Using Group in LINQ Query

问题

I am using the LINQ to CRM provider.

I am querying the information then I am using LINQ to query the LINQ to CRM query so I can use GroupBy, since the LINQ to CRM provider does not support it. This is what I have so far.

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()
                  });

But I also want to be able to query the other variables that are in linqQuery from linqQuery2.

So I would want something like:

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

Is this possible to do?

回答1:

Assuming the OwnerNames will be identical for all the items in the group then you could do something like:

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

Edit:

If you want to use the first item multiple times, I'd suggest you use the 'let' operator:

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()
                    });

回答2:

Try

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

Alternately:

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

来源：https://stackoverflow.com/questions/7642365/using-group-in-linq-query