c# - Entity-Framework Editing a many-to-many table -

i'm designing application table keep track of transportation.

i have 4 tables:

create table [dbo].[trips] (     [tripid] int not null primary key identity,     ... ) create table [dbo].[drivers] (     [driverid] int not null primary key identity,     ... ) create table [dbo].[vehicles] (     [vehicleid] int not null primary key identity,     ... ) , 1 table called vehicletrip  create table [dbo].[vehicletrip] (     [tripid] int not null ,      [vehicleid] int not null,      [driverid] int not null,      primary key ([tripid], [vehicleid], [driverid]),      constraint [fk_tripids_trips] foreign key (tripid) references trips(tripid),      constraint [fk_vechicleid_vehicles] foreign key (vehicleid) references vehicles(vehicleid),      constraint [fk_driverid_driverid] foreign key (driverid) references drivers(driverid) ) 

using ef, i'm trying edit record in vehicletrip

public class tripvm {     public int tripid { get; set; }     public int vehicleid { get; set; }     public int driverid { get; set; }     //other fields  public void insertupdate() {     var vehicletrip = new studenttransportation.data.model.vehicletrip         {             //uses classes values create new object             tripid = tripid,             vehicleid = vehicleid,             driverid = vehicleid         };      context.vehicletrip.attach(vehicletrip);     context.entry(vehicletrip).state = entitystate.modified;     context.savechanges(); } 

however, appears if ef doesn't save record.

one option retrieve original entity (the 1 trying update) create new entity new values , update using following code:

context.entry(originalentity).currentvalues.setvalues(newentitywithnewvalues); 

and of course save changes.