Rails view handler for easily generating JSON from view templates
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JSON Rails Templates

This gem allows you to write simple Rails views for JSON output.

When you want JSON output, you normally just define as_json on each model, and respond_with the object. But sometimes you want the same model to display differently from different controllers. In that case, you have a few options:

  1. Don't use the default respond_to.

    You'd use specialized as_json methods, and have each controller call the appropriate specialized method. We went through this, and it did not work so well. We ended up with a lot of different as_json methods. It felt like we were doing too much work in the models that did not feel like it belonged there.

  2. Use a presenter class.

    We tried this as well, and it felt too heavy-handed. We ended up with lots of classes that didn't seem to be doing much.

    We're considering trying a variant of this called [DCI]http://en.wikipedia.org/wiki/Data,_Context,_and_Interaction. The idea is that the model contains only data, and when we need some behavior from the object, we inject a module into the object with the behavior only for that specific context. So each view would be considered a different context, with an as_json appropriate for that context.

  3. Use a JSON view file.

    This seems the simplest, and fits in pretty well with the way Rails works, especially with HTML. It takes the (Rails-ish) perspective that we're just looking at different views of the same model object, and keeps these different views out of the model.

    We tried this with plain ERB, but it didn't work out too well -- we had to jump through some hoops to output raw text.


This template:

string_literal: 'this is a string'
string_expression: 'this is a string'.gsub('string', 'String!')
integer_literal: 123
integer_expression: 1 + 2
float_literal: 1.234
float_expression: Math::PI * 2
boolean_literal: true
boolean_expression: 'Craig' == 'Buchek'
null_literal: nil
array_literal: ['string', 123, 1.234, false]
array_expression: Array.new(3, 'hello')
hash_literal: {a: 1, b: '2', 'c' => 3}
    grandchild: 1

will render JSON equivalent to (ignoring whitespace differences):

  "string_literal": "this is a string",
  "string_expression": "this is a String!",
  "integer_literal": 123,
  "integer_expression": 3,
  "float_literal": 1.234,
  "float_expression": 6.283185307179586,
  "boolean_literal": true,
  "boolean_expression": false,
  "null_literal": null,
  "array_literal": ["string", 123, 1.234, false],
  "array_expression": ["hello", "hello", "hello"],
  "hash_literal": { "a": 1, "b": "2", "c": 3 }
  "nested_contexts": {
    "child": {
      "grandchild": 1


  • Nesting levels are indicated by 2 spaces. Indenting with non-space whitespace characters or an odd number of spaces will raise an exception.


  1. Iterating over an array of objects, specifying how to render each.
  2. Compile templates instead of using eval.
  3. Integrate with tilt.

Implement these translations:

  1. hash expression
  2. object
  3. array of objects
  4. partial
  5. partial with an object
  6. partial with a collection

Consider these ideas:

  1. Allow a toggle to omit nil/null from being included in output.
    • Could use a sigil when you really do want to include a nil/null: VisibleNull(nil)
  2. Allow (or require) commas at end of each line.
  3. Use as_json where available for objects when there is no partial.
  4. Translate dates/times to strings automatically.
  5. Generate an error when encountering a date/time expression.
  6. Generate an error when encountering an object with no partial or as_json.
    • May try to_json or to_hash as well.
  7. Require or allow {} or [] around the top-level content.
  8. Allow specifying a context, so we can just do attribute on the right side everywhere instead of resource.attribute.
    • Probably use a syntax like =object_or_hash.
  9. Override render() to return hashes and arrays instead of a string.


JSON Rails Templates was originally written by Craig Buchek.

Ideas were contributed by Amos King.

The impetus for creating this gem came from experience working on a project along with Matt Simpson, Helena Wotring, and Nick Bimpasis.


Copyright © 2011 by BoochTek, LLC. Copyright © 2012 by Asynchrony Solutions, LLC.

Released under the MIT license.