删除重复项，而在LINQ合并使用联盟列表 [英] Remove duplicates while merging lists using Union in LINQ

问题描述

我想在 LinqPad 合并使用 list.Union 两份名单，但我不能得到它。工作和想检查我的理解是正确的。

I am trying to merge two lists using list.Union in LinqPad but I can't get it to work and wanted to check my understanding is correct.

鉴于这种简单的类：

public class Test 
{
   public int Id { get; set;}
   public int field1 { get; set; }

   public bool Equals(Test other)
   {        
      return this.Id.Equals(other.Id);
   }
}

和两个列表填充是这样的：

And two lists populated like this:

List<Test> list = new List<Test>();
list.Add( new Test { Id = 1, field1 = 1});
list.Add( new Test { Id = 1, field1 = 2});
list.Add( new Test { Id = 2, field1 = 3});
list.Add( new Test { Id = 2, field1 = 4});

List<Test> list2 = new List<Test>();
list2.Add( new Test { Id = 1, field1 = 1});
list2.Add( new Test { Id = 1, field1 = 2});
list2.Add( new Test { Id = 2, field1 = 3});
list2.Add( new Test { Id = 2, field1 = 4});

我再尝试： VAR mergedList = list.Union（列表2）.ToList （）; 和输出使用一个简单的的foreach 循环中的数据，并得到如下的输出：

I then try: var mergedList = list.Union(list2).ToList(); and output the data using a simple foreach loop and get this output:

ID: 1 -------- 1
ID: 1 -------- 2
ID: 2 -------- 3
ID: 2 -------- 4
ID: 1 -------- 1
ID: 1 -------- 2
ID: 2 -------- 3
ID: 2 -------- 4

我的印象是，联盟应删除重复的返回：

I was under the impression that Union should remove the duplicates to return:

ID: 1 -------- 1
ID: 1 -------- 2
ID: 2 -------- 3
ID: 2 -------- 4

我是不是做错了什么或曾经我误解了？

Am I doing something wrong or have I misunderstood?

此外，如果它没有明确覆盖等于方法在测试类？

Also, should it work without explicitly overriding the Equals method in the Test class?

感谢

推荐答案

在你的情况，你只需定义一些方法，即LINQ一无所知。这就像创建方法布尔HeyEquateMeWith（测试等）和期望，这样做设置操作时，LINQ将调用它。

In your case you simply define some method, that LINQ knows nothing about. It's like creating method bool HeyEquateMeWith(Test other) and expect, that LINQ will call it when doing set operations.

您需要定义类如下（替换 对象的等于和的GetHashCode 方法）：

You need to define your class as following (override Object's Equals and GetHashCode methods):

public class Test 
{
   public int Id { get; set;}
   public int field1 { get; set; }  

   public override bool Equals(object other) //note parameter is of type object
   {        
        Test t = other as Test;
        return (t != null) ? Id.Equals(t.Id) : false;
   }

   public override int GetHashCode()
   {
        return Id.GetHashCode();
   }
}

现在联盟将调用您的重写等于和的GetHashCode 方法。你也应该 的ALWAYS覆盖的GetHashCode 在覆盖等于方法。

Now Union will call your overridden Equals and GetHashCode methods. Also you should ALWAYS override GetHashCode when you override Equals method.

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