Rails form to create model with reference - ruby-on-rails

Question

I'm trying to create a model form that will allow me to add references by name via a <select> tag.
e.g.
In the database there are already RefModels with ref_name = "a", ref_name = "b", ref_name = "c".
Form:
<%= form_for #model %>
<%= f.label :ref_models, "Referenced Models:" %>
<%= f.select :ref_models, ["a","b","c"], {}, {:multiple => true} %>
Controller:
def create
#model = Model.new(model_params)
params[:model][:ref_models].each do |ref|
#ref = RefModel.where("ref_name = ?", ref)
#model.ref_models << #ref
end
respond_to do |format|
...
end
end
In my logs I'm getting this error:
Started POST "/models" for 127.0.0.1 at 2013-06-25 16:20:48 -0300
Processing by ModelssController#create as JS
Parameters: {"utf8"=>"✓", "models"=>{..., "ref_models"=>["a", "b", "c"], ...}, "commit"=>"Create"}
Completed 500 Internal Server Error in 2ms
ActiveRecord::AssociationTypeMismatch (RefModel(#70144007274440) expected, got String(#70144005442620)):
app/controllers/models_controller.rb:52:in `create'
What's the problem?
Note:
I changed the actual model names for "model" and "ref_model" to generalize.
EDIT:
The error occurs on this line:
#model = Model.new(model_params)

Answer 1

The error comes from this part:
#model = Model.new(model_params)
I'm pretty sure your model_params is actually params[:model]. If yes, it means it tries to create a record for Model with the attribute ref_models and the values contained in params[:model][:ref_models]
You should take off the params[:model][:ref_models] before passing it to the Model.new(params[:model]):
def create
ref_models = params[:model].delete(:ref_models)
#model = Model.new(params[:model])
ref_models.each do |ref|
#ref = RefModel.where("ref_name = ?", ref)
#model.ref_models << #ref
end
respond_to do |format|
...
end
end

Answer 2

Do these ref_models have IDs as well as names? If so, you can get Rails to do the heavy lifting for you.
In your view, do:
<%= f.select :ref_model_ids, RefModel.all.collect {|x| [x.name, x.id]}, {}, :multiple => true %>
Then, you can take out the custom code from your controller, Rails knows how to link those models up appropriately. That's assuming you have a table like model_ref_model with columns for model_id and ref_model_id.
Hope that helps...