How do you update one object of a has_many :through relationship

rubyonrails-talk
1

Hi guys.

How do you update nested attributes for one object of a has_many :through relationship? So I have an entity model and this model can have many fact_values. The difference between fact and fact_value is that the latter has an extra value attribute. This is because facts can be common among many entities, but each entity can have its own unique value for a specific fact. So my models are the following:

class Entity   has_many :fact_values   has_many :facts, :through => :fact_values end

class FactValue   belongs_to :entity   belongs_to :fact end

class Fact   has_many :fact_values   has_many :entities, :through => :fact_values end

Now I've specified that Entity accepts_nested_attributes_for :fact_values. But I want it to accept nested attributes for a single (pre-defined) fact_value and update only that fact_value. The way I'm going about it right now is to have a virtual attribute in my Entity model representing that one fact_value and update that fact_value in the entity controller. I'm wondering if there is any automatic way to accomplish what I'm trying to do?

Thanks!

2

I'm not sure exactly what the problem is. If you only want to update one object, you only put that object in the fields_for(:fact_values) part of the form. If you're worried about the wrong object being created/updated through accepts_nested_attributes, then the :reject_if can enable you to add validation.

3

Perhaps something along the lines of

class Entity

  has_many :fact_values   has_many :facts, :through => :fact_values   belongs_to :anointed_fact_value

   accepts_nested_attributes_for :fact_values, :reject_if => :not_updatable_fact_value

   def not_updatable_fact_value(attrs)       attrs[:id] != anointed_fact_value_id    end end

4

I’m using formtastic, I see that it seems simple enough with the standard rails forms. I suppose I can ask on a formtastic gorup to see what they say.

Thanks