转换SQL Distinct，Count＆amp; GroupBy到带有Navigation的Linq查询

Question

我在LINQ中有这个查询，其中query是来自表LeadSales的预定义IQueryable ...

var results = from q in query
    select new LeadBuyersByStateItem {
        ContactID = q.SoldToContactID,
        FirstName = q.Contact.FirstName,
        LastName = q.Contact.LastName
     };

它工作正常，但我需要稍微调整一下。我在SQL中也有这个：

SELECT
    SoldToContactID, 
    COUNT (SoldToContactID) AS Count
FROM
    LeadSales
GROUP BY 
    SoldToContactID

按预期方式返回此数据集：

所以现在，我需要将LINQ查询转换为GROUP BY，并包含Count，当然还要保存导航，以便我可以访问FirstName和LastName。

我遇到LINQ语法问题......

var results = from q in query
    group q by q.SoldToContactID into g
    select new LeadBuyersByStateItem {
        ContactID = ?.SoldToContactID,
        FirstName = ?.Contact.FirstName,
        LastName = ?.Contact.LastName
        ContactCount = ????
     };

只是我们......

public class LeadBuyersByStateItem
{
    public int ContactID { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int ContactCount { get; set; }
}

Answer 1

我认为这就是你要找的东西：

var results = from q in query
    group q by new {q.SoldToContactID,
                    FirstName=q.Contact.FirstName,
                    LastName=q.Contact.LastName} into g
    select new LeadBuyersByStateItem {
        ContactID = g.Key.SoldToContactID,
        FirstName = g.Key.FirstName,
        LastName = g.Key.LastName,
        ContactCount = g.Count()
     };

您需要使用匿名类型

按多个列进行分组