实体框架3.0包含无法像在EF Core 2.2中那样在SQL中进行翻译

问题描述

我正在尝试将Web API从.NET Core 2.2迁移到.NET Core 3.0，但偶然发现以下内容:

I am trying to migrate a Web API from .NET Core 2.2 to .NET Core 3.0 and I have stumbled across the following:

public Dictionary<int, Tag> GetTagMap(IList<int> tagIds = null)
{
    var tags = context.Tag.AsNoTracking();
    if (tagIds != null)
        tags = tags.Where(t => tagIds.Contains(t.TagId));

    return tags
       .ToList()       // explicit client evaluation in 3.0
       .ToDictionary(t => t.TagId, t => t);
}

这通常会生成类似于以下内容的SQL语句:

This used to generate a SQL statement similar to this one:

SELECT TagId, Name FROM Tag WHERE TagId IN (1, 2, 3)

对于正确索引的列和少量的IN值非常有用.

which worked very well for correctly indexed column and a small number of IN values.

现在，我收到以下错误消息，提示不再支持List<>.Contains翻译:

Now I receive the following error suggesting that List<>.Contains translation is not supported anymore:

这表明不再在客户端上评估LINQ查询重大更改，但未在客户端上评估AFAIK Contains.

This suggests the LINQ queries are no longer evaluated on the client breaking change, but AFAIK Contains was not evaluated on the client.

推荐答案

这是一个3.0错误，由#17342:包含在通用IList/HashSet/ImmutableHashSet上将引发异常.

It's a 3.0 bug, tracked by #17342: Contains on generic IList/HashSet/ImmutableHashSet will throw exception.

已在3.1中修复.解决方法(如果您迫不及待)是例如强制使用Enumerable.Contains

Already fixed in 3.1. The workaround (if you can't wait) is to force the usage of Enumerable.Contains, for instance

t => tagIds.AsEnumerable().Contains(t.TagId)

或更改变量的类型.

这篇关于实体框架3.0包含无法像在EF Core 2.2中那样在SQL中进行翻译的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！