Question

我有三个对象（splistitemcollection）加入到一起工作很好，但我遇到的问题是合同对象和客户对象之间存在一对多的关系。我需要在加入期间仅抓取每个合同对象的第一个客户对象。

这是我得到的

(Contract)(Customer)
12345  John Smith
12345  Jane Smith
67890  howard Jones
67890  Mary Jones

这就是我想要的 12345（只是其中一个客户，简或约翰）

这是我目前正在使用的代码。

  var joinedResults = from SPListItem contracts in _contractList
                      join SPListItem customers in _customerList
                      on contracts["ContractNumber"] equals customers["ContractNumber"]  
                      join SPListItem loans in _loanList
                      on contracts["ContractNumber"] equals loans["Contract_x0020_Number"] 
                      into l from loans in l.DefaultIfEmpty()
                      select new MergedData(contracts, customers, loans);

在SQL中，我在我的连接中定义的子查询中定义了一个select top子句，我只是不能理解我的新手linq大脑的语法。

最终结果

  var joinedResults = from SPListItem contracts in _contractList
      join SPListItem customers in 
      // Derived subset
        (from SPListItem customers in _customerList
        group customers by customers["ContractNumber"] into groupedCustomers 
        select groupedCustomers.FirstOrDefault()
      )  on contracts["ContractNumber"] equals customers["ContractNumber"]  
      join SPListItem loans in _loanList
      on contracts["ContractNumber"] equals loans["Contract_x0020_Number"] into l
      from loans in l.DefaultIfEmpty()
      select new MergedData(contracts, customers, loans);

Answer 1

我先解释一下，因为LINQ有时会让人感到困惑。我们的想法是让您的客户进行查询，并按ContractNumber进行分组，然后采取第一个。如果你想要你可以通过某个领域订购，让它更具确定性（总是按字母顺序排列最低的名称等）然后你加入你的tempQuery基本上是不同的（ContractNumber）和第一个客户。

var tempQuery =  from SPListItem customers in _customerList
    group customers by customers["ContractNumber"] into gby 
    select gby.First();


var joinedResults =

    from SPListItem contracts in _contractList
    join SPListItem customer in tempQuery
on contract["ContractNumber"] equals customer["ContractNumber"]
    join SPListItem loans in _loanList
on contracts["ContractNumber"] equals loans["Contract_x0020_Number"] 
into l from loans in l.DefaultIfEmpty()
select new MergedData(
     contracts, 
     customer, 
     loans
   );

}

Answer 2

var joinedResults =   (from SPListItem contracts in _contractList
                      join SPListItem customers in _customerList
                      on contracts["ContractNumber"] equals customers["ContractNumber"]  
                      join SPListItem loans in _loanList
                      on contracts["ContractNumber"] equals loans["Contract_x0020_Number"] 
                      into l from loans in l.DefaultIfEmpty()
                      select new MergedData(contracts, customers, loans)).FirstOrDefault();

只需调用FirstOrDefault方法即可选择找到的第一个项目。

Answer 3

这就像返回的每个合同的Top（1）点查询：

var joinedResults = from SPListItem contracts in _contractList
                      join SPListItem loans in _loanList
                      on contracts["ContractNumber"] equals loans["Contract_x0020_Number"] 
                      into l from loans in l.DefaultIfEmpty()
                      select new MergedData(contracts, 
                      customer = _customerList.Where( c => c["ContractNumber"] == contracts["ContractNumber"].FirstOrDefault()
                      , loans);

LINQ加入前1名

3 个答案: