c# - 如何在 Lambda LINQ 表达式中创建 LEFT JOIN

Question

如何使这个表达式成为 LEFT JOIN

var query = order.Items.Join(productNonCriticalityList,
    i => i.ProductID,
    p => p.ProductID,
    (i, p) => i);

Answer 1

这是使用 lambda 表达式编写的更复杂的方法:

order.Items
   .GroupJoin (
      productNonCriticalityList, 
      i => i.ProductID, 
      p => p.ProductID, 
      (i, g) => 
         new  
         {
            i = i, 
            g = g
         }
   )
   .SelectMany (
      temp => temp.g.DefaultIfEmpty(), 
      (temp, p) => 
         new  
         {
            i = temp.i, 
            p = p
         }
   )