Styjun

I have a field call query_data defined as text in my MySQL database.

In my model I defined this field as serialize :query_data, JSON.

The JSON format I would like to save and retrieve look like that:

:items => [
 :id => 1,
 :id => 2,
 :id => 3
]

I have a collection (in that case, called items) that contain an array of objects.

I was wondering, what's the best way to add or delete an Item.

Ex: remove :id => 2 from my items list and add `:id => 4 to it

Ruby on Rails has some nice methods to move seamlessly between JSON and Ruby.

thing = :items => [
 :id => 1,
 :id => 2,
 :id => 3
]
thing.to_json # ""items":["id":1,"id":2,"id":3]"

thing.to_json is essentially what's happening in the serializer. If you want them back to Ruby, you can just do:

@items = @thing.query_data
JSON.parse(@items) # "items"=>["id"=>1, "id"=>2, "id"=>3]}

Now that we can easily move between the two, lets just use Ruby syntax to deal with adding and deleting keys.

thing = :items => [
 :id => 1,
 :id => 2,
 :id => 3
]
thing[:items] = thing[:items].append(:id => 4) # adding a new item
thing[:items] = thing[:items].select # removing an item

First: The second argument to serialize should be the class of object you're storing in the field. You should have serialize :query_data, Hash instead.

Besides that, there aren't really any established best practices for working with serialized data. It really just depends too much on the structure of your data. You might as well ask, "what's the best way to add or delete an item from a hash?"

But since this is a hash you should make sure to keep dirty attributes in mind. If you were to do something like:

items = my_model.query_data[:items]
items.reject! item
items += id: 4

then the model wouldn't know that query_data changed and should be updated on save.

my_model.changed?
# => false
my_model.save
# Won't actually save changes to db.

To avoid this, you can:

A) Make sure you only ever set my_model.query_data directly

B) Explicitly call my_model.query_data_will_change! after changing that field so that it will be properly updated on save.

Base on @veridian-dynamics (thanks for your help!) Here what I did.

Model:

class MyModel < ApplicationRecord
 serialize :item_data, JSON
end

Controller:

class ItemController < ApplicationController
 before_action :authenticate_user!

 def add_item
 begin

 mymodel = MyModel.find_or_create_by(id: param[:model_id])

 if mymodel .item_data.blank?
 item = :items => []
 else
 item = mymodel.item_data.deep_symbolize_keys
 end

 bookmark_exist = item[:items].any? i
 if !bookmark_exist
 item[:items] = item[:items ].append(id: params[:id]) # adding a new item
 end

 mymodel.item_data = item
 mymodel.save

 return render :json => item, :status=> 200 

 rescue Exception => e
 return render :json =>:errors=>e.message, :status=> 400
 puts "ERROR: #e.message"
 end
 end

 def delete_item
 begin

 mymodel = MyModel.find_by(id: params[:model_id])
 if mymodel.present? && mymodel.item_data.present?
 item = mymodel.item_data.deep_symbolize_keys

 item[:items] = (item[:items].select itm) # remove an item
 mymodel.item_data = item 
 mymodel.save

 return render :json => item, :status=> 200 
 end
 rescue Exception => e
 return render :json =>:errors=>e.message, :status=> 400
 puts "ERROR: #e.message"
 end
 end

end