How can I include only one associated record from a has_many relationship when doing JSON serialization?

rubyonrails-talk
1 
# location_products is a has_many :through relationship between Product and Location.
# when params[:location_id] is specified, I only want the one join table record that matches 
# params[:location_id], rather than all of them, 
# and I would like this included in the JSON output somehow
products = products.includes(:location_products).where('inv_location_products.location_id' => params[:location_id]).distinct if params[:location_id]

include_methods = [:main_image, :primary_vendor]
# :location_products is a has_many relationship, when passed to as_json
# it will include every LocationProduct.
# I only want the one specified by params[:location_id]
# maybe as_json is not so flexible?
include_methods << [:location_products] if params[:location_id]

render json: {
  total_count: products.total_count,
  products: products.as_json(methods: include_methods)
}.to_json
2

(untested)

products = products.includes(:location_products).where(‘inv_location_products.location_id’ => params[:location_id]).distinct if params[:location_id]

include_methods << :location_products[0] if params[:location_id]

render json: { total_count: products.total_count, products: products.as_json(methods: include_methods) }.to_json

Always filter the objects as early as possible in your retrieval. – H

3

Perhaps consider using jBuilder instead of as_json.

as_json has some flexibility but it is fundamentally tied to the model making it nice for quick stuff that is often good enough but sometimes not quite flexible enough. jBuilder OTOH gives you complete control over the JSON document.

You can either use jBuilder as a template that a controller calls or even just use it directly in the model much as as_json.

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