$http service adding unwanted JSON key to request data - ruby-on-rails

Question

I have a simple service which I'm using to POST data to a Rails controller.
My service looks something like this:
app.service('autoRulesService', function($http) {
return({
createRule: createRule
});
function createRule() {
var request = $http({
method: 'POST',
url: '/rules.json',
data: { one: 'two }
});
return request.then(handleSuccess, handleError);
}
function handleSuccess() {
// body omitted...
}
function handleError() {
// body omitted...
}
});
I use that service in my controller in a pretty standard way:
$scope.saveRule = function() {
rulesService.createRule().then(function() {
// do stuff...
});
}
The problem is that I get a weird unwanted key in my parameters when I inspect the sent data in the Rails log. Where is the "rule" parameter coming from?
Processing by AutoAnalysis::RulesController#create as JSON
Parameters: {"one"=>"two", "rule"=>{}}
It doesn't appear in the request payload (as inspected in Chrome Dev tools)
and my controller action is pretty standard (there's no before filters either):
class RulesController < ApplicationController
def create
# NOTE: I'm referencing an :auto_analysis_rule parameter here because
# that's my desired param key name. It doesn't exist in the request
# as shown here.
render json: Rule.create(params[:auto_analysis_rule])
end
end
and I can't find any mention of $http inferring a root JSON key from the URL or anything in the docs.
Where is the "rule" param key coming from?

Answer 1

Rails automatically wraps parameters that are attributes of the model. If one were an attribute of the Rule model, the payload would look like: {"rule" => {"one" => "two"}}
This functionality removes the need for a top-level key that contains all attributes. In other words, the following payloads would be treated the same if attr1 and attr2 are fields in the MyModel model:
{ "mymodel" : { "attr1" : "val1", "attr2" : "val2" } }
{ "attr1" : "val1", "attr2" : "val2" }
This functionality can be disabled per-controller or app-wide in an initializer. Check out this answer for more information: Rails 3 params unwanted wrapping