如何在LINQ中"INSERT INTO table1(...)SELECT(...)FROM table2"？

Question

如何编写LINQ to SQL等效于:

INSERT INTO Table1 (field1, field2, field3)
SELECT field1, field2, field3
FROM Table2
WHERE (field1= @field1)

谢谢

Answer 1

由于您没有返回任何结果,只需使用低级DataContext.ExecuteCommand()方法:

using (MyDataContext dc = new MyDataContext())
{
    dc.ExecuteCommand(@"
        INSERT INTO Table1 (field1, field2, field3)
        SELECT field1, field2, field3
        FROM Table2
        WHERE (field1= {0})
        ",
        field1);
}

Answer 2

LINQ 是一种查询语言，因此它不执行更新或插入操作。然而，LINQ to SQL 实体对象模型具有处理 CUD 的方法：

using(MyDataContext dc = new MyDataContext())
{
    //select the source entities from Table2
    var Table2Entities = (from e in dc.Table2 where e.Field1 == "value" select e);

    //for each result, create a new Table1 entity and attach to Table1
    Table2Entities.ForEach(t2e => dc.Table1.InsertOnSubmit(
        new Table1Entity {
            Field1 = t2e.Field1,
            Field2 = t2e.Field2,
            Field3 = t2e.Field3
        });

    //submit the changes
    dc.SubmitChanges();
}

这里真正的区别在于它需要两个单独的 SQL 事务，而不是一个 - 一个用于选择，一个用于插入。