Linq实体框架 - 让所有客户看到ID不在很多表中

Question

I have 2 tables:

Customer

Car

and many-to-many table MM, which stores:

Customer_Id Car_Id

How do I get all Customers which Car_Id's are not in many to many table?

I tried like this:

public async Task<IEnumerable<CustomerModel>> GetNewCustomersForCar(int carId)
        {
            var sentCustomers = await _unit.Repository<Car>().Queryable()
                .SelectMany(a => a.AspNetUsers, (b, a) => new { b, a })
                .Where(b => b.Id == carId)
                .Select(ba => new CustomerModel()
                {
                    Id = ba.a.Id,
                    Email = ba.a.Email
                })
                .ToListAsync();

            var allCustomers = await _unit.Repository<AspNetUser>().Queryable()
                .Select(c => new CustomerModel()
                {
                    Id = c.Id,
                    Email = c.Email
                }).ToListAsync();

            return allCustomers.Where(ac => !sentCustomers.Contains(ac));

So basically I select all customers for selected car, then I check all customers, and in the end I select from all customers that do not contain Id's from many to many customer table for selected customer.

Get all customers which didn't use car yet(all that used car are having id's for selected car in many to many table).

Answer 1

if you have a Cars navigation property in your AspNetUser entity, you could do this:

var query= await _unit.Repository<AspNetUser>()
                      .Queryable()
                      .Where(u=>!u.Cars.Any(c=>c.Id==carId))
                      .Select(c => new CustomerModel()
                                    {
                                        Id = c.Id,
                                        Email = c.Email
                                    })
                      .ToListAsync();

Also you can change your Where to .Where(u=>u.Cars.All(c=>c.Id!=carId)) ,could be more readable