updating a database record with linq to sql in c#

Question

I have a function that looks like this:

public UpdateRecord(MyObjectModel TheObject, int TheUserID)
{
  using (MyDataContextModel TheDC = new MyDataContextModel())
  {
     var TheObjectInDB = (from o in TheDC.TheObjects
                          where o.ObjectID == TheObject.ObjectID
                          select new MyObjectModel()).SingleOrDefault();

     if (TheObject.Prop1 != null) { TheObjectInDB.Prop1 = TheObject.Prop1; }
     if (TheObject.Prop2 != null) { TheObjectInDB.Prop2 = TheObject.Prop2; }

     TheDC.SubmitChanges();
  }
}

The code is not crashing but it's not updating the DB. What do I need to change?

Answer 1

select o instead of new MyObjectMode(), Modify:

var TheObjectInDB = (from o in TheDC.TheObjects
                          where o.ObjectID == TheObject.ObjectID
                          select o).SingleOrDefault();

Answer 2

First of all you do select new MyObjectModel() in your query which will always create a new object regardsess of what you pull from the database. Change that to select o .

Secondly, in:

if (TheObject.Prop1 != null) { TheObjectInDB.Prop1 = TheObject.Prop1; }
if (TheObject.Prop2 != null) { TheObjectInDB.Prop2 = TheObject.Prop2; }

you update the object's values conditionally. So if Prop1 and Prop2 are null the object's properties won't be updated.

Answer 3

The following code works and it is almost the same as what you posted.

DataContext dc = new DataContext(ConnectionString);
var q = from a in dc.GetTable<Employee>()
        where a.EmployeeID == this.EmployeeID
        select a;
Employee temp = q.Single<Employee>();
temp.EmployeeActiveStatus = this.EmployeeActiveStatus;
temp.EmployeeName = this.EmployeeName;
temp.EmployeeUserID = this.EmployeeUserID;
temp.EmployeeCreateModifyDate = this.EmployeeCreateModifyDate;
temp.EmployeePaperWork = this.EmployeePaperWork;
dc.SubmitChanges();

The only major difference that I see is the line: select new MyObjectMode()).SingleOrDefault()