在 LINQ 查询中使用组

Question

我正在使用 LINQ to CRM 提供商。

我正在查询信息，然后使用 LINQ 来查询 LINQ to CRM 查询，以便我可以使用 GroupBy，因为 LINQ to CRM 提供程序不支持它。这是我到目前为止所拥有的。

var linqQuery = (from r in orgServiceContext.CreateQuery("opportunity")
    join c in orgServiceContext.CreateQuery("contact") on 
        ((EntityReference)r["new_contact"]).Id equals c["contactid"] into opp
    from o in opp.DefaultIfEmpty()
    select new
    {
        OpportunityId = !r.Contains("opportunityid") 
            ? string.Empty : r["opportunityid"],
        CustomerId = !r.Contains("customerid") 
            ? string.Empty : ((EntityReference)r["customerid"]).Name,
        OwnerId = !r.Contains("ownerid") 
            ? string.Empty : ((EntityReference)r["ownerid"]).Id.ToString(),
        OwnerName = !r.Contains("ownerid") 
            ? string.Empty : ((EntityReference)r["ownerid"]).Name.ToString(),
        Priority = !r.Contains("opportunityratingcode") 
            ? string.Empty : r.FormattedValues["opportunityratingcode"],
        ContactName = !r.Contains("new_contact") 
            ? string.Empty : ((EntityReference)r["new_contact"]).Name,
        // ...
        // other properties  
    });

var linqQuery2 = (from f in linqQuery.ToList()
                  group f by f.OwnerId into myGroup
                  select new
                  {
                      OrderCount = myGroup.Count()
                  });

但我还希望能够从 linqQuery2 查询 linqQuery2 中的其他变量。

所以我想要这样的东西：

var linqQuery2 = (from f in linqQuery.ToList()
                  group f by f.OwnerId into myGroup
                  select new
                  {
                      OwnerName = myGroup.OwnerName,
                      OrderCount = myGroup.Count()
                  });

这可能吗？

Answer 1

假设组中所有项目的 OwnerNames 都是相同的，那么您可以执行以下操作：

var linqQuery2 = (from f in linqQuery.ToList()
    group f by f.OwnerId into myGroup
    select new
    {
        OwnerName = myGroup.First().OwnerName,
        OrderCount = myGroup.Count()
    });

编辑：

如果您想多次使用第一个项目，我建议您使用“let”操作员：

var linqQuery2 = (from f in linqQuery.ToList()
                    group f by f.OwnerId into myGroup
                    let first = myGroup.First()
                    select new
                    {
                        OwnerName = first.OwnerName,
                        OrderCount = myGroup.Count()
                    });

Answer 2

交替尝试

        var linqQuery2 = (from f in linqQuery.ToList()
                          group f by f.OwnerName
                          into myGroup
                          select new
                                     {
                                         OwnerName = myGroup.Key,
                                         OwnerCount = myGroup.Count()
                                     });

：

        var linqQuery2 = linqQuery.ToList()
            .GroupBy(f => f.OwnerName)
            .Select(myGroup => new
                                {
                                    OwnerName = myGroup.Key,
                                    OwnerCount = myGroup.Count()
                                });