Repacking query result from multiple models. Rails-way - ruby-on-rails

Question

I have a controller that renders json. Here's code:
class AppLaunchDataController < ApiController
def index
service_types = []
vendors = []
tariffs = []
fields = []
vendors_hash = {}
service_types_hash = {}
tariffs_hash = {}
fields_hash = {}
#service_types = ServiceType.select("title, id").all.each do |service_type|
service_types_hash = {id: service_type.id, title: service_type.title}
service_types << service_types_hash
#vendors = service_type.vendors.select("title, id").all.each do |vendor|
vendors_hash = {id: vendor.id, title: vendor.title}
vendors << vendors_hash
#tariff = vendor.tariffs.select("title, id").all.each do |tariff|
tariffs_hash = {id: tariff.id, title: tariff.title}
tariffs << tariffs_hash
#fields = tariff.fields.select("id, current_value, value_list").all.each do |field|
fields_hash = {id: field.id, current_value: field.current_value, value_list: field.value_list}
fields << fields_hash
end
tariffs_hash[:fields] = fields
fields = []
end
vendors_hash[:tariffs] = tariffs
tariffs = []
end
service_types_hash[:vendors] = vendors
vendors = []
end
render json: service_types
end
end
Return value looks like this:
[{"id":1,"title":"Water",
"vendors":[{"id":1,"title":"Vendor_1",
"tariffs":[{"id":1,"title":"Unlim",
"fields":[{"id":1,"current_value":"200","value_list":null},{"id":2,"current_value":"Value_1","value_list":"Value_1, Value_2, Value_3"}]},{"id":2,"title":"Volume",
"fields":[]}]},
{"id":2,"title":"Vendor_2",
"tariffs":[]}]},
{"id":2,"title":"Gas",
"vendors":[]},
{"id":3,"title":"Internet",
"vendors":[]}]
It works, but I'm sure there's another (more rails-) way to get the result.
If anyone dealt with it before, please help. Thanks.

Answer 1

just use
# for eager-loading :
#service_types = ServiceType.includes( vendors: {tariffs: :fields} )
# now for the json :
#service_types.to_json( include: {vendors: {include: {tariffs: { include: :fields}}}} )
if your ServiceType object will always have this kind of representation, just override the model's as_json method:
class ServiceType
def as_json( options={} )
super( {include: :vendors }.merge(options) ) # vendors, etc.
end
end
this is encouraged way to do it in rails : calling to_json on the model will just call as_json, possibly with additional options. In fact, as_json describes the canonical json representation for this model. See the api dock on to_json for more insight.
If your needs are more peculiar ( as using selects for a faster query ), you can always roll your own to_json_for_app_launch_data method on the model (using or not as_json), or even better on a presenter