C#-LINQ-扩展方法

Question

什么是以下LINQ的扩展方法等效？

var qry = from a in context.A_Collections
          from b in context.B_Collections
          where a.PK == b.PK
          select 
        new {
              A_key = a.PK, 
              A_Value = a.Value,
              B_Key = b.PK,
              B_value = b.value
            };

我的意思是

(不完全的)

var query = context.A_Collections.
                Where(
                      a => a.PK == context.B_Collections.Select(b => b.PK)).
                    Select(
                            x => new { 
                                      A_key = a.Pk,
                                      A_Value = a.Value,
                                      B_Key = b.PK,
                                      B_value = b.value
                                     }
                           );

Answer 1

后续的"from"子句转换为SelectMany调用:

var qry = context.A_Collections
                 .SelectMany(a => context.B_Collections,
                             (a, b) => new { a, b })
                 .Where(x => x.a.PK == x.b.PK)
                 .Select(x => new { A_key = x.a.PK,
                                    A_value = x.a.Value,
                                    B_key = x.b.PK,
                                    B_value = x.b.Value });

"x"位是由于引入了透明标识符.

请注意,调用Join可能比使用更有效SelectMany(取决于具体情况),但这是您开始使用的查询的更直接的翻译.