具有多列和默认值的 Linq 左连接

Question

我对 linq 相当陌生，我需要连接两个具有以下要求的表:

应该左连接 t1 和 t2。

如果 t2 为空，则查询不应失败 - 应使用默认值。

我的查询:

var final = from t1 in saDist.AsEnumerable()
            from t2 in sapGrouped.AsEnumerable()
            where
                t1.Supplier.Id == t2.Supplier.Id && t1.VatRate == t2.VatRate
            select
                new
                {
                    t1.Supplier,
                    Amount = t1.Amount - t2.Amount,
                    Advance = t1.Advance - t2.Advance,
                    Balance = t1.Balance - t2.Balance,
                    t1.VatRate
                };

有人可以纠正这个吗？

Answer 1

这适用于Linqpad作为 C# 程序。

基本上，您的连接语法需要调整(请参阅 this )，并且您需要考虑何时没有任何内容可以连接到“t2”(因此我们进行空检查并在空时使用 0，否则 t2.金额等)

我创建了一些虚拟数据，以便您可以尝试一下。

参见http://codingsense.wordpress.com/2009/03/08/left-join-right-join-using-linq/再举一个例子。

我希望它能实现您想要的功能。

谢谢， 多米尼克

    public class A
    {
        void Main()
        {

            Distributor dist1 = new Distributor() { SupplierID = 1, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "A", DeptSupplierID = 1 };
            Distributor dist2 = new Distributor() { SupplierID = 2, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "B", DeptSupplierID = 1 };
            Distributor dist3 = new Distributor() { SupplierID = 3, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "C", DeptSupplierID = 1 };
            Distributor dist4 = new Distributor() { SupplierID = 4, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "D", DeptSupplierID = 2 };
            Distributor dist5 = new Distributor() { SupplierID = 5, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "E", DeptSupplierID = 2 };
            Distributor dist6 = new Distributor() { SupplierID = 6, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "F", DeptSupplierID = 2 };
            Distributor dist7 = new Distributor() { SupplierID = 7, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "G", DeptSupplierID = 6 };
            Distributor dist8 = new Distributor() { SupplierID = 8, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "H", DeptSupplierID = 3 };
            Distributor dist9 = new Distributor() { SupplierID = 9, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "I", DeptSupplierID = 3 };
            Distributor dist10 = new Distributor() { SupplierID = 10, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "J", DeptSupplierID = 7 };
            Distributor dist11 = new Distributor() { SupplierID = 11, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "K", DeptSupplierID = 7 };
            Distributor dist12 = new Distributor() { SupplierID = 12, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "L", DeptSupplierID = 5 };

            SAPGroup Dept1 = new SAPGroup() { SupplierID = 1, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "Development" };
            SAPGroup Dept2 = new SAPGroup() { SupplierID = 2, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "Testing" };
            SAPGroup Dept3 = new SAPGroup() { SupplierID = 3, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "Marketing" };
            SAPGroup Dept4 = new SAPGroup() { SupplierID = 4, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "Support" };

            List ListOfDistributors = new List();
            ListOfDistributors.AddRange((new Distributor[] { dist1, dist2, dist3, dist4, dist5, dist6, dist7,
    dist8, dist9, dist10, dist11, dist12 }));

            List ListOfSAPGroup = new List();
            ListOfSAPGroup.AddRange(new SAPGroup[] { Dept1, Dept2, Dept3, Dept4 });

            var final = from t1 in ListOfDistributors
                        join t2 in ListOfSAPGroup
                        on new { t1.SupplierID, t1.VatRateID } equals new { t2.SupplierID, t2.VatRateID }
                        into JoinedDistAndGrouped
                        from t2 in JoinedDistAndGrouped.DefaultIfEmpty()
                        select new
                        {
                            Name1 = t1.Name,
                            Name2 = (t2 == null) ? "no name" : t2.Name,
                            SupplierID = t1.SupplierID,
                            Amount = t1.Amount - (t2 == null ? 0 : t2.Amount),
                            Advance = t1.Advance - (t2 == null ? 0 : t2.Advance),
                            Balance = t1.Advance - (t2 == null ? 0 : t2.Balance),
                            VatRateID = t1.VatRateID
                        };

            final.Dump();
        }
    }


    class Distributor
    {
        public string Name { get; set; }
        public int SupplierID { get; set; }
        public int VatRateID { get; set; }
        public int DeptSupplierID { get; set; }
        public int Amount { get; set; }
        public int Advance { get; set; }
        public int Balance { get; set; }
    }

    class SAPGroup
    {
        public int SupplierID { get; set; }
        public int VatRateID { get; set; }
        public string Name { get; set; }
        public int Amount { get; set; }
        public int Advance { get; set; }
        public int Balance { get; set; }
    }

    public class Result
    {
        public string Name1 { get; set; }
        public string Name2 { get; set; }
        public int SupplierID { get; set; }
        public int Amount { get; set; }
        public int Advance { get; set; }
        public int Balance { get; set; }
        public int VatRateID { get; set; }
    }