LINQ to Entities无法识别方法'System.String ToString(Int32)' [英] LINQ to Entities does not recognize the method 'System.String ToString(Int32)'

问题描述

我正在使用linq查询，该查询将LINQ抛出错误到实体，但无法识别方法'System.String ToString(Int32)'，因此无法将该方法转换为商店表达式.

Hi I am using a linq query which is throwing the error LINQ to Entities does not recognize the method 'System.String ToString(Int32)' method, and this method cannot be translated into a store expression.

        List<string> resultMap = (from item in mapResult
                                  select Convert.ToString(item.ResultDE)).ToList();

下面的语句中引发错误

        List<Result_DE> resultList = (from result in db.Result_DE
                                      where result.IsActive == "1"
                                      && resultMap.Contains(Convert.ToString(Convert.ToInt32(result.ID)))
                                      select result).ToList();

请告诉我编写此查询的正确方法.

please tell me the proper way of writing this query.

推荐答案

您不能在LINQ to Entities语句中使用这些转换函数，它们无法转换为SQL，您需要在内存中进行转换.但我认为您根本不需要这样做.

You cannot use these conversion functions in a LINQ to Entities statement, they cannot be translated to SQL, you need to do the conversions in memory. But I don't think you need to do that at all.

如果您只是使用resultMap来获取resultList，并按Results进行过滤，而Id存在于mapResult中，请执行以下操作:

If you were just using the resultMap to get your resultList, filtered by Results of which the Id is present in mapResult, do the following:

var resultList = db.Result_DE
    .Where(r => r.IsActive == "1" && mapResult.Any(mr => mr.ResultDE == r.ID));
    .ToList();

如果mapResult是内存中的集合，而不是附加到db上下文的IQueryable，则需要执行以下操作:

If mapResult is an in-memory collection, instead of an IQueryable that is attached to the db context, you need to do the following:

var resultIds = mapResult.Select(mr => mr.ResultDE).ToList();
var resultList = db.Result_DE
    .Where(r => r.IsActive == "1" && resultIds.Contains(r.ID));
    .ToList();

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