add support for snapshot_read_only transactions

Author: Valeriya Popova

CHANGELOG.md

@@ -1,3 +1,5 @@
+* add `SnapshotReadOnly` transaction mode support to `session.transaction`
+
 ## 2.11.1 ##
 * Regenerate protobuf code from public api protos (some private protobufs was removed)
 * Remove internal S3 client code

tests/aio/test_tx.py

@@ -49,3 +49,45 @@ async def test_credentials():
         raised = True
 
     assert raised
+
+
+@pytest.mark.asyncio
+async def test_tx_snapshot_ro(driver, database):
+    session = await driver.table_client.session().create()
+    description = (
+        ydb.TableDescription()
+        .with_primary_keys("key")
+        .with_columns(
+            ydb.Column("key", ydb.OptionalType(ydb.PrimitiveType.Uint64)),
+            ydb.Column("value", ydb.OptionalType(ydb.PrimitiveType.Uint64)),
+        )
+    )
+    await session.create_table(database + "/test", description)
+    await session.transaction(ydb.SerializableReadWrite()).execute(
+        """INSERT INTO `test` (`key`, `value`) VALUES (1, 1), (2, 2)""",
+        commit_tx=True,
+    )
+
+    ro_tx = session.transaction(tx_mode=ydb.SnapshotReadOnly())
+    data1 = await ro_tx.execute("SELECT value FROM `test` WHERE key = 1")
+
+    rw_tx = session.transaction(ydb.SerializableReadWrite())
+    await rw_tx.execute("UPDATE `test` SET value = value + 1")
+    data2 = await ro_tx.execute("SELECT value FROM `test` WHERE key = 1")
+
+    await rw_tx.commit()
+    data3 = await ro_tx.execute("SELECT value FROM `test` WHERE key = 1")
+
+    assert data1[0].rows == data2[0].rows == data3[0].rows == [{"value": 1}]
+
+    await ro_tx.commit()
+
+    with pytest.raises(ydb.issues.GenericError) as exc_info:
+        await ro_tx.execute("UPDATE `test` SET value = value + 1")
+    assert "read only transaction" in exc_info.value.message
+
+    data = await session.transaction(tx_mode=ydb.SnapshotReadOnly()).execute(
+        "SELECT value FROM `test` WHERE key = 1",
+        commit_tx=True,
+    )
+    assert data[0].rows == [{"value": 2}]

ydb/table.py

@@ -780,6 +780,22 @@ def settings(self):
         pass
 
 
+class SnapshotReadOnly(AbstractTransactionModeBuilder):
+    __slots__ = ("_pb", "_name")
+
+    def __init__(self):
+        self._pb = _apis.ydb_table.SnapshotModeSettings()
+        self._name = "snapshot_read_only"
+
+    @property
+    def settings(self):
+        return self._pb
+
+    @property
+    def name(self):
+        return self._name
+
+
 class SerializableReadWrite(AbstractTransactionModeBuilder):
     __slots__ = ("_pb", "_name")