不同的实体框架 [英] Distinct in Entity framework

问题描述

我有一些人有相同的标识对象的名单，所以我想删除被复制的那些元素。

I have a List of objects that some of them have the same Ids, so I would like to remove those elements that are duplicated.

我试着用是这样的：

List<post> posts = postsFromDatabase.Distinct().ToList();

不过，这是行不通的！

But it doesn't work!

所以，我为了避免重复写了这个方法：

So I wrote this method in order to avoid the duplicates:

public List<Post> PostWithOutDuplicates(List<Post> posts)
    {
        List<Post> postWithOutInclude = new List<Post>();
        var noDupes = posts.Select(x => x.Id).Distinct();
        if (noDupes.Count() < posts.Count)
        {
            foreach (int idPost in noDupes)
            {
                postWithOutInclude.Add(posts.Where(x => x.Id == idPost).First());
            }
            return postWithOutInclude;
        }
        else
        {
            return posts;
        }
    }

如何提高性能？​​任何想法

Any ideas of how to improve the performance??

感谢名单提前。

推荐答案

这是很好的和容易：

List<Post> posts = posts
.GroupBy(x => x.Id)
.Select(x => x.FirstOrDefault())

但是，如果你想要写的正确方法，我建议你把它写这样的：

But if you want to write it the proper way, I'd advise you to write it like this:

public class PostComparer : IEqualityComparer<Post>
{
    #region IEqualityComparer<Post> Members

    public bool Equals(Post x, Post y)
    {
        return x.Id.Equals(y.Id);
    }

    public int GetHashCode(Post obj)
    {
        return obj.Id.GetHashCode();
    }

    #endregion
}

由于它会给你更多的自由，当它涉及到更多的比较。写过这个类，你可以使用它是这样的：

As it will give you more freedom when it comes to additional comparisons. having written this class you can use it like this:

List<Post> posts = postsFromDatabase.Distinct(new PostComparer()).ToList();

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