How to set null value to an existing attribute on Entity Framework

Question

Scenario:
I have an entity with a (nullable) FK Id that it's not required anymore.

Problem:
When I update this entity on the context, setting NULL to the FK, after the SaveChanges() the value is not persisted on the db.

Any ideas?

Edit #1:
After the SaveChanges, I checked the base and continues the old value, and if I change to other value works fine.

Class:

public class Account
{
    [Required]
    public int Id { get; set; }

    public int? PlanId { get; set; }

    [Required]
    public virtual Status Status { get; set; }

    #region Navigations Properties

    public virtual Plan Plan { get; set; }

    #endregion
}

Usage: (Problem)

Account ent = Context.Set<Account>().AsQueryable().FirstOrDefault(x => x.Id = id);
ent.PlanId = null;
Context.SaveChanges();

Edit [PROBLEM SOLVED]

It was necessary to send an array with the fields that would get null as the new value.

public virtual void Update(TEntity entityToUpdate, List<string> updateNullFields)
{
    DbSet.Attach(entityToUpdate);
    foreach (var item in updateNullFields)
    {
        Context.Entry(entityToUpdate).Property(item).IsModified = true;
    }
}

Did you just make the FK nullable in your class without changing the database? — Eric J.
– Eric J., Commented May 5, 2016 at 18:53
EF6, having exactly the same problem, cannot understand why. Interesting, if before saving the changes I assign null to the property in the Immediate Window, the property correctly sets to null. — Alexey
– Alexey, Commented Jun 30, 2016 at 5:03

jon.r · Accepted Answer · 2016-05-05 19:59:44Z

1

I would say you most likely did not update the database itself. Once you update the database using this code:

ALTER TABLE [table_name] ALTER COLUMN [fk_column] [datatype] NULL

Run 'Update Model from Database' on the .edmx file.

Make sure this Nullable = true

edited May 5, 2016 at 19:59

answered May 5, 2016 at 19:06

jon.r

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3 Comments

Alexis Diel Over a year ago

I'm using Migration to maintain the DB, and the FK already is nullable... the problem it's on EF that not persist the null value on the db after the attribute has any non-null value.

jon.r Over a year ago

Is this on a save or edit action? You should check the entity state to make sure the object is modified before inserting/updating it.

Alexis Diel Over a year ago

I've to pass these fields that i want to force the null value, to set it as IsModified = true; after i Attach. ` DbSet.Attach(entityToUpdate); foreach (var item in updateNullFields) { Context.Entry(entityToUpdate).Property(item).IsModified = true; } `

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