c# - linq中的左外连接

Question

我有以下查询，但我不知道如何在表 1 上进行左外连接。

var query = (from r in table1
             join f in table2
                 on r.ID equals f.ID
             select new
             {     
                 r.ID, 
                 r.FirstName,
                 r.LastName,
                 FirstNameOnRecord = 
                     (f != null ? f.FirstName : string.Empty),
                 LastNameOnRecord = 
                     (f != null ? f.LastName : string.Empty),
                 NameChanged = 
                     (f != null 
                         ? (f.FirstName.CompareTo(r.FirstName) == 0 
                             && f.LastName.CompareTo(r.LastName) == 0) 
                         : false)
             }).ToList();

Answer 1

引用this或 this了解更多信息的示例和您的案例将是这样的-

var query = from r in table1
            join f in table2
            on r.ID equals f.ID into g
            from f in g.DefaultIfEmpty()
             select new
             {     
                r.ID
                , r.FirstName
                , r.LastName
                , FirstNameOnRecord = (f != null ? f.FirstName : string.Empty)
                , LastNameOnRecord = (f != null ? f.LastName : string.Empty)
                , NameChanged = (f != null ? (f.FirstName.CompareTo(r.FirstName) == 0 
                &&  f.LastName.CompareTo(r.LastName) == 0) : false)
              }).ToList();