NotSupportedException:实体的LINQ无法识别该方法 [英] NotSupportedException: LINQ to Entities does not recognize the method

问题描述

我正在尝试使此查询与EF一起使用，但会引发异常:

I'm trying to make this query work with EF but it throws an exception:

var c = ac.Communities.OrderBy(o => o.Posts.Count())
        .Skip(page*limit)
        .Take(limit)
        .Select(o => o.ToViewModel()).ToArray();

Community模型中的ToViewModel()方法如下所示:

The ToViewModel() method from the Community model looks like this:

public CommunityModel ToViewModel()
{
    return new CommunityModel()
    {
        category = Category.Name,
        created = CreationTime,
        description = Description,
        id = Id,
        name = Name,
        ownerId = Owner.Id,
        postsCount = Posts.Count(),
        score = Posts.Sum(o => o.Likes - o.Unlikes),
        shortDescription = ShortDescription,
        subscribersCount = Subscribers.Count(),
    };
}

我在做什么错了?

推荐答案

Entity Framework无法转换您在ToViewModel内部使用的方法.使用ToList()急于加载结果，然后映射它们，从而避免了EF尝试翻译SQL的需要:

Entity Framework cannot translate the methods you are using inside ToViewModel. Use ToList() to eagerly load the results, then map those instead, avoiding the need for EF to try to translate the SQL:

var c = ac.Communities.OrderBy(o => o.Posts.Count())
    .Skip(page*limit)
    .Take(limit)
    .ToList()
    .Select(o => o.ToViewModel()).ToArray();

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