Question

我是linq的新手可以帮助我将以下查询转换为linq。

   SELECT A.Name,
   Sum(C.MoneyIN) - Sum(C.MoneyOut) AS Balance
   FROM   Customers A
   JOIN   Banks B ON A.Id = B.id
   JOIN   BankTransactions C ON B.Id = C.BankID
   GROUP  BY A.Name

我尝试将其转换为linq

var query =  from c in db.Customers
                     join b in db.Banks on c.Id equals b.CustomerId
                     join bt in db.BankTransactions on b.Id equals bt.BankId                         
                     group c by c.Name into Cust                         
                     select new
                     {
                         Name = c.Name,
                         Balance = Cust.Sum(bt.MoneyIn) - Cust.Sum(bt.MoneyOut) 
                     };

有人可以告诉我哪里错了吗？

提前致谢。

Answer 1

试试：

var query =  from c in db.Customers
                     join b in db.Banks on c.Id equals b.CustomerId
                     join bt in db.BankTransactions on b.Id equals bt.BankId                         
                     group bt by c.Name into Cust                         
                     select new
                     {
                         Name = Cust.Name,
                         Balance = Cust.Sum(x => x.MoneyIn) - Cust.Sum(x => x.MoneyOut) 
                     };

似乎问题是，在上次选择时您使用了c.Name，但应该Cust.Name，因为您已经执行了分组。

更新1。

此外Cust.Sum(bt.MoneyIn) =＆gt; Cust.Sum(x => x.MoneyIn)。

更新2。

你也是错误的道具分组。如果您想将总和应用于您的BankTransactions，您需要将其分组，如：

将c.Name分组 bt 到Cust

所以工作示例可能如下：

public class Customer
        {
            public int Id { get; set; }
            public string Name { get; set; }
        }

        public class Bank
        {
            public int CustomerId { get; set; }
            public int Id { get; set; }
        }

        public class BankTransaction
        {
            public int BankId { get; set; }
            public int MoneyIn { get; set; }
            public int MoneyOut { get; set; }
        }

编译的查询：

var customers = new List<Customer>();
            var banks = new List<Bank>();
            var bankTransactions = new List<BankTransaction>();

            var result = from c in customers
                join b in banks on c.Id equals b.CustomerId
                join bt in bankTransactions on b.Id equals bt.BankId                         
                group bt by c.Name into Cust
                select new { Name = Cust.Key, Balance = Cust.Sum(x => x.MoneyIn) - Cust.Sum(x => x.MoneyIn) };

Answer 2

总之，您需要使用对象的别名。请参阅Sum() here，如果MoneyIn和MoneyOut是int则必须使用this overload

Chnage this：

Balance = Cust.Sum(bt.MoneyIn) - Cust.Sum(bt.MoneyOut)

到此：

Balance = Cust.Sum(x=>x.bt.MoneyIn) - Cust.Sum(x=>x.bt.MoneyOut)

Name的{{1}}是分组的键：

Cust

完整查询：

select new
      {
        Name = Cust.Key,
        Balance = Cust.Sum(x => x.bt.MoneyIn) - Cust.Sum(x => x.bt.MoneyOut) 
      };

使用sum with group by将Sql Query转换为linq

2 个答案: