How do I update a value in table A when creating a row in table B?

Question

My platform has two tables UserInfo and PersonalInfo. When a user creates a profile the data is saved in UserInfo. The view for UserInfo has an @Html.EditorFor, which is auto populated from Active Directory(if the AD field is null, a helper class adds N/A in its place). Depending on what application the user decides to use within the platform, more information will be needed so they will need to create a row in PersonalInfo. The view for PersonalInfo as a @Html.DropDownListFor that the user can choose from which will update that users department and cost center.

I would like to update the department for UserInfo when the row for PersonalInfo is created or updated.

Currently when I create a row it looks like this:

if (ModelState.IsValid)
{
var myUserInfo = new myUserInfo
{
    UserId = userNum.Id,
    Address = viewModel.Address,
    City = viewModel.City,
    State = viewModel.State,
    CellPhone = viewModel.CellPhone,
    Department = viewmodel.Department,
    CostCenter = viewmodel.CostCenter,
    ZipCode = viewModel.ZipCode
};
db.MyUserInfos.Add(myUserInfo);
db.SaveChanges();
} 

How do I update the Department field only in the PersonalInfo table before db.SaveChanges() is called?

Answer 1

add a row in tableB:-

var tableB = new TableB
{
    UserId = userNum.Id,
    Address = viewModel.Address,
    City = viewModel.City,
    State = viewModel.State,
    CellPhone = viewModel.CellPhone,
    Department = viewmodel.Department,
    CostCenter = viewmodel.CostCenter,
    ZipCode = viewModel.ZipCode
};
db.MyTableB.Add(tableB);

update a row in tableA:-

var tableA = db.MyTableA.Find(tableAId);

tableA.Department = viewModel.Department;

db.MyTableA.Attach(tableA);
db.Entry(tableA).State = EntityState.Modified

once you have made all the your required changes, call db.SaveChanges();