EF5 code first with ASP.NET Web API: Update entity with many-to-many relationship

Question

I'm trying to update a Customer in my database using ASP.NET Web API and Entity Framework 5 code-first, but it's not working. My entities look like this:

public class CustomerModel
{
    public int Id { get; set; }
    public string Name { get; set; }

    // More fields

    public ICollection<CustomerTypeModel> CustomerTypes { get; set; }
}

public class CustomerTypeModel
{
    public int Id { get; set; }
    public string Type { get; set; }

    [JsonIgnore]
    public ICollection<CustomerModel> Customers { get; set; }
}

Nothing all that special. I've built a web interface where users can add a customer by supplying the name and checking one or more customer types. When hitting the submit button, the data is sent to my Web API method:

public void Put([FromBody]CustomerModel customer)
{
    using (var context = new MyContext())
    {
        context.Customers.Attach(customer);
        context.Entry(customer).State = EntityState.Modified;
        context.SaveChanges();
    }
}

This updates the customer fields, but the related customer types are ignored. The incoming customer object does contain a list of CustomerTypes it should be associated with:

[0] => { Id: 1, Type: "Finance", Customers: Null },
[1] => { Id: 2, Type: "Insurance", Customers: Null }
[2] => { Id: 3, Type: "Electronics", Customers: Null }

But instead of looking at this list and adding/removing associated entities, EF just ignores it. New associations are ignored and existing associations remain even if they should be deleted.

I had a similar problem when inserting a customer into the database, this was fixed when I adjusted the state of these entities to EntityState.Unchanged. Naturally, I tried to apply this same magic fix in my update scenario:

public void Put([FromBody]CustomerModel customer)
{
    using (var context = new MyContext())
    {
        foreach (var customertype in customer.CustomerTypes)
        {
            context.Entry(customertype).State = EntityState.Unchanged;
        }

        context.Customers.Attach(customer);
        context.Entry(customer).State = EntityState.Modified;
        context.SaveChanges();
    }
}

But EF keeps displaying the same behavior.

Any ideas on how to fix this? Or should I really just do a manual clear to the list of CustomerTypes and then manually add them?

Thanks in advance.

JP

Answer 1

This is not really solvable by only setting entity states. You must load the customer from the database first including all its current types and then remove types from or add types to the loaded customer according to the updated types collection of the posted customer. Change tracking will do the rest to delete entries from the join table or insert new entries:

public void Put([FromBody]CustomerModel customer)
{
    using (var context = new MyContext())
    {
        var customerInDb = context.Customers.Include(c => c.CustomerTypes)
            .Single(c => c.Id == customer.Id);

        // Updates the Name property
        context.Entry(customerInDb).CurrentValues.SetValues(customer);

        // Remove types
        foreach (var typeInDb in customerInDb.CustomerTypes.ToList())
            if (!customer.CustomerTypes.Any(t => t.Id == typeInDb.Id))
                customerInDb.CustomerTypes.Remove(typeInDb);

        // Add new types
        foreach (var type in customer.CustomerTypes)
            if (!customerInDb.CustomerTypes.Any(t => t.Id == type.Id))
            {
                context.CustomerTypes.Attach(type);
                customerInDb.CustomerTypes.Add(type);
            }

        context.SaveChanges();
    }
}