是否可以在 EntityFramework 中将 Select(l=> new{}) 与 SelectMany 一起使用

发布于 2024-08-02 23:46:19 字数 1103 浏览 1 评论 0原文

我正在尝试一些我不太确定的事情，但我想在这里问是否可能。

能做到吗？

public IQueryable<Info> GetInfo(int count, byte languageId)
        {
            return db.Info.SelectMany(i => i.LanguageInfo)
                              .Where(l => l.Language.id == languageId)
                              .Select(l => new Info {   AddDate = l.Info.AddDate,
                                                        Description = l.Description,
                                                        EntityKey = l.Info.EntityKey,
                                                        id = l.Info.id,
                                                        Title = l.Title,
                                                        ViewCount = l.Info.ViewCount }
                                                        )
                              .OrderByDescending(i => i.id)
                              .Take(count);
        }

当执行这个方法时我得到一个错误

实体或复杂类型 “GuideModel.Info”不能在 LINQ to Entities 中构建查询。

是“不可能”的意思吗？

谢谢

原文

I am trying something that i not really sure but i want to ask here if it s possible.

Is it able to be done ?

public IQueryable<Info> GetInfo(int count, byte languageId)
        {
            return db.Info.SelectMany(i => i.LanguageInfo)
                              .Where(l => l.Language.id == languageId)
                              .Select(l => new Info {   AddDate = l.Info.AddDate,
                                                        Description = l.Description,
                                                        EntityKey = l.Info.EntityKey,
                                                        id = l.Info.id,
                                                        Title = l.Title,
                                                        ViewCount = l.Info.ViewCount }
                                                        )
                              .OrderByDescending(i => i.id)
                              .Take(count);
        }

When this method is executed i got an error

The entity or complex type
'GuideModel.Info' cannot be
constructed in a LINQ to Entities
query.

Does it mean "not possible" ?

Thank you

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土豪 2024-08-09 23:46:19

该错误本质上表明实体框架不知道如何创建 Info 对象，因为它未绑定到表对象。（换句话说，IQueryable 上的 Select 调用无法转换为等效的 SQL。）您可以通过以下方式在客户端上执行 Select 投影： :

public IQueryable<Info> GetInfo(int count, byte languageId)
{
    return db.Info.SelectMany(i => i.LanguageInfo)
                      .Where(l => l.Language.id == languageId)
                      .Take(count)
                      .AsEnumerable()
                      .Select(l => new Info {   AddDate = l.Info.AddDate,
                                                Description = l.Description,
                                                EntityKey = l.Info.EntityKey,
                                                id = l.Info.id,
                                                Title = l.Title,
                                                ViewCount = l.Info.ViewCount }
                                                )
                      .OrderByDescending(i => i.id);
}

The error essentially indicates that the Entity Framework doesn't know how to create an Info object, since it is not bound to a table object. (Put another way, the Select call on the IQueryable cannot be translated into equivalent SQL.) You could perform the Select projection on the client via:

public IQueryable<Info> GetInfo(int count, byte languageId)
{
    return db.Info.SelectMany(i => i.LanguageInfo)
                      .Where(l => l.Language.id == languageId)
                      .Take(count)
                      .AsEnumerable()
                      .Select(l => new Info {   AddDate = l.Info.AddDate,
                                                Description = l.Description,
                                                EntityKey = l.Info.EntityKey,
                                                id = l.Info.id,
                                                Title = l.Title,
                                                ViewCount = l.Info.ViewCount }
                                                )
                      .OrderByDescending(i => i.id);
}

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烙印 2024-08-09 23:46:19

可以使用Select(l => new ...)，但不能与实体类型一起使用。您需要使用匿名类型或带有无参数构造函数的 POCO 类型。实体类型因其与 ObjectContext 交互的方式而显得“特殊”。您可以选择它们，但不能在查询中新建它们。

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左岸枫 2024-08-09 23:46:19

下面的代码对我有用。这里的“SearchTerm”是一个复杂类型。谢谢杰森:)

var lstSynonym = TechContext.TermSynonyms
                .Where(p => p.Name.StartsWith(startLetter))
                .AsEnumerable()
                .Select(u => new SearchTerm
                                 {
                                     ContentId = u.ContentId,
                                     Title = u.Name,
                                     Url = u.Url
                                 });

The code below worked for me. Here "SearchTerm" is a complex type. Thanks Jason :)

var lstSynonym = TechContext.TermSynonyms
                .Where(p => p.Name.StartsWith(startLetter))
                .AsEnumerable()
                .Select(u => new SearchTerm
                                 {
                                     ContentId = u.ContentId,
                                     Title = u.Name,
                                     Url = u.Url
                                 });

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