How to update only one row from inserted

Question

The entity:

  public class Feature { 
     public int Id {get;set;}
     public int DeviceId {get;set;}
     public string Value {get;set;}
     public bool IsPrimary {get;set;}
   }

The story:

Each device has a list of features. But only one of them could be primary.

Value of 'IsPrimary' could be changed:

• WebAPI sets to 'true' after creation if device has not got any primary feature in db
• Could be changed by user manualy

There are a lot of parallel requests. And when they executes and device hasn't got featues all these parallel requests creates 'IsPrimary'=true feature.

How do handle this situation?

Answer 1

I would handle it a bit differently: the IsPrimary should be a property of the device, not the Feature. Something like this:

public class Device
{
    public List<Feature> Features { get; set; }
    public Feature PrimaryFeature { get; set; }
    // ...
}

public class Feature 
{ 
    public int Id { get; set; }
    public int DeviceId { get; set; }
    public string Value { get; set; }
}

Also you should implement some concurrency checks: https://msdn.microsoft.com/en-ca/data/jj592904.aspx

So if two users try to modify the same Device at the same time, one of them will get an error, and he/she can act accordingly. Or you can handle the concurrency issue however you feel appropriate.

This might be a bit more helpful: http://www.asp.net/mvc/overview/getting-started/getting-started-with-ef-using-mvc/handling-concurrency-with-the-entity-framework-in-an-asp-net-mvc-application

Answer 2

Set a flag where you write the record in the database and check if there is a property in the table that already has IsPrimary = true. This way you won't have multiple IsPrimary records in your database. And then the user can switch the primary feature between the existing records.