EF Lambda How to make projection for GroupJoin - entity-framework

Question

I am trying to query EF models. (GameBank and GameCouponBank) How can I make a projection for left outer join (GoupJoin)?
Can I make projection for Coupons?
Here is my query
var gameBankResult = context.GameBanks.GroupJoin(context.GameCouponBanks, g => g.GameBankID, gc => gc.GameBankID,
(g,gc) => new {
g.quantity,
g.currency,
g.initiationResultCode,
g.productCode,
g.productDescription,
g.referenceId,
g.responseDateTime,
g.unitPrice,
g.totalPrice,
Coupons = gc
})
.Where(g => g.productCode == initiate.productCode)
.Select(s => s);
Here is models:
public class GameBank
{
public int GameBankID { get; set; }
public string referenceId { get; set; }
public string productCode { get; set; }
public int quantity { get; set; }
public string version { get; set; }
public DateTime? requestDateTime { get; set; } = DateTime.Now;
public int? customerID { get; set; }
public string password { get; set; }
public DateTime? responseDateTime { get; set; } = DateTime.Now;
public string initiationResultCode { get; set; }
public string companyToken { get; set; }
public int used { get; set; }
public string productDescription { get; set; }
public string currency { get; set; }
public double unitPrice { get; set; }
public double totalPrice { get; set; }
public virtual List<GameCouponBank> coupons { get; set; }
}
public class GameCouponBank
{
public int Id { get; set; }
public int GameBankID { get; set; }
public DateTime? expiryDate { get; set; }
public string Serial { get; set; }
public string Pin { get; set; }
}

Answer 1

You don't need to use GroupJoin explicitly. You can simply project your query as follows:
var gameBankResult = context.GameBanks.Where(g => g.productCode == initiate.productCode)
.Select(g => new {
g.quantity,
g.currency,
g.initiationResultCode,
g.productCode,
g.productDescription,
g.referenceId,
g.responseDateTime,
g.unitPrice,
g.totalPrice,
Coupons = g.coupons.Select(c => new {c.Id, c.GameBankID,...}).ToList() //<-- Here is the projection for coupons
}).FirstOrDefault(); // I assume you are returning single entity, if not then use `.ToList()` instead of `.FirstOrDefault()`