Partially updating an entity in EF6

Question

I'm trying to figure out how to smoothly do a partial update (basically a HTTP PATCH) of an entity, using Entity Framework 6.0, but I'm stumped at the number of examples out there that don't seem to work for me (even those that aren't obviously for another version of EF).

What I'd like to accomplish:

• The entity is updated without having to load it first; i.e. there's only one trip to the database
• Only the properties that I touch are updated - others are left as is

The closest I've gotten is neatly described by this answer to a very similar question, and illustrated by the following code:

public async Task UpdateMyEntity(int id, int? updatedProperty, string otherProperty)
{
    using (var context = new MyDbContext())
    {
        var entity = new MyEntity { Id = id };
        context.MyEntities.Attach(entity);

        if (updatedProperty != null) { entity.Property = updatedProperty.Value; }
        if (!string.IsNullOrEmpty(otherProperty) { entity.OtherProperty = otherProperty; }

        await context.SaveChangesAsync();
    }
}

Now, this works for simple entities, but I'm getting entity validation errors because I have a couple of required properties and relations that are not updated and therefore not present in the attached entity. As noted, I'd just like to ignore those.

I've debugged and verified that context.Entry(entity).Property(e => e.Property).IsModified changes to true when that line is run, and that all the properties I never touch still return false for similar checks, so I thought EF would be able to handle this.

Is it possible to resolve this under the two constraints above? How?

---

Update:

With LSU.Net's answer I understand somewhat what I have to do, but it doesn't work fully. The logic fails for referential properties.

Consider the following domain model:

public class MyEntity
{
    public int Id { get; set; }
    public int Property { get; set; }
    [Required]
    public string OtherProperty { get; set; }
    [Required]
    public OtherEntity Related { get; set; }
}

public class OtherEntity
{
    public int Id { get; set; }
    public string SomeProperty { get; set; }
}

Now, if I try to update a MyEntity, I do the following:

var entity = new MyEntity { Id = 123 }; // an entity with this id exists in db
context.MyEntities.Attach(entity);

if (updatedProperty != null) { entity.Property = updatedProperty.Value; }

await context.SaveChangesAsync();

In my custom validation method, overridden as in the answer below, the validation error on the required property OtherProperty is correctly removed, since it is not modified. However, I still get a validation error on the Related property, because entityEntry.Member("Related") is DbReferenceEntry, not DbPropertyEntry, and thus the validation error is not marked as a false error.

I tried adding a separate, analogous clause for handling reference properties, but the entityEntry doesn't seem to mark those as changed; with relation = member as DbReferenceEntry, relation doesn't have anything to indicate that the relationship is changed.

What can I check against for false errors in this case? Are there any other cases I need to handle specially (one-to-many relationships, for example)?

Answer 1

Entity Framework validation with partial updates

@Shimmy has written some code here to omit the validation logic for unmodified properties. That may work for you.

protected override DbEntityValidationResult ValidateEntity(
  DbEntityEntry entityEntry,
  IDictionary<object, object> items)
{
  var result = base.ValidateEntity(entityEntry, items);
  var falseErrors = result.ValidationErrors
    .Where(error =>
    {
      var member = entityEntry.Member(error.PropertyName);
      var property = member as DbPropertyEntry;
      if (property != null)
        return !property.IsModified;
      else
        return false;//not false err;
    });

  foreach (var error in falseErrors.ToArray())
    result.ValidationErrors.Remove(error);
  return result;
}