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方法无法转换为存储表达式

repository-pattern linq-to-entities entity-framework c#

Shawn Mclean · 技术社区 · 16 年前

我看到这段代码与LINQ to SQL一起工作,但当我使用实体框架时,它抛出以下错误:

LINQ to Entities不识别该方法的系统Linq IQueryable'1[MyProject.Models.CommunityFeatures项目]GetCommunityFeatures()'方法,并且此方法无法转换为存储表达式`

存储库代码如下:

public IQueryable<Models.Estate> GetEstates()
{
    return from e in entity.Estates
           let AllCommFeat = GetCommunityFeatures()
           let AllHomeFeat = GetHomeFeatures()
           select new Models.Estate
                      {
                                EstateId = e.EstateId,
                                AllHomeFeatures = new LazyList<HomeFeatures>(AllHomeFeat),
                                AllCommunityFeatures = new LazyList<CommunityFeatures>(AllCommFeat)
                      };
}

public IQueryable<Models.CommunityFeatures> GetCommunityFeatures()
{
    return from f in entity.CommunityFeatures
           select new CommunityFeatures
                      {
                          Name = f.CommunityFeature1,
                          CommunityFeatureId = f.CommunityFeatureId
                      };
}

public IQueryable<Models.HomeFeatures> GetHomeFeatures()
{
    return from f in entity.HomeFeatures
           select new HomeFeatures()
           {
               Name = f.HomeFeature1,
               HomeFeatureId = f.HomeFeatureId
           };
}

LazyList是一个扩展IQueryable功能的列表。

1 回复 | 直到 13 年前

116

Marcus Mangelsdorf user1542042 11 年前

原因: 根据设计, LINQ to Entities
更具体地说,linqto实体只支持 无参数构造函数 和 初始值设定项 .

解决方案: 因此,为了克服这个异常,需要将子查询合并到主查询中和 GetHomeFeatures() 而不是直接从LINQ查询中调用方法。另外,在您试图实例化的新实例的行上也有一个问题懒鬼使用它的参数化构造函数,就像您在 解决并发冲突 . 为此,解决方案是切换到LINQ查询的客户机评估(LINQ到对象)。这将要求您调用 AsEnumerable 在调用LazyList构造函数之前,用于LINQ to Entities查询的方法。

public IQueryable<Models.Estate> GetEstates()
{
    return from e in entity.Estates.AsEnumerable()
       let AllCommFeat = from f in entity.CommunityFeatures
                         select new CommunityFeatures {
                             Name = f.CommunityFeature1,
                             CommunityFeatureId = f.CommunityFeatureId
                         },
       let AllHomeFeat = from f in entity.HomeFeatures
                         select new HomeFeatures() {
                             Name = f.HomeFeature1,
                             HomeFeatureId = f.HomeFeatureId
                         },
       select new Models.Estate {
            EstateId = e.EstateId,
            AllHomeFeatures = new LazyList<HomeFeatures>(AllHomeFeat),
            AllCommunityFeatures = new LazyList<CommunityFeatures>(AllCommFeat)
       };
}

更多信息: 请看一看 LINQ to Entities, what is not supported? 更多信息。 LINQ to Entities, Workarounds on what is not supported 详细讨论可能的解决方案。 (两个链接都是缓存版本,因为原始网站已关闭)