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 [英] Entity Framework 3.0 Contains cannot be translated in SQL as it was in EF Core 2.2

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:

System.InvalidOperationException:'LINQ表达式'Where( 来源:DbSet，谓词:(t)=>(未处理的参数: __tagIds_0).包含(t.TagId))'无法翻译.以可以翻译的形式重写查询，或切换到 通过插入对其中任何一个的调用来显式地进行客户评估 AsEnumerable()，AsAsyncEnumerable()，ToList()或ToListAsync().看 客户端与服务器评估-EF核心，以获取更多信息.'

System.InvalidOperationException: 'The LINQ expression 'Where( source: DbSet, predicate: (t) => (Unhandled parameter: __tagIds_0).Contains(t.TagId))' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync(). See Client vs. Server Evaluation - EF Core for more information.'

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.

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