Protect property value from changing after first creation Entity Framework Code First

Question

What is the best way to prevent a property from changing after it was added to the database?

I know I can do it by tracking state when I am actually using the DbContext in the application. But then it's up to the programmer.

I would like this to be included in a DbContext override or inside the model configuration. Then it would work automatically and reject the change when someone tries to update the property.

One way to solve it would be by overriding ValidateEntity and check it there, but I am wondering if this is the best solution

Moho · Accepted Answer · 2013-10-19 14:10:21Z

1

Implement the property in your entity class with your own backing variable (old school) and a flag denoting whether or not the property has already been set once:

    private DateTime _created;
    private bool _createdSet = false;

    public DateTime Created 
    {
        get
        {
            return _created;
        }
        set
        {
            if (_createdSet)
            {
                throw new InvalidOperationException("Property 'Created' cannot be changed once set");
            }

            _createdSet = true;
            _created = value;
        }
    }

answered Oct 19, 2013 at 14:10

Moho

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1 Comment

plasticide Over a year ago

this solution seems to be the simplest.

Daniel Leiszen · Accepted Answer · 2013-10-19 14:44:13Z

1

You can put it in the model by making the property setter private. As far as I know EF maps private properties as well. Or you can create a public property (ignored in map) based on a private property (mapped) and put the logic there. If the model is not in your hand then it should be in the context as you mentioned. ValidateEntity sounds to be a right place but honestly I have no experience doing such thing.

EDIT: I tryied the following

public class Entity
{
    public int Id { get; set; }
    public string Code { get; private set; }

    public string MyCode 
    { 
        get { return this.Code; }
        set
        {
            if (string.IsNullOrEmpty(this.Code))
            {
                this.Code = value;
            }
        }
    }
}

And in the context OnModelCreating

modelBuilder.Entity<Entity>()
    .ToTable("dbo.Entity")
    .HasKey(s => s.Id);

modelBuilder.Entity<Entity>()
    .Property(s => s.Code)
    .IsRequired();

modelBuilder.Entity<Entity>()
    .Ignore(s => s.MyCode);

And it works.

edited Oct 19, 2013 at 14:44

answered Oct 19, 2013 at 14:08

Daniel Leiszen

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6 Comments

Moho Over a year ago

but EF can't set the property on load from the DB, so this doesn't work

Sander Over a year ago

Thanks! I guess I could make the setter private and then have a seperate factory method to create the entity that takes the set-once property value as a parameter allowing to update the private field

Sander Over a year ago

From Julie Lerman's book: Entity Framework will use reflection to access a nonpublic setter, this means that the context will be able to populate restricted properties when materializing objects as a result of a query or an insert. So this seems to handle it. I will give it a try

Daniel Leiszen Over a year ago

Yes, that's correct EF uses reflection just as DataContractSerializer can instantiate objects without calling the constructor, or set private properties. Furthermore, I think they use an internal version of reflection with even more privileges.

Moho Over a year ago

I still prefer my solution, however, as it informs the 'user' of an invalid operation. This solution hides the fact that the user can't change the value.

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