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POHow to save attributes to a has_many :through join table with no existing records to build from
 

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  1. POHow to save attributes to a has_many :through join table with no existing records to build from
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    <p>I have a form which creates a new Child record and a new Parent record using <code>accepts_nested_attributes_for</code></p> <p>Children and Parents have a <code>has_many :through</code> association like so:</p> <pre><code>class Child &lt; ActiveRecord::Base has_many :relationships has_many :parents, through: :relationships accepts_nested_attributes_for :parents accepts_nested_attributes_for :relationships, allow_destroy: true end class Parent &lt; ActiveRecord::Base has_many :relationships has_many :children, through: :relationships end class Relationship &lt; ActiveRecord::Base belongs_to :child belongs_to :parent accepts_nested_attributes_for :parents #has :schedule attribute end </code></pre> <p>I would like to set the <code>schedule</code> attribute in Relationships at the same time and can't use <code>accepts_nested_attributes_for</code> as I am manipulating some data in the controller to determine the <code>schedule</code> object before saving.</p> <p>There are many answers on stack overflow for accomplishing this with a pre-existing parent record but I am having trouble finding any for a situation where none of the associations exist previously.</p> <p>I have tried to do this with an <code>after_create</code> callback in the model but don't have access to <code>params</code> and have read that it is bad procedure to do so anyway. ( <a href="https://stackoverflow.com/questions/4725185/rails-how-to-pass-params-from-controller-to-after-save-inside-model">Rails How to pass params from controller to after_save inside model</a>).</p> <p>Ideally I would like to set <code>schedule</code> in the same database call that creates the relationship record along with <code>child_id</code> and <code>parent_id</code>.</p> <p>Any help with this would be awesome, thanks</p> <p><strong>UPDATE</strong></p> <p>Controller as of original post</p> <pre><code>def new @child = Child.new end def create @child = Child.new(params[:child]) schedule = build_schedule(params) # Need to save schedule to @child.relationship[0].schedule somehow if @child.save! redirect_to admins_path else render 'new' end end private def build_schedule(params) # works with params[:mon, :tue, :wed, :thu, :fri] to return a schedule object. end </code></pre> <p>The <code>parent</code> is built using <a href="http://railscasts.com/episodes/196-nested-model-form-revised?view=comments" rel="nofollow noreferrer">Ryan Bates' nested form helper</a>. This is the build line from it:</p> <pre><code>module ApplicationHelper def link_to_add_fields(name, f, association) new_object = f.object.send(association).klass.new ... end end </code></pre> <p>I am not building the <code>relationship</code> at all, it is magically built by rails as far as i'm aware.</p> <p>Trying <strong>Danny Van Hoof's</strong> suggestion <code>@child.relationships[0].schedule =</code> i get <code>undefined method schedule=' for nil:NilClass</code> as no relationship exists.</p> <p>If i build the relationship beforehand either in <code>new</code> or <code>create</code> action using <code>@child.relationship.build</code> I get 2 relationship records being saved:</p> <p><img src="https://i.imgur.com/446q51J.png" alt="relationships table"></p> <p>The one that I built has <code>schedule</code> saved but has no <code>parent_id</code> (parental_group_id) The second record is the one build magically and has both correct ids but no <code>schedule</code>.</p> <p>Now when trying <strong>Rick Peck's</strong> suggestion by adding</p> <pre><code>def params params.require(:child).permit(relationships_attributes: [:schedule]) # tried with and without `parents_attributes` end </code></pre> <p>I get a <code>stack level too deep</code> error on the <code>params.require</code> line. I also don't fully understand what this does. (I'm fairly new to rails)</p> <p>Thanks for helping!</p>
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