瓶颈使用实体框架继承 [英] bottleneck using entity framework inheritance

问题描述

所以我的实体

问题我想有一个页面与所有的故事标题和他们的类型

the problem i want to have a page with all the story titles and their types

有三个故事 LongStory ， CoOpStory ， GenericStory

通用故事与通用故事类型的 StoryType 相关联

the generic story is associated with StoryType for the type of the generic story

我有两个问题

首先我想检查故事是否 LongStory 或 CoOpStory 我必须得到所有的实体，并检查实体类型，如果它是 LongStory 然后做某事，我不知道如何检索一些数据[只有标题]，并检查类型

first when i want to check if the story is LongStory or CoOpStory i have to get all the entity and check the entity type if it is LongStory then do something , i don't know how to retrieve some data [only the title] and check the type

我的第二个问题，就像我说我想要有一个页面，所有的故事标题和他们的类型，我不知道如何做到这一点没有做很多查询，我不能加入到 StoryType 表beca使用它必须是 GenericStory 与之相关联，所以我先做所有的故事，然后对每个 GenericStory 获取类型

my second problem like i said i want to have a page with all the story titles and their types i don't know how to do that without making a lot of queries , i can't make a join to the StoryType table because it must be GenericStory to be associated with that , so what i do first get all the stories then do an extra query for every GenericStory to get the type

推荐答案

您正在查看 OfType 和 Concat 扩展方法。

You are looking of OfType and Concat extension methods.

只需要调用LongStory实例：

To get only LongStory instances you just need to call:

var longStories = context.Stories.OfType<LongStory>().ToList();

要获得更大的查询，它有点复杂。您可以尝试：

To get your bigger query it is little bit more complex. You can either try:

var allStories = context.Stories
                        .OfType<GenericStory>()
                        .Include("StoryType") // I'm not sure how this works with concat
                        .Concat(
                             context.Stories.OfType<LongStory>.Concat(         
                                  context.Stories.OfType<CoOpStory>()));

或者您可以做一个投影：

Or you can do a projection:

var allStories = context.Stories
                        .OfType<GenericStory>()
                        .Select(s => new { s.Title, s.StoryType.Name })
                        .Concat(
                             context.Stories
                                    .OfType<LongStory>
                                    .Select(s => new { s.Title, "LongStory" })
                                    .Concat(         
                                        context.Stories
                                               .OfType<CoOpStory>()
                                               .Select(s => new { s.Title, Type })));

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