Remove connections scoped to schema

It's too tricky to get this right. It'll lead to surprises because:


1. It breaks with transaction pooling.
2. Interaction with `SET LOCAL` is strange. A `SET` command after
a `SET LOCAL` overrides it.

I already shot myself in the foot twice since implementing this.

Author: Photonios

docs/source/schemas.rst

@@ -153,36 +153,3 @@ The ``public`` schema cannot be dropped. This is a Postgres built-in and it is a
 
    schema = PostgresSchema.drop("myprefix")
    schema = PostgresSchema.drop("myprefix", cascade=True)
-
-
-Executing queries within a schema
----------------------------------
-
-By default, a connection operates in the ``public`` schema. The schema offers a connection scoped to that schema that sets the Postgres ``search_path`` to only search within that schema.
-
-.. warning::
-
-   This can be abused to manage Django models in a custom schema. This is not a supported workflow and there might be unexpected issues from attempting to do so.
-
-.. warning::
-
-   Do not use this in the following scenarios:
-
-    1. You access the connection from multiple threads. Scoped connections are **NOT** thread safe.
-
-    2. The underlying database connection is passed through a connection pooler in transaction pooling mode.
-
-.. code-block:: python
-
-   from psqlextra.schema import PostgresSchema
-
-   schema = PostgresSchema.create("myschema")
-
-   with schema.connection.cursor() as cursor:
-       # table gets created within the `myschema` schema, without
-       # explicitly specifying the schema name
-       cursor.execute("CREATE TABLE mytable AS SELECT 'hello'")
-
-    with schema.connection.schema_editor() as schema_editor:
-        # creates a table for the model within the schema
-        schema_editor.create_model(MyModel)

psqlextra/schema.py

@@ -2,43 +2,11 @@
 
 from contextlib import contextmanager
 
-import wrapt
-
 from django.core.exceptions import SuspiciousOperation, ValidationError
 from django.db import DEFAULT_DB_ALIAS, connections, transaction
-from django.db.backends.base.base import BaseDatabaseWrapper
-from django.db.backends.utils import CursorWrapper
 from django.utils import timezone
 
 
-class PostgresSchemaConnectionWrapper(wrapt.ObjectProxy):
-    """Wraps a Django database connection and ensures that each cursor operates
-    within the specified schema."""
-
-    def __init__(self, connection, schema) -> None:
-        super().__init__(connection)
-
-        self._self_schema = schema
-
-    @contextmanager
-    def schema_editor(self):
-        with self.__wrapped__.schema_editor() as schema_editor:
-            schema_editor.connection = self
-            yield schema_editor
-
-    @contextmanager
-    def cursor(self) -> CursorWrapper:
-        schema = self._self_schema
-
-        with self.__wrapped__.cursor() as cursor:
-            quoted_name = self.ops.quote_name(schema.name)
-            cursor.execute(f"SET search_path = {quoted_name}")
-            try:
-                yield cursor
-            finally:
-                cursor.execute("SET search_path TO DEFAULT")
-
-
 class PostgresSchema:
     """Represents a Postgres schema.
 
@@ -191,20 +159,6 @@ def delete(self, *, cascade: bool = False) -> None:
         with connections[self.using].schema_editor() as schema_editor:
             schema_editor.delete_schema(self.name, cascade=cascade)
 
-    @property
-    def connection(self) -> BaseDatabaseWrapper:
-        """Obtains a database connection scoped to this schema.
-
-        Do not use this in the following scenarios:
-
-            1. You access the connection from multiple threads. Scoped
-            connections are NOT thread safe.
-            2. The underlying database connection is passed through a
-            connection pooler in transaction pooling mode.
-        """
-
-        return PostgresSchemaConnectionWrapper(connections[self.using], self)
-
     @classmethod
     def _verify_generated_name_length(cls, prefix: str, suffix: str) -> None:
         max_prefix_length = cls.NAME_MAX_LENGTH - len(suffix)

tests/test_schema.py

@@ -1,4 +1,3 @@
-import uuid
 
 import freezegun
 import pytest
@@ -136,7 +135,7 @@ def test_postgres_schema_delete_not_empty():
     schema = PostgresSchema.create("test")
     assert _does_schema_exist(schema.name)
 
-    with schema.connection.cursor() as cursor:
+    with connection.cursor() as cursor:
         cursor.execute("CREATE TABLE test.bla AS SELECT 'hello'")
 
     with pytest.raises(InternalError) as exc_info:
@@ -150,96 +149,14 @@ def test_postgres_schema_delete_cascade_not_empty():
     schema = PostgresSchema.create("test")
     assert _does_schema_exist(schema.name)
 
-    with schema.connection.cursor() as cursor:
+    with connection.cursor() as cursor:
         cursor.execute("CREATE TABLE test.bla AS SELECT 'hello'")
 
     schema.delete(cascade=True)
     assert not _does_schema_exist(schema.name)
 
 
-def test_postgres_schema_connection():
-    schema = PostgresSchema.create("test")
-
-    with schema.connection.cursor() as cursor:
-        # Creating a table without specifying the schema should create
-        # it in our schema and we should be able to select from it without
-        # specifying the schema.
-        cursor.execute("CREATE TABLE myschematable AS SELECT 'myschema'")
-        cursor.execute("SELECT * FROM myschematable")
-        assert cursor.fetchone() == ("myschema",)
-
-        # Proof that the table was created in our schema even though we
-        # never explicitly told it to do so.
-        cursor.execute(
-            "SELECT table_schema FROM information_schema.tables WHERE table_name = %s",
-            ("myschematable",),
-        )
-        assert cursor.fetchone() == (schema.name,)
-
-        # Creating a table in another schema, we should not be able
-        # to select it without specifying the schema since our
-        # schema scoped connection only looks at our schema by default.
-        cursor.execute(
-            "CREATE TABLE public.otherschematable AS SELECT 'otherschema'"
-        )
-        with pytest.raises(ProgrammingError) as exc_info:
-            cursor.execute("SELECT * FROM otherschematable")
-
-        cursor.execute("ROLLBACK")
-
-        pg_error = extract_postgres_error(exc_info.value)
-        assert pg_error.pgcode == errorcodes.UNDEFINED_TABLE
-
-
-def test_postgres_schema_connection_does_not_affect_default():
-    schema = PostgresSchema.create("test")
-
-    with schema.connection.cursor() as cursor:
-        cursor.execute("SHOW search_path")
-        assert cursor.fetchone() == ("test",)
-
-    with connection.cursor() as cursor:
-        cursor.execute("SHOW search_path")
-        assert cursor.fetchone() == ('"$user", public',)
-
-
-@pytest.mark.django_db(transaction=True)
-def test_postgres_schema_connection_does_not_affect_default_after_throw():
-    schema = PostgresSchema.create(str(uuid.uuid4()))
-
-    with pytest.raises(ProgrammingError):
-        with schema.connection.cursor() as cursor:
-            cursor.execute("COMMIT")
-            cursor.execute("SELECT frombadtable")
-
-    with connection.cursor() as cursor:
-        cursor.execute("ROLLBACK")
-        cursor.execute("SHOW search_path")
-        assert cursor.fetchone() == ('"$user", public',)
-
-
-def test_postgres_schema_connection_schema_editor():
-    schema = PostgresSchema.create("test")
-
-    with schema.connection.schema_editor() as schema_editor:
-        with schema_editor.connection.cursor() as cursor:
-            cursor.execute("SHOW search_path")
-            assert cursor.fetchone() == ("test",)
-
-    with connection.cursor() as cursor:
-        cursor.execute("SHOW search_path")
-        assert cursor.fetchone() == ('"$user", public',)
-
-
-def test_postgres_schema_connection_does_not_catch():
-    schema = PostgresSchema.create("test")
-
-    with pytest.raises(ValueError):
-        with schema.connection.cursor():
-            raise ValueError("test")
-
-
-def test_postgres_schema_connection_no_delete_default():
+def test_postgres_schema_no_delete_default():
     with pytest.raises(SuspiciousOperation):
         PostgresSchema.default.delete()
 
@@ -261,17 +178,21 @@ def test_postgres_temporary_schema():
 def test_postgres_temporary_schema_not_empty():
     with pytest.raises(InternalError) as exc_info:
         with postgres_temporary_schema("temp") as schema:
-            with schema.connection.cursor() as cursor:
-                cursor.execute("CREATE TABLE mytable AS SELECT 'hello world'")
+            with connection.cursor() as cursor:
+                cursor.execute(
+                    f"CREATE TABLE {schema.name}.mytable AS SELECT 'hello world'"
+                )
 
     pg_error = extract_postgres_error(exc_info.value)
     assert pg_error.pgcode == errorcodes.DEPENDENT_OBJECTS_STILL_EXIST
 
 
 def test_postgres_temporary_schema_not_empty_cascade():
     with postgres_temporary_schema("temp", cascade=True) as schema:
-        with schema.connection.cursor() as cursor:
-            cursor.execute("CREATE TABLE mytable AS SELECT 'hello world'")
+        with connection.cursor() as cursor:
+            cursor.execute(
+                f"CREATE TABLE {schema.name}.mytable AS SELECT 'hello world'"
+            )
 
     assert not _does_schema_exist(schema.name)