实体框架Lambda谓词存储在var与关联 | 实体框架Lambda谓词存储在var与关联

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问题描述

我有一个使用EF6的通用存储库。该问题与需要包含的关联属性有关，即使它不应该。以下作品：

  IQueryable< User> dbQuery = _db.Set< User>（）; 
 return dbQuery.Where（x => x.Child.Name ==Foo）。ToList（）;

但是，以下内容不起作用：

  Func< User，bool> filter = x => x.Child.Name ==Foo; 
 IQueryable< User> dbQuery = _db.Set< User>（）; 
 return dbQuery.Where（filter）.ToList（）;

它在Child上引发Object Reference not set ...异常。

以下解决方法：

  Func< User，bool> filter = x => x.Child.Name ==Foo; 
 IQueryable< User> dbQuery = _db.Set< User>（）; 
 dbQuery = dbQuery.Include（x => x.Child）; 
 return dbQuery.Where（filter）.ToList（）;

我不明白为什么这是必要的。任何人都知道如何解决这个问题，而不使用Include？

解决方案

你应该使用表达式让EF提供商解析您的查询。

将 Func< User，bool> 更改为 Expression&FunC< User，bool& ;>

I have a generic repository using EF6. The issue has to do with association properties requiring an "Include" even though it shouldn't. The following works:

IQueryable<User> dbQuery = _db.Set<User>();
return dbQuery.Where(x => x.Child.Name == "Foo").ToList();

However, the following does not work:

Func<User, bool> filter = x => x.Child.Name == "Foo";
IQueryable<User> dbQuery = _db.Set<User>();
return dbQuery.Where(filter).ToList();

It throws an "Object Reference not set..." exception on Child.

The following resolves it:

Func<User, bool> filter = x => x.Child.Name == "Foo";
IQueryable<User> dbQuery = _db.Set<User>();
dbQuery = dbQuery.Include(x => x.Child);
return dbQuery.Where(filter).ToList();

I don't understand why this is necessary though. Anyone know a way to resolve this without using the "Include"?

解决方案

You are should use Expression to let EF provider parse your query.

Change the Func<User, bool> to Expression<Func<User, bool>>

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