LINQ - Left Join And Group By - linq

Question

I have a problem. This is my products class
public int ProductID { get; set; }
public string ProductName { get; set; }
public int CategoryID { get; set; }
public decimal Price { get; set; }
public int CompanyID { get; set; }
public string QuantityPerUnit { get; set;
And this is OrderDetail Class
public int DetailID { get; set; }
public int OrderID { get; set; }
public int ProductID { get; set; }
public decimal UnitPrice { get; set; }
public int Quantity { get; set; }
public bool Discount { get; set; }
so ı wrote this query in mssql. So, how can I write this query on linq ?
select Products.ProductID, Sum(OrderDetails.Quantity) as 'NumberOfOrdered' from Products
left join OrderDetails on Products.ProductID = OrderDetails.ProductID
group by Products.ProductID
order by Products.ProductID
I Wrote this query but it doesn't work.
from p in _context.Products
join d in _context.OrderDetails on p.ProductsID equals d.ProductsID into t1
from d1 in t1.DefaultIfEmpty()
group new { p, d } by new { p.ProductsID, d.ProductsID } into g
orderby g.Key.ProductsID
select new ProductsOrderDetails
{
ProductsID = g.Key.ProductsID,
QuantityToplam = g.(x=>x.d.Quantity)
}).ToList();

Answer 1

So you have Products, and OrderDetails. Every Product has zero or more OrderDetails, every OrderDetail is the detail of exactly one Product, namely the Product that OrderDetail.ProductId belongs to.
Requirement: From every Product, give me the Id and the sum of the Quantities of all its OrderDetails
Whenever you need the sequence of items, every item with its sub-items, like Schools with their Students, Authors with their Books, Orders with their OrderDetails, consider using one of the overloads of Enumerable.GroupJoin
In this case, I don't want a simple Product with its OrderDetails, I want to compose a special result. For every Product I want the Id and the sum of Quantities of all its OrderDetauls. Therefore I use the Overload with a parameter resultSelector.
var result = dbContext.Products.GroupJoin( // GroupJoin Products
dbContext.OrderDetails, // with Orderdetails
product => product.Id, // From every Product take the Id
orderDetail => orderDetail.ProductId, // From every OrderDetail that the foreign key
// resultSelector: for every Product and all its zero or more OrderDetails
// create one new object
(product, orderDetailsOfThisProduct) => new
{
Id = product.Id,
QuantitiesToPlam = orderDetailsOfThisProduct
.Select(orderDetail => orderDetail.Quantity)
.Sum(),
});
For property QuantitiesToPlam: for every OrderDetail that belongs to this Product: take the value of property Quantity, and Sum them.