Reflect table can reflect table with no columns

The :meth:`_engine.Inspector.reflect_table` method now supports reflecting
tables that do not have user defined columns. This allows
:meth:`_schema.MetaData.reflect` to properly complete reflection on
databases that contain such tables.   Currently, only PostgreSQL is known
to support such a construct among the common database backends.

Fixes: #3247
Closes: #7118
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/7118
Pull-request-sha: cb8ce01957e9a1453290a7c2728af8c60ef55fa1

Change-Id: I906cebe17d13554d79086b92f3e1e51ffba3e818

diff --git a/doc/build/changelog/unreleased_14/3247.rst b/doc/build/changelog/unreleased_14/3247.rst
new file mode 100644 (file)
index 0000000..4ddb457
--- /dev/null
+++ b/doc/build/changelog/unreleased_14/3247.rst
@@ -0,0 +1,9 @@
+.. change::
+    :tags: engine, bug, postgresql
+    :tickets: 3247
+
+    The :meth:`_engine.Inspector.reflect_table` method now supports reflecting
+    tables that do not have user defined columns. This allows
+    :meth:`_schema.MetaData.reflect` to properly complete reflection on
+    databases that contain such tables.   Currently, only PostgreSQL is known
+    to support such a construct among the common database backends.

diff --git a/lib/sqlalchemy/engine/reflection.py b/lib/sqlalchemy/engine/reflection.py
index 715781b7a3d1f47186b582dcdd2301b800aa5232..113aa8ea06977d39bf43c2e7418c9f6884702923 100644 (file)
--- a/lib/sqlalchemy/engine/reflection.py
+++ b/lib/sqlalchemy/engine/reflection.py
@@ -784,8 +784,9 @@ class Inspector(object):
                 cols_by_orig_name,
             )
 
-        if not found_table:
-            raise exc.NoSuchTableError(table.name)
+        # NOTE: support tables/views with no columns
+        if not found_table and not self.has_table(table_name, schema):
+            raise exc.NoSuchTableError(table_name)
 
         self._reflect_pk(
             table_name, schema, table, cols_by_orig_name, exclude_columns

diff --git a/lib/sqlalchemy/testing/requirements.py b/lib/sqlalchemy/testing/requirements.py
index a546e1febc064a9cdaad8bc606220799d0c70571..f8b5dd6062ac75df67b631ffd11bb8b705a93f18 100644 (file)
--- a/lib/sqlalchemy/testing/requirements.py
+++ b/lib/sqlalchemy/testing/requirements.py
@@ -589,8 +589,16 @@ class SuiteRequirements(Requirements):
 
     @property
     def table_reflection(self):
+        """target database has general support for table reflection"""
         return exclusions.open()
 
+    @property
+    def reflect_tables_no_columns(self):
+        """target database supports creation and reflection of tables with no
+        columns, or at least tables that seem to have no columns."""
+
+        return exclusions.closed()
+
     @property
     def comment_reflection(self):
         return exclusions.closed()

diff --git a/lib/sqlalchemy/testing/suite/test_reflection.py b/lib/sqlalchemy/testing/suite/test_reflection.py
index 916d74db317cdb685013883b25ea5d0126957712..88189c2d95c7d8d4144c205984be5f81ed083a4a 100644 (file)
--- a/lib/sqlalchemy/testing/suite/test_reflection.py
+++ b/lib/sqlalchemy/testing/suite/test_reflection.py
@@ -1063,6 +1063,61 @@ class ComponentReflectionTest(fixtures.TablesTest):
             assert id_.get("autoincrement", True)
 
 
+class TableNoColumnsTest(fixtures.TestBase):
+    __requires__ = ("reflect_tables_no_columns",)
+    __backend__ = True
+
+    @testing.fixture
+    def table_no_columns(self, connection, metadata):
+        Table("empty", metadata)
+        metadata.create_all(connection)
+
+    @testing.fixture
+    def view_no_columns(self, connection, metadata):
+        Table("empty", metadata)
+        metadata.create_all(connection)
+
+        Table("empty", metadata)
+        event.listen(
+            metadata,
+            "after_create",
+            DDL("CREATE VIEW empty_v AS SELECT * FROM empty"),
+        )
+
+        # for transactional DDL the transaction is rolled back before this
+        # drop statement is invoked
+        event.listen(
+            metadata, "before_drop", DDL("DROP VIEW IF EXISTS empty_v")
+        )
+        metadata.create_all(connection)
+
+    @testing.requires.reflect_tables_no_columns
+    def test_reflect_table_no_columns(self, connection, table_no_columns):
+        t2 = Table("empty", MetaData(), autoload_with=connection)
+        eq_(list(t2.c), [])
+
+    @testing.requires.reflect_tables_no_columns
+    def test_get_columns_table_no_columns(self, connection, table_no_columns):
+        eq_(inspect(connection).get_columns("empty"), [])
+
+    @testing.requires.reflect_tables_no_columns
+    def test_reflect_incl_table_no_columns(self, connection, table_no_columns):
+        m = MetaData()
+        m.reflect(connection)
+        assert set(m.tables).intersection(["empty"])
+
+    @testing.requires.views
+    @testing.requires.reflect_tables_no_columns
+    def test_reflect_view_no_columns(self, connection, view_no_columns):
+        t2 = Table("empty_v", MetaData(), autoload_with=connection)
+        eq_(list(t2.c), [])
+
+    @testing.requires.views
+    @testing.requires.reflect_tables_no_columns
+    def test_get_columns_view_no_columns(self, connection, view_no_columns):
+        eq_(inspect(connection).get_columns("empty_v"), [])
+
+
 class ComponentReflectionTestExtra(fixtures.TestBase):
 
     __backend__ = True
@@ -1641,6 +1696,7 @@ class CompositeKeyReflectionTest(fixtures.TablesTest):
 __all__ = (
     "ComponentReflectionTest",
     "ComponentReflectionTestExtra",
+    "TableNoColumnsTest",
     "QuotedNameArgumentTest",
     "HasTableTest",
     "HasIndexTest",

diff --git a/test/requirements.py b/test/requirements.py
index 721bb8ba376ddf8b951746e54ba596e457185168..7efd6cbd50da4a289457656281ed4fba619cf416 100644 (file)
--- a/test/requirements.py
+++ b/test/requirements.py
@@ -1805,3 +1805,8 @@ class DefaultRequirements(SuiteRequirements):
     @property
     def autoincrement_without_sequence(self):
         return skip_if("oracle")
+
+    @property
+    def reflect_tables_no_columns(self):
+        # so far sqlite, mariadb, mysql don't support this
+        return only_on(["postgresql"])