Entity Framework 5: Using DatabaseGeneratedOption.Computed option - ef-code-first

Question

I have an EF5 code first project that uses the [DatabaseGenerated(DatabaseGeneratedOption.Computed)] attribute.
This option is overriding my settings.
Consider this SQL table:
CREATE TABLE Vehicle (
VehicleId int identity(1,1) not null,
Name varchar(100) not null default ('Not Set')
)
I am using the SQL default construct to set the [Name] is case it is not set.
In code behind, I have a class defined similar to:
public class Vehicle {
...
[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
public string ShoulderYN { get; set; }
}
When I update the entity in code, the value set in the default overrides my new setting.
In code, I have (pseudo):
vehicle.Name = 'Update Name of Vehicle';
_dbContext.Update(vehicle);
_dbContext.SaveChanges();
The expected result is Vehicle.Name = 'Update Name of Vehicle'.
The actual result is Vehicle.Name = 'Not Set'.
Is there a way in EF5 to say:
if Vehicle.Name is null/empty, use the value defined in the database? Otherwise, if I set the value in code, I want to use this value.

Answer 1

Apparently, no there isn't. It's not that smart :)
As you may already read, Computed option just tells the EF not to update your column, because you will compute a value on the DB-side yourself. EF will then just return newly computed value from your database (which in your case is "Not Set").
Your basic three options are - as per EF Source code documentation:
None - The database does not generate values.
Identity - The database generates a value when a row is inserted.
Computed - The database generates a value when a row is inserted or updated.
https://github.com/aspnet/EntityFramework6/blob/527ae18fe23f7649712e9461de0c90ed67c3dca9/src/EntityFramework/DataAnnotations/Schema/DatabaseGeneratedOption.cs
Since you expect a little more custom logic to be done, I'm afraid you would have to do it yourself. I would suggest you stop relying on database default constraint and do everything in code first approach. This way you would have a code like that:
public class Vehicle
{
public Vehicle()
{
this.Name = "Not set";
}
// Without 'Generated' attribute
public string Name { get; set; }
}
This way, when your Entity is created, it automatically starts with expected default value. And can be later changed by simply modifying the Name property.
Hope it helps!

Answer 2

Actually there is a simple solution for this:
You need to leave default constraint with value in table creation script as it is now:
CREATE TABLE Vehicle (
VehicleId int identity(1,1) not null,
Name varchar(100) not null default ('Not Set')
)
Just remove DatabaseGenerated attribute from property in class definition:
public class Vehicle {
...
[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
public string ShoulderYN { get; set; }
}
And that's it: now database will use default value only if you do not specify some value in code. Hope this helps.

Answer 3

I checked this for hours to get good answer but no:
EF cannot update models by automatic generated-ID.
You have 3 options:
Adding another VehicleId to Vehicle model.
Change automatic generated-ID to be manual generated by you.
Setting unique identifier to be something else then the generated-ID in your
model.
In your Vehicle Class it can be the Name property.
I suggest you option 3:
Setting up unique-id to be Vehicle.Name (and you can add more properties).
Then: if vehicle by unique-id doesn't exists, add new vehicle to db-context:
//if there is no such a Vehicle in system, add it:
if (vehicle.Name !=null && vehicle.Name != String.Empty && _dbContext.Where(v => v.Name == vehicle.Name).FirstOrDefault() == null)
_dbContext.Add(vehicle);
_dbContext.SaveChanges();