MongoDb中的继承:如何请求已定义类型的实例 [英] Inheritance in MongoDb: how to request instances of defined type

问题描述

这是我过去在实体框架(POCO)中利用继承的方式:

This is how I used to utilize inheritance in Entity Framework (POCO):

ctx.Animals // base class instances (all instances)
ctx.Animals.OfType<Cat>  // inherited class Cat's instances only
ctx.Animals.OfType<Dog> // inherited class Dog's instances only

这是我在MongoDb中找到的唯一类似方法( MongoDb参考):

This is the only similar way I found in MongoDb (MongoDb reference):

var query = Query.EQ("_t", "Cat");
var cursor = collection.FindAs<Animal>(query);

请注意，在后一种情况下，我必须处理鉴别符("_t")并硬编码我的类名，这不太方便，而且看起来很糟糕.如果我错过查询，则会在尝试枚举时遇到异常.我错过了什么吗?我的建议是文档Db，它按原样"存储对象，应该很容易处理继承.

Note in the latter case I have to deal with discriminator ("_t") and hardcode my class name, that is not quite convenient and looks awful. If I miss the query I got an exception on enumeration attempt. Have I missed something? My suggestion was the document Db which stores objects 'as is' should handle inheritance easily.

推荐答案

假设您的鉴别功能正常(每个文档的_t存储正确)，那么我认为这就是您要寻找的.

Assuming your discriminators are functioning (_t is stored correctly for each document) then I think this is what you are looking for.

var results = collection.AsQueryable<Animal>().OfType<Cat>

仅返回猫"类型的那些文档.

Returns only those documents that are of type 'Cat'.

这篇关于MongoDb中的继承:如何请求已定义类型的实例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！