Linq Group on Multiple Fields - VB.NET, Anonymous, Key

问题

I am stumped. I need help. I have a DTO object with duplicates patient address data. I need to get only the unique addresses.

Dim PatientAddressDto = New List(Of PatientAddress)

{Populate PatientAddressDto with lots of duplicate data}

PatientAddressDto = (From d In PatientAddressDto
                    Group d By PatientAddressDtoGrouped = New PatientAddress With {
                                                              .Address1 = d.Address1,
                                                              .Address2 = d.Address2,
                                                              .City = d.City,
                                                              .State = d.State,
                                                              .Zip = d.Zip
                                                              }
                  Into Group
                  Select New PatientAddress With {
                                                  .Address1 = PatientAddressDtoGrouped.Address1,
                                                  .Address2 = PatientAddressDtoGrouped.Address2,
                                                  .City = PatientAddressDtoGrouped.City,
                                                  .State = PatientAddressDtoGrouped.State,
                                                  .Zip = PatientAddressDtoGrouped.Zip
                                                  }).ToList()

I have tried the following with no luck:

PatientAddressDto = (From d In PatientAddressDto
                    Select New PatientAddress With {
                                                  .Address1 = d.Address1,
                                                  .Address2 = d.Address2,
                                                  .City = d.City,
                                                  .State = d.State,
                                                  .Zip = d.Zip
                                                    }).Distinct     

and also

PatientAddressDto = PatientAddressDto.GroupBy(Function(p) New PatientAddress With {
                                                  .Address1 = p.Address1,
                                                  .Address2 = p.Address2,
                                                  .City = p.City,
                                                  .State = p.State,
                                                  .Zip = p.Zip
                                                    })

回答1:

You can use an anonymous type and make use of the Key keyword in order for equality to behave the way you expect (not required for C#).

Change your grouping by specifying the Key prefix and remove the PatientAddress usage :

Group d By PatientAddressDtoGrouped = New With {
    Key .Address1 = d.Address1,
    Key .Address2 = d.Address2,
    Key .City = d.City,
    Key .State = d.State,
    Key .Zip = d.Zip
}

回答2:

I have found the following code to work which essentially accomplishes the grouping that I desire and populating the new object as type PatientAddress therefore eliminating the use of anonymous objects and the keyword Key.

Maybe someone can explain it, at the moment I can not. Have a nice day.

Dim PatientAddressDto = New List(Of PatientAddress)

{Populate PatientAddressDto with lots of duplicate data}

PatientAddressDto = (From d In PatientAddressDto
                    Group d By d.Address1,
                                d.Address2,
                                d.City,
                                d.State,
                                d.Zip Into g =
                    Group Let grp = New PatientAddress With {.Address1 = Address1,
                                                                .Address2 = Address2,
                                                                .City = City,
                                                                .State = State,
                                                                .Zip = Zip}
                    Select grp).ToList()

回答3:

Its probably because PatientAddress does not override GetHashCode and Equals. An alternative is to us an anonymous type for the grouping. Try writing:

Group d By PatientAddressDtoGrouped = New With { Key .Address1 = d.Address1, ....

来源：https://stackoverflow.com/questions/9997001/linq-group-on-multiple-fields-vb-net-anonymous-key