feat: add Database.list_tables method (#219)

* feat: add `Database.list_tables` method

* update docs, add tests

* remove numeric from get_schema test

The NUMERIC column is not included in the emulator system tests.

* add unit tests

* add docs for table api and usage

* fix link to Field class

* typo in table constructor docs

* add reload and exists methods

* feat: add table method to database

* update usage docs to use factory method

* address warning in GitHub UI for sphinx header

* Update docs/table-usage.rst

Co-authored-by: larkee <[email protected]>

Author: tswast

docs/api-reference.rst

@@ -10,6 +10,7 @@ Most likely, you will be interacting almost exclusively with these:
     client-api
     instance-api
     database-api
+    table-api
     session-api
     keyset-api
     snapshot-api

docs/index.rst

@@ -11,6 +11,7 @@ Usage Documentation
   client-usage
   instance-usage
   database-usage
+  table-usage
   batch-usage
   snapshot-usage
   transaction-usage

docs/table-api.rst

@@ -0,0 +1,6 @@
+Table API
+=========
+
+.. automodule:: google.cloud.spanner_v1.table
+  :members:
+  :show-inheritance:

docs/table-usage.rst

@@ -0,0 +1,47 @@
+Table Admin
+===========
+
+After creating an :class:`~google.cloud.spanner_v1.database.Database`, you can
+interact with individual tables for that instance.
+
+
+List Tables
+-----------
+
+To iterate over all existing tables for an database, use its
+:meth:`~google.cloud.spanner_v1.database.Database.list_tables` method:
+
+.. code:: python
+
+    for table in database.list_tables():
+        # `table` is a `Table` object.
+
+This method yields :class:`~google.cloud.spanner_v1.table.Table` objects.
+
+
+Table Factory
+-------------
+
+A :class:`~google.cloud.spanner_v1.table.Table` object can be created with the
+:meth:`~google.cloud.spanner_v1.database.Database.table` factory method:
+
+.. code:: python
+
+    table = database.table("my_table_id")
+    if table.exists():
+        print("Table with ID 'my_table' exists.")
+    else:
+        print("Table with ID 'my_table' does not exist."
+
+
+Getting the Table Schema
+------------------------
+
+Use the :attr:`~google.cloud.spanner_v1.table.Table.schema` property to inspect
+the columns of a table as a list of
+:class:`~google.cloud.spanner_v1.types.StructType.Field` objects.
+
+.. code:: python
+
+    for field in table.schema
+        # `field` is a `Field` object.

google/cloud/spanner_v1/database.py

@@ -48,11 +48,12 @@
 )
 from google.cloud.spanner_admin_database_v1 import CreateDatabaseRequest
 from google.cloud.spanner_admin_database_v1 import UpdateDatabaseDdlRequest
-from google.cloud.spanner_v1 import ExecuteSqlRequest
 from google.cloud.spanner_v1 import (
+    ExecuteSqlRequest,
     TransactionSelector,
     TransactionOptions,
 )
+from google.cloud.spanner_v1.table import Table
 
 # pylint: enable=ungrouped-imports
 
@@ -68,6 +69,11 @@
 
 _DATABASE_METADATA_FILTER = "name:{0}/operations/"
 
+_LIST_TABLES_QUERY = """SELECT TABLE_NAME
+FROM INFORMATION_SCHEMA.TABLES
+WHERE SPANNER_STATE = 'COMMITTED'
+"""
+
 DEFAULT_RETRY_BACKOFF = Retry(initial=0.02, maximum=32, multiplier=1.3)
 
 
@@ -649,6 +655,41 @@ def list_database_operations(self, filter_="", page_size=None):
             filter_=database_filter, page_size=page_size
         )
 
+    def table(self, table_id):
+        """Factory to create a table object within this database.
+
+        Note: This method does not create a table in Cloud Spanner, but it can
+        be used to check if a table exists.
+
+        .. code-block:: python
+
+           my_table = database.table("my_table")
+           if my_table.exists():
+               print("Table with ID 'my_table' exists.")
+           else:
+               print("Table with ID 'my_table' does not exist.")
+
+        :type table_id: str
+        :param table_id: The ID of the table.
+
+        :rtype: :class:`~google.cloud.spanner_v1.table.Table`
+        :returns: a table owned by this database.
+        """
+        return Table(table_id, self)
+
+    def list_tables(self):
+        """List tables within the database.
+
+        :type: Iterable
+        :returns:
+            Iterable of :class:`~google.cloud.spanner_v1.table.Table`
+            resources within the current database.
+        """
+        with self.snapshot() as snapshot:
+            results = snapshot.execute_sql(_LIST_TABLES_QUERY)
+            for row in results:
+                yield self.table(row[0])
+
 
 class BatchCheckout(object):
     """Context manager for using a batch from a database.

google/cloud/spanner_v1/instance.py

@@ -361,7 +361,7 @@ def database(self, database_id, ddl_statements=(), pool=None, logger=None):
         """Factory to create a database within this instance.
 
         :type database_id: str
-        :param database_id: The ID of the instance.
+        :param database_id: The ID of the database.
 
         :type ddl_statements: list of string
         :param ddl_statements: (Optional) DDL statements, excluding the

google/cloud/spanner_v1/table.py

@@ -0,0 +1,126 @@
+# Copyright 2021 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""User friendly container for Cloud Spanner Table."""
+
+from google.cloud.exceptions import NotFound
+
+from google.cloud.spanner_v1.types import (
+    Type,
+    TypeCode,
+)
+
+
+_EXISTS_TEMPLATE = """
+SELECT EXISTS(
+    SELECT TABLE_NAME
+    FROM INFORMATION_SCHEMA.TABLES
+    WHERE TABLE_NAME = @table_id
+)
+"""
+_GET_SCHEMA_TEMPLATE = "SELECT * FROM {} LIMIT 0"
+
+
+class Table(object):
+    """Representation of a Cloud Spanner Table.
+
+    :type table_id: str
+    :param table_id: The ID of the table.
+
+    :type database: :class:`~google.cloud.spanner_v1.database.Database`
+    :param database: The database that owns the table.
+    """
+
+    def __init__(self, table_id, database):
+        self._table_id = table_id
+        self._database = database
+
+        # Calculated properties.
+        self._schema = None
+
+    @property
+    def table_id(self):
+        """The ID of the table used in SQL.
+
+        :rtype: str
+        :returns: The table ID.
+        """
+        return self._table_id
+
+    def exists(self):
+        """Test whether this table exists.
+
+        :rtype: bool
+        :returns: True if the table exists, else false.
+        """
+        with self._database.snapshot() as snapshot:
+            return self._exists(snapshot)
+
+    def _exists(self, snapshot):
+        """Query to check that the table exists.
+
+        :type snapshot: :class:`~google.cloud.spanner_v1.snapshot.Snapshot`
+        :param snapshot: snapshot to use for database queries
+
+        :rtype: bool
+        :returns: True if the table exists, else false.
+        """
+        results = snapshot.execute_sql(
+            _EXISTS_TEMPLATE,
+            params={"table_id": self.table_id},
+            param_types={"table_id": Type(code=TypeCode.STRING)},
+        )
+        return next(iter(results))[0]
+
+    @property
+    def schema(self):
+        """The schema of this table.
+
+        :rtype: list of :class:`~google.cloud.spanner_v1.types.StructType.Field`
+        :returns: The table schema.
+        """
+        if self._schema is None:
+            with self._database.snapshot() as snapshot:
+                self._schema = self._get_schema(snapshot)
+        return self._schema
+
+    def _get_schema(self, snapshot):
+        """Get the schema of this table.
+
+        :type snapshot: :class:`~google.cloud.spanner_v1.snapshot.Snapshot`
+        :param snapshot: snapshot to use for database queries
+
+        :rtype: list of :class:`~google.cloud.spanner_v1.types.StructType.Field`
+        :returns: The table schema.
+        """
+        query = _GET_SCHEMA_TEMPLATE.format(self.table_id)
+        results = snapshot.execute_sql(query)
+        # Start iterating to force the schema to download.
+        try:
+            next(iter(results))
+        except StopIteration:
+            pass
+        return list(results.fields)
+
+    def reload(self):
+        """Reload this table.
+
+        Refresh any configured schema into :attr:`schema`.
+
+        :raises NotFound: if the table does not exist
+        """
+        with self._database.snapshot() as snapshot:
+            if not self._exists(snapshot):
+                raise NotFound("table '{}' does not exist".format(self.table_id))
+            self._schema = self._get_schema(snapshot)

tests/system/test_system.py

@@ -42,6 +42,7 @@
 from google.cloud.spanner_v1 import KeySet
 from google.cloud.spanner_v1.instance import Backup
 from google.cloud.spanner_v1.instance import Instance
+from google.cloud.spanner_v1.table import Table
 
 from test_utils.retry import RetryErrors
 from test_utils.retry import RetryInstanceState
@@ -590,6 +591,65 @@ def _unit_of_work(transaction, name):
         self.assertEqual(len(rows), 2)
 
 
+class TestTableAPI(unittest.TestCase, _TestData):
+    DATABASE_NAME = "test_database" + unique_resource_id("_")
+
+    @classmethod
+    def setUpClass(cls):
+        pool = BurstyPool(labels={"testcase": "database_api"})
+        ddl_statements = EMULATOR_DDL_STATEMENTS if USE_EMULATOR else DDL_STATEMENTS
+        cls._db = Config.INSTANCE.database(
+            cls.DATABASE_NAME, ddl_statements=ddl_statements, pool=pool
+        )
+        operation = cls._db.create()
+        operation.result(30)  # raises on failure / timeout.
+
+    @classmethod
+    def tearDownClass(cls):
+        cls._db.drop()
+
+    def test_exists(self):
+        table = Table("all_types", self._db)
+        self.assertTrue(table.exists())
+
+    def test_exists_not_found(self):
+        table = Table("table_does_not_exist", self._db)
+        self.assertFalse(table.exists())
+
+    def test_list_tables(self):
+        tables = self._db.list_tables()
+        table_ids = set(table.table_id for table in tables)
+        self.assertIn("contacts", table_ids)
+        self.assertIn("contact_phones", table_ids)
+        self.assertIn("all_types", table_ids)
+
+    def test_list_tables_reload(self):
+        tables = self._db.list_tables()
+        for table in tables:
+            self.assertTrue(table.exists())
+            schema = table.schema
+            self.assertIsInstance(schema, list)
+
+    def test_reload_not_found(self):
+        table = Table("table_does_not_exist", self._db)
+        with self.assertRaises(exceptions.NotFound):
+            table.reload()
+
+    def test_schema(self):
+        table = Table("all_types", self._db)
+        schema = table.schema
+        names_and_types = set((field.name, field.type_.code) for field in schema)
+        self.assertIn(("pkey", TypeCode.INT64), names_and_types)
+        self.assertIn(("int_value", TypeCode.INT64), names_and_types)
+        self.assertIn(("int_array", TypeCode.ARRAY), names_and_types)
+        self.assertIn(("bool_value", TypeCode.BOOL), names_and_types)
+        self.assertIn(("bytes_value", TypeCode.BYTES), names_and_types)
+        self.assertIn(("date_value", TypeCode.DATE), names_and_types)
+        self.assertIn(("float_value", TypeCode.FLOAT64), names_and_types)
+        self.assertIn(("string_value", TypeCode.STRING), names_and_types)
+        self.assertIn(("timestamp_value", TypeCode.TIMESTAMP), names_and_types)
+
+
 @unittest.skipIf(USE_EMULATOR, "Skipping backup tests")
 @unittest.skipIf(SKIP_BACKUP_TESTS, "Skipping backup tests")
 class TestBackupAPI(unittest.TestCase, _TestData):

tests/unit/test_database.py

@@ -1293,6 +1293,26 @@ def test_list_database_operations_explicit_filter(self):
             filter_=expected_filter_, page_size=page_size
         )
 
+    def test_table_factory_defaults(self):
+        from google.cloud.spanner_v1.table import Table
+
+        client = _Client()
+        instance = _Instance(self.INSTANCE_NAME, client=client)
+        pool = _Pool()
+        database = self._make_one(self.DATABASE_ID, instance, pool=pool)
+        my_table = database.table("my_table")
+        self.assertIsInstance(my_table, Table)
+        self.assertIs(my_table._database, database)
+        self.assertEqual(my_table.table_id, "my_table")
+
+    def test_list_tables(self):
+        client = _Client()
+        instance = _Instance(self.INSTANCE_NAME, client=client)
+        pool = _Pool()
+        database = self._make_one(self.DATABASE_ID, instance, pool=pool)
+        tables = database.list_tables()
+        self.assertIsNotNone(tables)
+
 
 class TestBatchCheckout(_BaseTest):
     def _get_target_class(self):