Select2 rails form repopulation - ruby-on-rails

Question

I created a rails (v5) form with multiple select and collection_select elements.
Then I use Select2-rails (v4.0.3) to allow a nice selection looking like tags.
The search-options are pulled by ajax.
It works fine until one presses the submit-button with missing required fields.
Valid field-content has now been deleted from the field.
Let me give some example-code:
controller:
...
def form
if params[:form_request].nil?
#form_request = FormRequest.new
else
#form_request = FormRequest.new(params[:form_request])
end
end
def request_form
#form_request = FormRequest.new(params[:form_request])
if #form_request.valid?
render :summary
else
render :form
end
end
...
form:
...
<%= bootstrap_form_for(#form_request, url: '/form/request_form') do |f| %>
<%= f.select :field, [], {label: 'Field label'} %>
<%= f.submit "Submit form" %>
<% end %>
:field is for sure a writable field in the model (and data is set fine)
coffee-script:
Query ->
$("#form_request_from").select2({
ajax: {
url: func =(params) ->
filter = params.term
return "/data.json?filter=" + filter;
,
dataType: 'json',
processResults: processData
},
theme: 'bootstrap',
placeholder: 'Enter data here'
});
processData = (data) ->
mapdata = $.map(data, func =(obj) ->
obj.id = obj.id;
obj.text = obj.name;
return obj;
);
return { results: mapdata };
I am thinking of a lot of possibilities, but at the end I am not sure where the field-data comes from. It is inside the object, but it isn't written to the resulting HTML in any way.
And even if the id would be written as a selected option,
the select2 script would need to know how to transform that into the string to show the real data.
Any idea how to achieve that the data is still written into a field after a failing validation?

Answer 1

After trying out some things I found out how to do it.
At first I just changed the empty array to be the :field variable,too.
This doesn't work too well because it only remembers the ID of the value that has been entered before and like this the SELECT2-script could not find the value to that key and nothing is shown.
Then I created a new variable inside the controller in which I place the array with name and id:
field_object = ObjectsModel.find(#form_request.field.to_i)
#form_field = []
if !field_object.nil?
#form_field = [[field_object.name, field_object.id]]
end
And in the view I now use this field to show the available options:
<%= bootstrap_form_for(#form_request, url: '/form/request_form') do |f| %>
<%= f.select :field, #form_field, {label: 'Field label'} %>
<%= f.submit "Submit form" %>
<% end %>
This works perfectly fine for me without the need to touch the SELECT2-script.
The possible values are still fetched by AJAX but already filled out fields will persist upon redirect to another action.