Prints the SQL statements for the named migration."
+
+    def handle(self, *args, **options):
+
+        # Get the database we're operating from
+        db = options.get('database')
+        connection = connections[db]
+
+        # Load up an executor to get all the migration data
+        executor = MigrationExecutor(connection)
+
+        # Resolve command-line arguments into a migration
+        if len(args) != 2:
+            raise CommandError("Wrong number of arguments (expecting 'sqlmigrate appname migrationname')")
+        else:
+            app_label, migration_name = args
+            if app_label not in executor.loader.migrated_apps:
+                raise CommandError("App '%s' does not have migrations" % app_label)
+            try:
+                migration = executor.loader.get_migration_by_prefix(app_label, migration_name)
+            except AmbiguityError:
+                raise CommandError("More than one migration matches '%s' in app '%s'. Please be more specific." % (app_label, migration_name))
+            except KeyError:
+                raise CommandError("Cannot find a migration matching '%s' from app '%s'. Is it in INSTALLED_APPS?" % (app_label, migration_name))
+            targets = [(app_label, migration.name)]
+
+        # Make a plan that represents just the requested migrations and show SQL
+        # for it
+        plan = [(executor.loader.graph.nodes[targets[0]], options.get("backwards", False))]
+        sql_statements = executor.collect_sql(plan)
+        for statement in sql_statements:
+            self.stdout.write(statement)

django/db/backends/__init__.py

@@ -521,7 +521,7 @@ class BaseDatabaseWrapper(object):
         """
         raise NotImplementedError
 
-    def schema_editor(self):
+    def schema_editor(self, *args, **kwargs):
         "Returns a new instance of this backend's SchemaEditor"
         raise NotImplementedError()
 
@@ -958,6 +958,15 @@ class BaseDatabaseOperations(object):
         """
         raise NotImplementedError()
 
+    def quote_parameter(self, value):
+        """
+        Returns a quoted version of the value so it's safe to use in an SQL
+        string. This should NOT be used to prepare SQL statements to send to
+        the database; it is meant for outputting SQL statements to a file
+        or the console for later execution by a developer/DBA.
+        """
+        raise NotImplementedError()
+
     def random_function_sql(self):
         """
         Returns an SQL expression that returns a random value.

django/db/backends/mysql/base.py

@@ -305,6 +305,11 @@ class DatabaseOperations(BaseDatabaseOperations):
             return name # Quoting once is enough.
         return "`%s`" % name
 
+    def quote_parameter(self, value):
+        # Inner import to allow module to fail to load gracefully
+        import MySQLdb.converters
+        return MySQLdb.escape(value, MySQLdb.converters.conversions)
+
     def random_function_sql(self):
         return 'RAND()'
 
@@ -518,9 +523,9 @@ class DatabaseWrapper(BaseDatabaseWrapper):
                         table_name, column_name, bad_row[1],
                         referenced_table_name, referenced_column_name))
 
-    def schema_editor(self):
+    def schema_editor(self, *args, **kwargs):
         "Returns a new instance of this backend's SchemaEditor"
-        return DatabaseSchemaEditor(self)
+        return DatabaseSchemaEditor(self, *args, **kwargs)
 
     def is_usable(self):
         try:

django/db/backends/oracle/base.py

@@ -320,6 +320,16 @@ WHEN (new.%(col_name)s IS NULL)
         name = name.replace('%', '%%')
         return name.upper()
 
+    def quote_parameter(self, value):
+        if isinstance(value, (datetime.date, datetime.time, datetime.datetime)):
+            return "'%s'" % value
+        elif isinstance(value, six.string_types):
+            return repr(value)
+        elif isinstance(value, bool):
+            return "1" if value else "0"
+        else:
+            return str(value)
+
     def random_function_sql(self):
         return "DBMS_RANDOM.RANDOM"
 
@@ -628,9 +638,9 @@ class DatabaseWrapper(BaseDatabaseWrapper):
                     six.reraise(utils.IntegrityError, utils.IntegrityError(*tuple(e.args)), sys.exc_info()[2])
                 raise
 
-    def schema_editor(self):
+    def schema_editor(self, *args, **kwargs):
         "Returns a new instance of this backend's SchemaEditor"
-        return DatabaseSchemaEditor(self)
+        return DatabaseSchemaEditor(self, *args, **kwargs)
 
     # Oracle doesn't support savepoint commits.  Ignore them.
     def _savepoint_commit(self, sid):

django/db/backends/oracle/schema.py

@@ -93,11 +93,4 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         return self.normalize_name(for_name + "_" + suffix)
 
     def prepare_default(self, value):
-        if isinstance(value, (datetime.date, datetime.time, datetime.datetime)):
-            return "'%s'" % value
-        elif isinstance(value, six.string_types):
-            return repr(value)
-        elif isinstance(value, bool):
-            return "1" if value else "0"
-        else:
-            return str(value)
+        return self.connection.ops.quote_parameter(value)

django/db/backends/postgresql_psycopg2/base.py

@@ -205,9 +205,9 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         else:
             return True
 
-    def schema_editor(self):
+    def schema_editor(self, *args, **kwargs):
         "Returns a new instance of this backend's SchemaEditor"
-        return DatabaseSchemaEditor(self)
+        return DatabaseSchemaEditor(self, *args, **kwargs)
 
     @cached_property
     def psycopg2_version(self):

django/db/backends/postgresql_psycopg2/operations.py

@@ -98,6 +98,11 @@ class DatabaseOperations(BaseDatabaseOperations):
             return name # Quoting once is enough.
         return '"%s"' % name
 
+    def quote_parameter(self, value):
+        # Inner import so backend fails nicely if it's not present
+        import psycopg2
+        return psycopg2.extensions.adapt(value)
+
     def set_time_zone_sql(self):
         return "SET TIME ZONE %s"
 

django/db/backends/schema.py

@@ -54,14 +54,17 @@ class BaseDatabaseSchemaEditor(object):
     sql_create_fk = "ALTER TABLE %(table)s ADD CONSTRAINT %(name)s FOREIGN KEY (%(column)s) REFERENCES %(to_table)s (%(to_column)s) DEFERRABLE INITIALLY DEFERRED"
     sql_delete_fk = "ALTER TABLE %(table)s DROP CONSTRAINT %(name)s"
 
-    sql_create_index = "CREATE INDEX %(name)s ON %(table)s (%(columns)s)%(extra)s;"
+    sql_create_index = "CREATE INDEX %(name)s ON %(table)s (%(columns)s)%(extra)s"
     sql_delete_index = "DROP INDEX %(name)s"
 
     sql_create_pk = "ALTER TABLE %(table)s ADD CONSTRAINT %(name)s PRIMARY KEY (%(columns)s)"
     sql_delete_pk = "ALTER TABLE %(table)s DROP CONSTRAINT %(name)s"
 
-    def __init__(self, connection):
+    def __init__(self, connection, collect_sql=False):
         self.connection = connection
+        self.collect_sql = collect_sql
+        if self.collect_sql:
+            self.collected_sql = []
 
     # State-managing methods
 
@@ -86,7 +89,10 @@ class BaseDatabaseSchemaEditor(object):
         cursor = self.connection.cursor()
         # Log the command we're running, then run it
         logger.debug("%s; (params %r)" % (sql, params))
-        cursor.execute(sql, params)
+        if self.collect_sql:
+            self.collected_sql.append((sql % map(self.connection.ops.quote_parameter, params)) + ";")
+        else:
+            cursor.execute(sql, params)
 
     def quote_name(self, name):
         return self.connection.ops.quote_name(name)

django/db/backends/sqlite3/base.py

@@ -214,6 +214,25 @@ class DatabaseOperations(BaseDatabaseOperations):
             return name # Quoting once is enough.
         return '"%s"' % name
 
+    def quote_parameter(self, value):
+        # Inner import to allow nice failure for backend if not present
+        import _sqlite3
+        try:
+            value = _sqlite3.adapt(value)
+        except _sqlite3.ProgrammingError:
+            pass
+        # Manual emulation of SQLite parameter quoting
+        if isinstance(value, six.integer_types):
+            return str(value)
+        elif isinstance(value, six.string_types):
+            return six.text_type(value)
+        elif isinstance(value, type(True)):
+            return str(int(value))
+        elif value is None:
+            return "NULL"
+        else:
+            raise ValueError("Cannot quote parameter value %r" % value)
+
     def no_limit_value(self):
         return -1
 
@@ -437,9 +456,9 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         """
         self.cursor().execute("BEGIN")
 
-    def schema_editor(self):
+    def schema_editor(self, *args, **kwargs):
         "Returns a new instance of this backend's SchemaEditor"
-        return DatabaseSchemaEditor(self)
+        return DatabaseSchemaEditor(self, *args, **kwargs)
 
 FORMAT_QMARK_REGEX = re.compile(r'(?<!%)%s')
 

django/db/backends/sqlite3/schema.py

@@ -55,7 +55,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         self.create_model(temp_model)
         # Copy data from the old table
         field_maps = list(mapping.items())
-        self.execute("INSERT INTO %s (%s) SELECT %s FROM %s;" % (
+        self.execute("INSERT INTO %s (%s) SELECT %s FROM %s" % (
             self.quote_name(temp_model._meta.db_table),
             ', '.join(x for x, y in field_maps),
             ', '.join(y for x, y in field_maps),
@@ -137,7 +137,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         # Make a new through table
         self.create_model(new_field.rel.through)
         # Copy the data across
-        self.execute("INSERT INTO %s (%s) SELECT %s FROM %s;" % (
+        self.execute("INSERT INTO %s (%s) SELECT %s FROM %s" % (
             self.quote_name(new_field.rel.through._meta.db_table),
             ', '.join([
                 "id",

django/db/migrations/executor.py

@@ -61,6 +61,22 @@ class MigrationExecutor(object):
             else:
                 self.unapply_migration(migration, fake=fake)
 
+    def collect_sql(self, plan):
+        """
+        Takes a migration plan and returns a list of collected SQL
+        statements that represent the best-efforts version of that plan.
+        """
+        statements = []
+        for migration, backwards in plan:
+            with self.connection.schema_editor(collect_sql=True) as schema_editor:
+                project_state = self.loader.graph.project_state((migration.app_label, migration.name), at_end=False)
+                if not backwards:
+                    migration.apply(project_state, schema_editor)
+                else:
+                    migration.unapply(project_state, schema_editor)
+                statements.extend(schema_editor.collected_sql)
+        return statements
+
     def apply_migration(self, migration, fake=False):
         """
         Runs a migration forwards.

docs/ref/django-admin.txt

@@ -993,6 +993,24 @@ Prints the CREATE INDEX SQL statements for the given app name(s).
 The :djadminopt:`--database` option can be used to specify the database for
 which to print the SQL.
 
+sqlmigrate <appname> <migrationname>
+------------------------------------
+
+.. django-admin:: sqlmigrate
+
+Prints the SQL for the named migration. This requires an active database
+connection, which it will use to resolve constraint names; this means you must
+generate the SQL against a copy of the database you wish to later apply it on.
+
+The :djadminopt:`--database` option can be used to specify the database for
+which to generate the SQL.
+
+.. django-admin-option:: --backwards
+
+By default, the SQL created is for running the migration in the forwards
+direction. Pass ``--backwards`` to generate the SQL for
+un-applying the migration instead.
+
 sqlsequencereset <appname appname ...>
 --------------------------------------
 

tests/migrations/test_commands.py

@@ -48,6 +48,20 @@ class MigrateTests(MigrationTestBase):
         self.assertTableNotExists("migrations_tribble")
         self.assertTableNotExists("migrations_book")
 
+    @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations"})
+    def test_sqlmigrate(self):
+        """
+        Makes sure that sqlmigrate does something.
+        """
+        # Test forwards. All the databases agree on CREATE TABLE, at least.
+        stdout = six.StringIO()
+        call_command("sqlmigrate", "migrations", "0001", stdout=stdout)
+        self.assertIn("create table", stdout.getvalue().lower())
+        # And backwards is a DROP TABLE
+        stdout = six.StringIO()
+        call_command("sqlmigrate", "migrations", "0001", stdout=stdout, backwards=True)
+        self.assertIn("drop table", stdout.getvalue().lower())
+
 
 class MakeMigrationsTests(MigrationTestBase):
     """