DropColumn有条件地在迁移中

我的列上还存在一个默认约束，因此得到以下结果：

public override void Up(){    Sql(@"IF EXISTS(     SELECt 1 FROM sys.columns c     INNER JOIN sys.tables t ON t.object_id = c.object_id     WHERe c.name = 'AttributeId' AND t.name = 'MyObjects')     BEGIN       DECLARE @AttributeIdDefConstraint nvarchar(128)       SELECt @AttributeIdDefConstraint = name       FROM sys.default_constraints       WHERe parent_object_id = object_id(N'dbo.MyObjects')         AND col_name(parent_object_id, parent_column_id) = 'AttributeId';       IF @AttributeIdDefConstraint IS NOT NULL       BEGIN     EXECUTE('ALTER TABLE [dbo].[MyObjects] DROP ConSTRAINT ' + @AttributeIdDefConstraint)       END       ALTER TABLE [dbo].[MyObjects] DROP COLUMN [AttributeId]     END");}

希望可以节省时间。