Most efficient way to update with LINQ to SQL

Question

Can I update my employee record as given in the function below or do I have to make a query of the employee collection first and then update the data?

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Answer 1

You cannot attach a modified entity to a DataContext when there is no RowVersion column. Instead you could store original entity in your application as long as maintaining a copy for data changes. Then when changes need to be saved you could attach original entity to a DataContext, change its values to match the modified entity values and submit changes.

Here is an example:

public int updateEmployee(App3_EMPLOYEE employee, App3_EMPLOYEE originalEmployee)
{
    DBContextDataContext db = new DBContextDataContext();
    db.App3_EMPLOYEEs.Attach(originalEmployee);

    // TODO: Copy values from employee to original employee

    db.SubmitChanges();
    return employee.PKEY;
}

Update:

There is a table in the database with columns ID, Name, Notes

// fetch an employee which will not be changed in the application
Employee original;
using(var db = new TestDbDataContext())
{
  original = db.Employees.First(e => e.ID == 2);
}

// create an instance to work with
var modified = new Employee {ID = original.ID, Name = original.Name, Notes = original.Notes};

// change some info
modified.Notes = string.Format("new notes as of {0}", DateTime.Now.ToShortTimeString());  
// update
using(var db = new TestDbDataContext())
{
  db.Employees.Attach(original);
  original.Notes = modified.Notes;
  db.SubmitChanges();
}