列表中的 Linq select 具有 2 个多对多关系

Question

I have the following database structure:

USER <--> [user_client] <--> CLIENT <--> [client_application] <--> APPLICATION

USER, CLIENT and APPLICATION tables contain unique keys. user_client and client_application are many-to-many tables to map USERs to CLIENTs and CLIENTs to APPs.

I am using MVC5 / C#. The many-to-many tables are hidden in my Model by the Entity Framework.

What I want to achieve is the following: for a given USER, which has a list of CLIENTs, get the combined list of the distinct APPLICATIONs that all his CLIENTs have.

Could you please help with the logic and the Linq query (preferably in fluent syntax if possible)? Is it possible to do it in a single query without looping through the list of clients?

Thank you in advance.

Reda

Answer 1

不确定它是否与您的架构匹配，但是

user.clients.SelectMany(c => c.applications).Distinct()

Answer 2

The key is to use SelectMany instead of Select which will give you a IEnuerable<Application> instead of a IEnumerable<IEnumerable<Application>>

var user = context.Users.Where(u => u.Id == 1).Single();
var applications = user.Clients
    .SelectMany(c => c.Application)
    .GroupBy(a = a.Id)
    .Select(a => a.First());

Answer 3

I want to collaborate to this question, not providing an exact solution, but additional information.

I applied @tafia answer to my own problem, but with a slight modification to the SelectMany method. I replaced it with just Select .

File selectedFile = _unitOfWork.FileRepository.GetById(idFile)
selectedFile.FilePaper.Select(c => c.Paper).Distinct().ToList()

You can read about the difference between Select and SelectMany , here .

I applied my modified solution on the following group of tables:

Though your table seems to be different:

I'm not sure if that solution proposed by @tafia works there.

PS. If you want to make the middle tables appear in EF, a possible "fix" is adding a primary key to them ( id ).