# How to overwrite to_json (as_json) in Active Record models in Rails

Let's say you have a model in Rails with certain attributes and columns. When you serialize it with `to_json`, by default Rails will include all columns. How can you add one more or remove some from now appearing there?

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## to_json ? Use as_json instead

In the simplest way you can define the `as_json` method on your model. You can call `super` to get the standard behavior from `ActiveRecord::Base` and then add or remove more attributes on that result.

Imagine that you have `Event` class. And initially the JSON looks like.

```js
{
  "id": 1,
  "title": "Ergonomic Granite Table course",
  "description": "You can’t just skip ahead to where you think...",
  "starts_at": "2017-10-10T00:00:00.000Z",
  "ends_at": "2017-10-13T00:00:00.000Z",
  "category": "Holiday",
  "state": "published",
  "image_url": "http://lorempixel.com/600/338/animals/1",
  "created_at": "2017-10-03T09:30:25.481Z",
  "updated_at": "2017-10-04T08:36:43.049Z",
}
```

You might want to remove `created_at`, `updated_at` and add one new field such as `is_single_day_event`.

You can do it that way:

```ruby
class Event < ApplicationRecord
  def single_day_event?
    starts_at.to_date == ends_at.to_date
  end

  def as_json(*)
    super.except("created_at", "updated_at").tap do |hash|
      hash["is_single_day_event"] = single_day_event?
    end
  end
end
```

And now when you call `event.to_json` you are going to get

```js
{
  "id": 1,
  "title": "Ergonomic Granite Table course",
  "description": "You can’t just skip ahead to where you think...",
  "starts_at": "2017-10-10T00:00:00.000Z",
  "ends_at": "2017-10-13T00:00:00.000Z",
  "category": "Holiday",
  "state": "published",
  "image_url": "http://lorempixel.com/600/338/animals/1",
  "is_single_day_event": true,
}
```

If the logic around serializing your objects gets more complex over time or you need multiple representations of the same model, I suggest you decouple JSON serialization from ActiveRecord. You can do it by using of the gems such as `ActiveModel::Serializers` or similar.

<a href="https://ruby.libhunt.com/categories/24-api-builder" rel="nofollow">Potential gems for you to investigate</a>

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