1. 

　　

using (Db1Context db = new Db1Context())
            {
                using (var tran = db.Database.BeginTransaction())
                {
                    //db operation
                    result = db.SaveChanges();
                    using (Db2Context db2 = new Db2Context(db.Database.Connection,false))//必须false
                    {
                        db2.Database.UseTransaction(db.Database.GetDbTransaction());
                        //db2 operation
                        db2.SaveChanges();
                    }
                    tran.Commit();
                }
            }

 

2.  TransactionScope