嵌套LINQ返回这种方法不能被翻译成店表情异常 [英] Nested LINQ returning a this method cannot be translated into a store expression exception

问题描述

下面的LINQ：

retval = ( from jm in entities.JobMasters
                 where jm.UserId == userId && jm.IsRemote == false
                 select new JobDto
                 {
                     JobMasterId = jm.JobMasterId,
                     ExternalTaskId = jm.ExternalTaskId,
                     JobDetails = ( from jd in entities.JobDetails
                                    where jd.JobMasterId == jm.JobMasterId
                                    select new JobDetailDto { ScreenFieldId = jd.ScreenFieldId, FieldValue = jd.FieldValue }
                     ).ToList()
                 }
            ).ToList();

是给我这个错误：

is giving me this error:

LINQ实体无法识别方法
位System.Collections.Generic.List`1 [KernWcfTest.DataTransferObjects.JobDetailDto]
了ToList [JobDetailDto]（System.Collections.Generic .IEnumerable`1 [KernWcfTest.DataTransferObjects.JobDetailDto]）'方法，
和这种方法不能被翻译成商店表达

LINQ to Entities does not recognize the method 'System.Collections.Generic.List`1[KernWcfTest.DataTransferObjects.JobDetailDto] ToList[JobDetailDto](System.Collections.Generic.IEnumerable`1[KernWcfTest.DataTransferObjects.JobDetailDto])' method, and this method cannot be translated into a store expression.

下面是两个DTO类：

[DataContract]
public class JobDetailDto
{
    [DataMember]
    public int ScreenFieldId { get; set; }

    [DataMember]
    public string FieldValue { get; set; }
}

[DataContract]
[KnownType(typeof(JobDetailDto))]
public class JobDto
{
    [DataMember]
    public int JobMasterId { get; set; }

    [DataMember]
    public string ExternalTaskId { get; set; }

    [DataMember]
    public List<JobDetailDto> JobDetails { get; set; }
}

问题是子选择和JobDetails列表。我尝试添加了KnownType，但没有奏效。

The problem is the sub-select and the JobDetails list. I tried adding the KnownType but it didn't work.

这所有的作品在LINQ垫罚款。

This all works fine in LINQ Pad.

任何想法？

干杯

史蒂夫

推荐答案

别ŧ调用了ToList的内部查询（一个为JobDetails）。错误是这你所说的.ToList方法 - 它不能被转换为T-SQL！

Don't call ToList on the inner query (the one for JobDetails). The error is "This .ToList method you speak of -- it can't be translated to T-SQL!"

这应该工作：

retval = ( from jm in entities.JobMasters
             where jm.UserId == userId && jm.IsRemote == false
             select new JobDto
             {
                 JobMasterId = jm.JobMasterId,
                 ExternalTaskId = jm.ExternalTaskId,
                 JobDetails =   from jd in entities.JobDetails
                                where jd.JobMasterId == jm.JobMasterId
                                select new JobDetailDto { ScreenFieldId = jd.ScreenFieldId, FieldValue = jd.FieldValue }
                 )
             }
        ).ToList();

请注意，您可以调用了ToList在查询的结尾，因为这部分并不需要转换为T-SQL。

Note that you can call ToList on the end of the query, as that part doesn't need to be translated to T-SQL.

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