实体框架对象引用是否等于相同的数据库对象 [英] Do entity framework object references equal for same database objects

问题描述

如果我从不同的地方在逻辑上"(在数据库中)查询同一对象，那么实体框架是否会返回相同的对象引用.

Does entity framework return the same object reference if I query the "logically" (in database) same object from different places.

例如，我查询了名为Joe Black的客户(并假设现在我知道数据库中只有一个Joe Black.) Customer c = select ... blabla where ... Name == Joe Black...;和代码中的其他地方，我查询了Customer c2 = select... where.. ID==5，其中5是Joe Black的ID.我知道在数据库中它们映射到相同的对象，但是在代码级它们也映射到相同的对象吗?那么c1等于c2吗?我有要合并的列表，并检查对象的逻辑相等性(我现在无法访问数据库)，我想知道Entity Framework对象是否可以很好地发挥作用，还是应该编写自定义比较器类.

For example, I queried customer with name Joe Black, (and assume for now I know that there's only one Joe Black in the database.) Customer c = select ... blabla where ... Name == Joe Black...; and in somewhere else in the code, I queried Customer c2 = select... where.. ID==5 where 5 is the ID of Joe Black. I know that in the database they map to the same object, but DO they also map to the same object in code level? So does c1 equal to c2? I have lists to merge and check for logical equality of the objects (I cannot access the database for now) and I was wondering whether Entity Framework objects will play nicely with it or should I write my custom comparer classes.

推荐答案

大多数ORM(包括实体框架和NHibernate)都使用此处为例.

Most ORMs, including Entity Framework and NHibernate, use the Identity Map Pattern to ensure there is only a single instance of a given entity per primary key. The identity map is scoped by the context, so two different contexts will create two objects which refer to the same entity. It is a good practice to have entities implement IEquatable, including overrides for equality operators so that '==' or '!=' will work. This is more involved than what one might think. Take a look here for an example.

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