Question

我有3个表，试图通过左连接将它们组合在一起。在我的应用程序中，所有LINQ表达式都是查询链格式（lambda表达式）。

我正在尝试弄清楚如何使用LINQ完成此查询；

这是我的SQL查询；

select i.INVOICE_NUMBER, ic.CustomerName, o.BusinessUnit
from Invoices_Daily as i
left join intercompany as ic on i.customer_number = ic.customernumber
left join ordertypes as o on i.LINE_ORDERTYPE = o.OrderType

我已尝试如下组合GroupJoin；

var commissions = data
    .GroupJoin(genericNameList,
        d => d.CUSTOMER_NUMBER,
        g => g.CustomerId,
        (d, g) => new { d, generic = g.FirstOrDefault() })
    .GroupJoin(intercompanies,
        dd => dd.d.CUSTOMER_NAME,
        i => i.CustomerId,
        (d, i) => new { data = d.d, intercompanies = i.FirstOrDefault() })
    .Select(_ => new MainGridViewModel
    {
        INVOICE_DATE = _.d.INVOICE_DATE,
        EndCustomer = _.generic == null ? _.d.CUSTOMER_NAME : _.generic.EndCustomer ?? _.d.CUSTOMER_NAME,
        LINE_ORDERTYPE = _.i.OrderType
    })
    .ToList();

但是我遇到下面的语法错误；

错误CS0411无法从用法中推断出方法'Enumerable.GroupJoin（IEnumerable，IEnumerable，Func，Func，Func，TResult>）'的类型参数。尝试显式指定类型参数。

Answer 1

我根据请求编写了一个测试示例，显示了正确的语法，这应该都可以正常工作。

public class Data
{
    public string CUSTOMER_NUMBER { get; set; }
    public string CUSTOMER_NAME { get; set; }
}

public class NameList
{
    public string CustomerId { get; set; }

}

public class InterCompanies
{
    public string CustomerId { get; set; }
}

public class Test
{
    public void TMP()
    {
        var data = new List<Data>();
        var genericNameList = new List<NameList>();
        var intercompanies = new List<InterCompanies>();

        var commissions = data
            .GroupJoin(genericNameList,
                d => d.CUSTOMER_NUMBER,
                g => g.CustomerId,
                (d, g) => new { d, generic = g.FirstOrDefault() })
            .GroupJoin(intercompanies,
                dd => dd.d.CUSTOMER_NAME,
                i => i.CustomerId,
                (d, i) => new { data = d.d, intercompanies = i.FirstOrDefault() })
            .ToList();
    }
}

我最初的想法是您CUSTOMER_NUMBER和CUSTOMER_NAME是错误的，因为为什么您在同一类中有2个字段具有相同的值。但是，既然您向我保证它们是正确的，也许您正在交换联接中数据上预期的字段顺序，因此很难看到数据模型。

也许您的第二次加入应如下所示：

.GroupJoin(intercompanies,
            dd => dd.d.CUSTOMER_NUMBER,
            i => i.CUSTOMER_NAME,

使用Lambda语法的C＃LINQ Multiple GroupJoin

1 个答案: