如何使LEFT JOIN在Lambda LINQ表达式中 [英] How to make LEFT JOIN in Lambda LINQ expressions

问题描述

如何使此表达式为LEFT JOIN

How to make this expression as LEFT JOIN

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

推荐答案

这是使用lambda表达式更复杂的方法写：

And this is the more complicated way using lambda expressions to write it:

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
         }
   )

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