Linq to SQL ADD and Update - winforms

Question

As you can tell from my code, I'm absolute a beginner. After searching through other similar issues on LINQ to SQL problems, I find myself still seemingly stuck on two objectives. 1) Adding a new entry with input from the user selection from three comboboxes and a datepicker and 2) Updating an existing database entry using interactions from the datagridview.
My windows form datagridview is displaying the following output
**select b.Date, a.EmployeeName,
c.ProjectName, b.Hours
from dbo.Employees a
left outer join dbo.EmployeeProjectHours b
on a.EmployeeId = b.EmployeeId
left outer join dbo.Projects c
on b.ProjectId = c.ProjectId**
Here is my ADD method the user is providing me with ProjectName, EmployeeName, Date and Hours. Any thoughts for a layman would be appreciated.
I don't get an error running the insert, but nothing is added to my dab as well
using (ProjectHoursDataContext dbInsert = new ProjectHoursDataContext())
{
this.Validate();
EmployeeProjectHour empHours = new EmployeeProjectHour();
empHours.Date = dateDateTimePicker.Value;
empHours.Hours = Convert.ToDecimal(hoursComboBox.Text);
empHours.ProjectId = dbInsert.Projects.First(p => p.ProjectName == projectNameComboBox.Text).ProjectId;
empHours.EmployeeId = dbInsert.Employees.First(m => m.EmployeeName == employeeNameComboBox.Text).EmployeeId;
db.EmployeeProjectHours.InsertOnSubmit(empHours);
dbInsert.SubmitChanges();
}
Here is my Update attempting to use updates directly from the datagridview. I get the following error: A first chance exception of type 'System.ArgumentException' occurred in System.Windows.Forms.dll
using (ProjectHoursDataContext dbUpdate = new ProjectHoursDataContext())
{
this.Validate();
dataGridView1.AutoGenerateColumns = true;
projectBindingSource.DataSource = dbUpdate;
projectBindingSource.DataMember = "Updates";
projectBindingSource.EndEdit();
dbUpdate.SubmitChanges();
}

Answer 1

My best guess so far is, you want to edit and change existing Employee, Project and EmployeeProjectHours records.
So you would do:
using (ProjectHoursDataContext dbInsert = new ProjectHoursDataContext())
{
this.Validate();
// Get the records
Employee emp = new Employee();
Project proj = new Project();
EmployeeProjectHour empHours = new EmployeeProjectHour();
// Set new values to Employees tables
emp = dbInsert.Employees
.First(m => m.EmployeeName == employeeNameComboBox.Text);
//just get the empployee
//setting values will update it
emp.EmployeeName = employeeNameComboBox.Text;
// GET an existing project
proj = dbInsert.Projects
.First(p => p.ProjectName == projectNameComboBox.Text);
//update its values.
proj.ProjectName = projectNameComboBox.Text;
proj.ProjectDescription = "Test";
//GET an empHours
empHours = dbInsert.Projects.First(p => p.EmployeeId == emp.EmployeeId &&
p.ProjectId == proj.ProjectId);
//set its values
empHours.Date = dateDateTimePicker.Value;
empHours.Hours = Convert.ToDecimal(hoursComboBox.Text);
dbInsert.SubmitChanges();
}

Answer 2

Aside from the new code below, I also set my increment status for my projects database to NO. I had set it yes from a previous stackoverflow discussion. Thanks
public void AddInfo()
{
db.Connection.Open();
this.Validate();
EmployeeProjectHour empHours = new EmployeeProjectHour();
empHours.Date = dateDateTimePicker.Value;
empHours.Hours = Convert.ToDecimal(hoursComboBox.Text);
empHours.ProjectId = db.Projects.First(p => p.ProjectName == projectNameComboBox.Text).ProjectId;
empHours.EmployeeId = db.Employees.First(m => m.EmployeeName == employeeNameComboBox.Text).EmployeeId;
db.EmployeeProjectHours.InsertOnSubmit(empHours);
db.SubmitChanges();
db.Connection.Close();
}