从数组返回值

Question

I have Inventories table and here I save all ProductId's who is below 10 or the same as 10 in Array

public int[] OrderNow()
{
    return context.Inventory.Where(u => u.Quantity <= 10).Select(i =>i.ProductId)
                                                         .ToArray();
}

I know I have 3 products that Quantity is below 10 and when I run debug I can see those Ids. So far so good.

But When I want to retrieve names of those products, I just can get one of those 3 products...

To get names of those Products I wrote this code, but it's returning only one Product name.

public string[] ProductName()
{
     var prId = OrderNow();
     foreach (var p in prId)
     {

       return context.Products.Where(u => u.ProductId == p)
                              .Select(p => p.ProductName).ToArray();
          // After one loop it's jumping foreach process .. I don't know why
     }
     return null; // I don't know what to write here, but I must to return something
}

Edited with a similar problem...

public int[] OrderNow()
{
    return context.Inventory.Where(u => u.Quantity <= 10).Select(i =>i.DepartmentId)
                                                         .ToArray();
}

And my User email

public string[] UserEmails()
{
   var departmentIds= OrderNow();   // Gets the array of product ids

   return context.Users
         .Where(u => u.IsInventoryAdmin == true)
                 .Where(u => departmentIds.Contains(u.DepartmentId)) // Here failing
                 .Select(e => e.Email)
                 .ToArray();    
}

Answer 1

Because you are returning inside the loop. So when the loop executes for the first item in the prId array, it gets only that product ( Basically a collection with only that product ) and since you have the return statement, it will be returned(exiting that code block).Your loop iteration will not be executed for the remaining items in the array.

You should use Contains method. This allows you to query the Products which has ProductId matching to items inside the array ( the productIds you got from OrderNow method)

public string[] ProductName()
{
   var productIds= OrderNow();   // Gets the array of product ids

   return context.Products
                 .Where(u => productIds.Contains(u.ProductId))
                 .Select(p => p.ProductName)
                 .ToArray();    
}