如何使用 Entity Framework Core 从所有消息的数据库中获取用户对话框列表

Question

I have a table in the database with messages, namely:

| Id | FromId | ToId | Text | Date | Read |

Here's what the class looks like:

public class Message
{
    public int Id { get; set; }
    public IdentityUser From { get; set; }
    public IdentityUser To { get; set; }
    public string Text { get; set; }
    public DateTime Date { get; set; }
    public bool Read { get; set; }
}

I need to form a request to get a list of all the user's dialogs using the Entity Framework Core. I've sketched out a sample SQL query:

SELECT FromId, MAX(Date) as updated_at, sum(Read) as new_messages 
FROM (SELECT FromId, Date, Read 
FROM Messages 
WHERE ToId = 'f3578a36-208c-4504-8f3c-afa564455537' 
UNION SELECT ToId, Date, 0 
FROM Messages 
WHERE FromId = 'f3578a36-208c-4504-8f3c-afa564455537' 
ORDER BY Date DESC) as talks 
GROUP BY FromId 
ORDER BY Date DESC;

where `f3578a36-208c-4504-8f3c-afa564455537" is the Id of the user whose dialog list I want to get.

However, I can't execute it using the Entity Framework (or don't know how). Is there any way to do this using only EF? I use SQLite.

Answer 1

Using EF I would write it down like this, I'd query separately for messages from and to user and group them appropriately:

var chatsFromUser = dbContext.Messages
    .Where(m => m.From.Id == "f3578a36-208c-4504-8f3c-afa564455537")
    .GroupBy(m => m.To.Id);
var chatsToUser = dbContext.Messages
    .Where(m => m.To.Id == "f3578a36-208c-4504-8f3c-afa564455537")
    .GroupBy(m => m.From.Id);

But, I would also suggest that you should define ID s properties for users in Message entity class:

public class Message
{
    public int Id { get; set; }
    public IdentityUser From { get; set; }
    // choose appropiate type, GUID maybe?
    public string FromId { get; set; }
    public IdentityUser To { get; set; }
    // choose appropiate type, GUID maybe?
    public string ToId { get; set; }
    public string Text { get; set; }
    public DateTime Date { get; set; }
    public bool Read { get; set; }
}

Then query would be slightly simplified as you could access IDs directly from message object:

var chatsFromUser = dbContext.Messages
    .Where(m => m.FromId == "f3578a36-208c-4504-8f3c-afa564455537")
    .GroupBy(m => m.ToId);
var chatsToUser = dbContext.Messages
    .Where(m => m.ToId == "f3578a36-208c-4504-8f3c-afa564455537")
    .GroupBy(m => m.FromId);