使用 LINQ 连接三个表

Question

如何加入三个表并获得所有值 对于两个表我参考

using(Dataclasscontext DbContext = new Dataclasscontext())
{
   var result = (from t1 in DbContext.tbl1 join t2 in DbContext.tbl2 on t1.id equel t2.id select new {t1.id,t1.name,t2.class,t2.std}).toArray();
}

我参考了三个表

using(Dataclasscontext DbContext = new Dataclasscontext())
{
   var result = (from t1 in DbContext.tbl1 
                 from t2 in DbContext.tbl2 where t1.id1 == t2.id1 
                 from t3 in Db`enter code here`Context.tbl3 where t2.id2 == t3.id2).toArray();
}

但不希望这种类型的查询用于连接三个表。有没有人帮我用 join 加入三个表

Answer 1

我不是 100% 确定你想做什么，但我认为你想摆脱“来自”。

这是一个仅使用带有“经典方法”的 Linq 的示例：

// Testclasses which will be joined
public class TestClass1
{
    public int Id { get; set; }
    public string Name1 { get; set; }
}
public class TestClass2
{
    public int Id { get; set; }
    public string Name2 { get; set; }
}

static void Main()
{
    // define some example-data
    List<TestClass1> list1 = new List<TestClass1>()
    {
        new TestClass1() { Id = 1, Name1 = "One1" },
        new TestClass1() { Id = 2, Name1 = "Two1" },
        new TestClass1() { Id = 3, Name1 = "Three1" }
    };
    List<TestClass2> list2 = new List<TestClass2>()
    {
        new TestClass2() { Id = 1, Name2 = "One2" },
        new TestClass2() { Id = 2, Name2 = "Two2" },
        new TestClass2() { Id = 3, Name2 = "Three2" }
    };

    // Here the 'magic' happens:
    // We perform a join one our 1st list
    // We send list2 as list to join with
    // We define two key-selectors in lambda-expressions: t1 => t1.Id and t2 => t2.Id
    // We form the joined object as anonymous type: (t1, t2) => new { Id = t1.Id, Name1 = t1.Name1, Name2 = t2.Name2}
    var joinedList = list1.Join(
        list2,
        t1 => t1.Id,
        t2 => t2.Id,
        (t1, t2) => new { Id = t1.Id, Name1 = t1.Name1, Name2 = t2.Name2 }
        );

    foreach (var item in joinedList)
    {
        Console.WriteLine("Id: {0}, Name1: {1}, Name2: {2}", item.Id, item.Name1, item.Name2);
    }
}