实体框架-有条件地包括相关实体 [英] Entity Framework - Conditionally include related entities

问题描述

我维护一个API，该API根据对人员列表的请求，根据该请求返回不同的结果集。例如，一些API客户端想要获取人员列表及其交互的列表，而其他API客户端则需要人员及其元数据的列表。所有这些都可以在请求返回人的API方法中指定。

I maintain an API that, based on a request for a list of people, returns a different result set based on the request. For example, some API clients want to get a list of people and a list of their interactions, others want people and a list of their metadata. All this can be specified int he request to the API method that returns people.

这似乎不起作用：

using (var dbcontext = new ExampleEntities())
{
    var query = dbcontext.People.AsQueryable();
    //determined in earlier application logic based on request
    if(includeMetadata)
    {
        query = query.Include("metadata");
    }
    //determined in earlier application logic based on request
    if(includeInteractions) 
    {
        query = query.Include("interactions");
    }
    /* ...SNIP... */
}

我不想这样做：

var query = dbcontext.People.Include("Metadata").Include("interactions");

这意味着每一个获取人的请求都将包括其所有相关实体，即使请求API客户不需要它们。

which will mean every request to get a person will include ALL their related entities, even if the requesting API client does not need them.

我也不想编写逻辑的每种可能组合：

I also don't want to code every possible combination of logic:

if(includeMetadata && includeInteractions)
{
    var query = dbcontext.People.Include("Metadata").Include("interactions");

}
else if(includeMetadata)
{
    var query = dbcontext.People.Include("Metadata");
}
else if(includeInteractions)
{
    var query = dbcontext.People.Include("Interactions");
}
else
{
    var query = dbcontext.People;
}

这将导致难以维护的代码，但是，我意识到

This will result in hard-to-maintain code, however, I realize I could code generate this if needed.

推荐答案

您可以链接IQueryable的

You can chain the IQueryable's

using (var dbcontext = new ExampleEntities())
{
    var query = dbcontext.People.AsQueryable();
    if(includeMetadata)
    {
        query = query.Include("metadata");
    }
    if(includeInteractions) 
    {
        query = query.Include("interactions");
    }    
}

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