EntityFramework 6如何通过反射获取身份字段? [英] EntityFramework 6 How to get identity-field with reflection?

问题描述

我有一个类型参数为T的通用方法，其中T是EF模型中实体的类型. 我需要获取这种类型的识别字段的名称. 我看到了这篇文章:是否可以通过反射或其他方式获取实体ID字段的名称? 但是我不明白Tevin在谈论 EntitySetBase 和 EntityTypeBase 类型时在说什么. 如果 EntityTypeBase 是模型中实体之一的类型，则EF6没有属性 KeyMembers .

I have a generic method with type parameter T, where T is the type of entity in EF model. I need to get the name of identifying field in this type. I saw this article: Is there a way to get entity id-field's name by reflection or whatever? But I can't understand, what Tevin talking about when he talks about EntitySetBase and EntityTypeBase types. If EntityTypeBase is type of one of the entities in model, so then EF6 have no property KeyMembers.

推荐答案

我认为不可能仅通过反射来获取主键.

I don't think it's possible to get the primary keys only by reflection.

首先，让我们了解EF如何确定哪些属性将成为主键，而与顺序/优先级无关

First, let's find out how EF determine which property(ies) that will be primary key(s) regardless of the order / priority

• 通过公约

主键的实体框架约定为:

The Entity Framework convention for primary keys is:

1. 您的类定义了一个名称为"ID"或"Id"的属性
2. 或类名后跟"ID"或"Id"

我们可以使用GetProperties并比较属性名称.

We can use GetProperties and compare the property name.

var key = type.GetProperties().FirstOrDefault(p => 
    p.Name.Equals("ID", StringComparison.OrdinalIgnoreCase) 
    || p.Name.Equals(type.Name + "ID", StringComparison.OrdinalIgnoreCase));

• 通过 [KeyAttribute] >
• By [KeyAttribute]

我们可以使用CustomAttributes并比较属性类型.

We can use CustomAttributes and compare the attribute type.

var key = type.GetProperties().FirstOrDefault(p => 
    p.CustomAttributes.Any(attr => attr.AttributeType == typeof(KeyAttribute)));

• 通过 Fluent Api

这是很难做到的，modelBuilder封装在OnModelCreating中，即使我们将modelBuilder保存为字段/属性，仍然很难从HasKey函数中提取密钥，一切都被封装.您可以检查源代码. EF中的所有内容都取决于 ObjectContext ，然后调用ObjectContext，例如下面的代码行，

This is the one that's difficult to do, modelBuilder is encapsulated in the OnModelCreating and even if we save the modelBuilder somewhere as field/property, it's still difficult to extract the key from HasKey function, everything is encapsulated. You can check the source code. And everything in EF depends on ObjectContext and once the ObjectContext is called, for example this line of code,

((IObjectContextAdapter)context).ObjectContext

然后将建立与数据库的连接，您可以使用探查器进行检查.这是源代码的摘录.

then a connection to the database will be made, you can check using profiler. And here is the code excerpt of the source code.

public override ObjectContext ObjectContext
{
    get
    {
        Initialize();
        return ObjectContextInUse;
    }
}

public void Initialize()
{
    InitializeContext();
    InitializeDatabase();
}

因此，当前获取主键的唯一可能方法是通过对象集，实体集，键成员等，如

Therefore, currently the only possible way to get the primary key(s) is through object set, entity set, key members, etc as explained in this post

var keyNames = set.EntitySet.ElementType.KeyMembers.Select(k => k.Name);

这篇关于EntityFramework 6如何通过反射获取身份字段?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！