ASP.NET 核心 Web API - FirstOrDefault 在实体框架中没有给出所需的结果

Question

In ASP.NET Core 5 Web API, I have these models:

public abstract class AuditableBaseEntity
{
    [Key]
    public long Id { get; set; }
}

public class Merchant : AuditableBaseEntity
{
    public string MerchantName { get; set; }
    public string AccountNumber { get; set; }
    public string UserName { get; set; }
}

Then these are the queries:

Get the UserName of the Logged in User

var userName = _userResolverService.GetUserName();

Get the id of the merchant

var merchantId = _context.merchants
                         .Where(u => u.UserName == userName)
                         .Select(m => m.Id)
                         .FirstOrDefault();

I expect to get the Id of a particular merchant using the logged in UserName , but I got zero (0) result

When I debut userName returns the correct result. The problem is with getting the merchantId .

How do I get this resolved?

Thanks

Answer 1

When you execute only a part of your command, what do you get:

var merchant = _context.merchants.Where(u => u.UserName == userName).FirstOrDefault();
var merchantId = merchant.Id;

If merchant == null, it will then return the default value for int (id), which is 0.