Remove unused DeleteFromSelect db api method

Noticed this while I was working on archive_deleted_rows when the code
comment didn't appear to be true and was confusing.

Change I4f2e1632aac96afa7ce06908dc30c0716bcb87b2 removed the last usage
of the DeleteFromSelect method, so remove the unused code to avoid
future confusion.

Change-Id: I4c7574898b64c8f8172ddc84ced86b8a70bf39ff

Author: melwitt

nova/db/sqlalchemy/api.py

@@ -38,7 +38,6 @@
 from sqlalchemy import and_
 from sqlalchemy import Boolean
 from sqlalchemy.exc import NoSuchTableError
-from sqlalchemy.ext.compiler import compiles
 from sqlalchemy import Integer
 from sqlalchemy import MetaData
 from sqlalchemy import or_
@@ -52,7 +51,6 @@
 from sqlalchemy.sql.expression import asc
 from sqlalchemy.sql.expression import cast
 from sqlalchemy.sql.expression import desc
-from sqlalchemy.sql.expression import UpdateBase
 from sqlalchemy.sql import false
 from sqlalchemy.sql import func
 from sqlalchemy.sql import null
@@ -367,23 +365,6 @@ def clauses(self, field):
         return [field != value for value in self.values]
 
 
-class DeleteFromSelect(UpdateBase):
-    def __init__(self, table, select, column):
-        self.table = table
-        self.select = select
-        self.column = column
-
-
-# NOTE(guochbo): some versions of MySQL doesn't yet support subquery with
-# 'LIMIT & IN/ALL/ANY/SOME' We need work around this with nesting select .
-@compiles(DeleteFromSelect)
-def visit_delete_from_select(element, compiler, **kw):
-    return "DELETE FROM %s WHERE %s in (SELECT T1.%s FROM (%s) as T1)" % (
-        compiler.process(element.table, asfrom=True),
-        compiler.process(element.column),
-        element.column.name,
-        compiler.process(element.select))
-
 ###################
 
 
@@ -4202,8 +4183,7 @@ def _archive_deleted_rows_for_table(metadata, tablename, max_rows, before):
         column = table.c.domain
     else:
         column = table.c.id
-    # NOTE(guochbo): Use DeleteFromSelect to avoid
-    # database's limit of maximum parameter in one SQL statement.
+
     deleted_column = table.c.deleted
     columns = [c.name for c in table.c]
 

nova/tests/unit/db/test_migration_utils.py

@@ -16,11 +16,9 @@
 from oslo_db.sqlalchemy import enginefacade
 from oslo_db.sqlalchemy import test_base
 from oslo_db.sqlalchemy import test_fixtures
-from oslo_utils import uuidutils
 from sqlalchemy import Integer, String
 from sqlalchemy import MetaData, Table, Column
 from sqlalchemy.exc import NoSuchTableError
-from sqlalchemy import sql
 from sqlalchemy.types import UserDefinedType
 
 from nova.db.sqlalchemy import api as db
@@ -57,39 +55,6 @@ def setUp(self):
         self.engine = enginefacade.writer.get_engine()
         self.meta = MetaData(bind=self.engine)
 
-    def test_delete_from_select(self):
-        table_name = "__test_deletefromselect_table__"
-        uuidstrs = []
-        for unused in range(10):
-            uuidstrs.append(uuidutils.generate_uuid(dashed=False))
-
-        conn = self.engine.connect()
-        test_table = Table(table_name, self.meta,
-                           Column('id', Integer, primary_key=True,
-                                  nullable=False, autoincrement=True),
-                           Column('uuid', String(36), nullable=False))
-        test_table.create()
-        # Add 10 rows to table
-        for uuidstr in uuidstrs:
-            ins_stmt = test_table.insert().values(uuid=uuidstr)
-            conn.execute(ins_stmt)
-
-        # Delete 4 rows in one chunk
-        column = test_table.c.id
-        query_delete = sql.select([column],
-                                  test_table.c.id < 5).order_by(column)
-        delete_statement = db.DeleteFromSelect(test_table,
-                                               query_delete, column)
-        result_delete = conn.execute(delete_statement)
-        # Verify we delete 4 rows
-        self.assertEqual(result_delete.rowcount, 4)
-
-        query_all = sql.select([test_table])\
-                       .where(test_table.c.uuid.in_(uuidstrs))
-        rows = conn.execute(query_all).fetchall()
-        # Verify we still have 6 rows in table
-        self.assertEqual(len(rows), 6)
-
     def test_check_shadow_table(self):
         table_name = 'test_check_shadow_table'