Add sys::Branch.last_migration (#7654)

`select sys::Branch { name, last_migration }` will list all branch names
with the names of their latest migrations. Note that `last_migration`
could be an empty set if the branch is empty.

edb/buildmeta.py

@@ -60,7 +60,7 @@
 # The merge conflict there is a nice reminder that you probably need
 # to write a patch in edb/pgsql/patches.py, and then you should preserve
 # the old value.
-EDGEDB_CATALOG_VERSION = 2024_08_23_00_00
+EDGEDB_CATALOG_VERSION = 2024_08_27_00_00
 EDGEDB_MAJOR_VERSION = 6
 
 

edb/lib/sys.edgeql

@@ -39,6 +39,7 @@ CREATE TYPE sys::Branch EXTENDING
     ALTER PROPERTY name {
         CREATE CONSTRAINT std::exclusive;
     };
+    CREATE PROPERTY last_migration-> std::str;
 };
 
 CREATE ALIAS sys::Database := sys::Branch;

edb/pgsql/dbops/databases.py

@@ -30,7 +30,32 @@
 from . import ddl
 
 
-class Database(base.DBObject):
+class AbstractDatabase(base.DBObject):
+    def get_type(self):
+        return 'DATABASE'
+
+    def is_shared(self) -> bool:
+        return True
+
+    def _get_id_expr(self) -> str:
+        raise NotImplementedError()
+
+    def get_oid(self) -> base.Query:
+        qry = textwrap.dedent(f'''\
+            SELECT
+                'pg_database'::regclass::oid AS classoid,
+                pg_database.oid AS objectoid,
+                0
+            FROM
+                pg_database
+            WHERE
+                datname = {self._get_id_expr()}
+        ''')
+
+        return base.Query(text=qry)
+
+
+class Database(AbstractDatabase):
     def __init__(
         self,
         name: str,
@@ -50,28 +75,11 @@ def __init__(
         self.lc_collate = lc_collate
         self.lc_ctype = lc_ctype
 
-    def get_type(self):
-        return 'DATABASE'
-
     def get_id(self):
         return qi(self.name)
 
-    def is_shared(self) -> bool:
-        return True
-
-    def get_oid(self) -> base.Query:
-        qry = textwrap.dedent(f'''\
-            SELECT
-                'pg_database'::regclass::oid AS classoid,
-                pg_database.oid AS objectoid,
-                0
-            FROM
-                pg_database
-            WHERE
-                datname = {ql(self.name)}
-        ''')
-
-        return base.Query(text=qry)
+    def _get_id_expr(self) -> str:
+        return ql(self.name)
 
 
 class DatabaseWithTenant(Database):
@@ -81,24 +89,19 @@ def __init__(
     ) -> None:
         super().__init__(name=name)
 
-    def get_id(self):
-        dyn_db = f"{V('edgedb')}.get_database_backend_name({ql(self.name)})"
-        return f"' || quote_ident({dyn_db}) || '"
+    def get_id(self) -> str:
+        return f"' || quote_ident({self._get_id_expr()}) || '"
 
-    def get_oid(self) -> base.Query:
-        qry = textwrap.dedent(f'''\
-            SELECT
-                'pg_database'::regclass::oid AS classoid,
-                pg_database.oid AS objectoid,
-                0
-            FROM
-                pg_database
-            WHERE
-                datname =
-                  {V("edgedb")}.get_database_backend_name({ql(self.name)})
-        ''')
+    def _get_id_expr(self) -> str:
+        return f'{V("edgedb")}.get_database_backend_name({ql(self.name)})'
 
-        return base.Query(text=qry)
+
+class CurrentDatabase(AbstractDatabase):
+    def get_id(self) -> str:
+        return f"' || quote_ident({self._get_id_expr()}) || '"
+
+    def _get_id_expr(self) -> str:
+        return 'current_database()'
 
 
 class DatabaseExists(base.Condition):

edb/pgsql/delta.py

@@ -7301,7 +7301,21 @@ def apply(
 
 
 class MigrationCommand(MetaCommand):
-    pass
+    def apply(
+        self,
+        schema: s_schema.Schema,
+        context: sd.CommandContext,
+    ) -> s_schema.Schema:
+        schema = super().apply(schema, context)
+        if last_mig := schema.get_last_migration():
+            last_mig_name = last_mig.get_name(schema).name
+        else:
+            last_mig_name = None
+        self.pgops.add(dbops.UpdateMetadata(
+            dbops.CurrentDatabase(),
+            {'last_migration': last_mig_name},
+        ))
+        return schema
 
 
 class CreateMigration(

edb/pgsql/metaschema.py

@@ -5098,6 +5098,7 @@ def _generate_branch_views(schema: s_schema.Schema) -> List[dbops.View]:
         ),
         'computed_fields': 'ARRAY[]::text[]',
         'builtin': "((d.description)->>'builtin')::bool",
+        'last_migration': "(d.description)->>'last_migration'",
     }
 
     view_query = f'''

tests/test_edgeql_data_migration.py

@@ -216,6 +216,7 @@ async def migrate(
                 explicit_modules=explicit_modules,
             )
             await self.fast_forward_describe_migration(user_input=user_input)
+        await self.assert_last_migration()
 
     async def interact(self, parts, check_complete=True):
         for part in parts:
@@ -243,6 +244,25 @@ async def interact(self, parts, check_complete=True):
                 'complete': True
             })
 
+    async def assert_last_migration(self):
+        last_name = await self.con.query_single(
+            '''
+            select assert_single(
+                sys::Branch.last_migration
+                    filter sys::Branch.name = sys::get_current_database());
+            '''
+        )
+        last_mig = await self.con.query_single(
+            '''
+            select assert_single(
+                schema::Migration { name } filter not exists .<parents);
+            '''
+        )
+        if last_mig:
+            self.assertEqual(last_mig.name, last_name)
+        else:
+            self.assertIsNone(last_name)
+
 
 class TestEdgeQLDataMigration(EdgeQLDataMigrationTestCase):
     async def test_edgeql_migration_simple_01(self):
@@ -12275,6 +12295,7 @@ async def test_edgeql_migration_reset_schema(self):
         self.assertEqual(len(res), 2)
 
         await self.con.query('reset schema to initial')
+        await self.assert_last_migration()
 
         res = await self.con.query('''
             select schema::ObjectType { name } filter .name ilike 'test::%'
@@ -12869,6 +12890,7 @@ async def assert_migration_history(self, exp_result):
         res = serutils.serialize(res)
         assert_data_shape.assert_data_shape(
             res, exp_result, self.fail)
+        await self.assert_last_migration()
 
 
 class TestEdgeQLMigrationRewrite(EdgeQLMigrationRewriteTestCase):