Linq Select column if data exits-CodePudding

I have a method that returns data by viewing models from multiple tables. The problem occurs when I try to select a column while data is not exiting. Heres my code

public async Task<List<CustomerViewModel>> GetCustomers()
{
    return await _context.Customers.Select(x => new CustomerViewModel
    {
        Id = x.Id,
        Name = x.Name,
        Phone = x.Phone,
        Address = x.Address,
        Payment = x.Payment,
        Due = x.Due,
        Received = x.Received,
        DateOfReg = x.DateOfReg,
        Quantity = _context.BSells.Where(_ => _.CustomerId == x.Id).Select(_=>_.Quantity).Sum(),
        Unitcost = _context.BSells.Where(_ => _.CustomerId == x.Id).FirstOrDefault().UnitPrice
    }).ToListAsync();
}

The problem occurs on lines 14, and 15 because the BSell table doesn't have data of the particular customer. Now, what should I do now?

I may not be able to express the problem clearly. Sorry for that.

CodePudding user response：

Alright I've solved the issue by changing code little bit

public async Task<List<CustomerViewModel>> GetCustomers()
{
    return await _context.Customers.Select(x => new CustomerViewModel
    {
        Id = x.Id,
        Name = x.Name,
        Phone = x.Phone,
        Address = x.Address,
        Payment = x.Payment,
        Due = x.Due,
        Received = x.Received,
        DateOfReg = x.DateOfReg,
        Quantity = _context.BSells.Where(_ => _.CustomerId == x.Id).Select(_=>_.Quantity).Sum(),
        Unitcost = _context.BSells.Where(_ => _.CustomerId == x.Id).Select(_ => _.UnitPrice).FirstOrDefault()
    }).ToListAsync();
}

I should have selected the column before taking the first value. Is it? I will be really grateful if anyone addresses my mistakes. Thank you.