Rails converts empty arrays into nils in params of the request

Question

I have a Backbone model in my app which is not a typical flat object, it's a large nested object and we store the nested parts in TEXT columns in a MySQL database. I wanted to handle the JSON encoding/decoding in Rails API so that from outside it looks like you can POST/GET this one large nested JSON object even if parts of it are stored as stringified JSON text. However, I ran into an issue where Rails magically converts empty arrays to `nil` values. For example, if I POST this: ``` { name: "foo", surname: "bar", nested_json: { complicated: [] } } ``` My Rails controller sees this: ``` { :name => "foo", :surname => "bar", :nested_json => { :complicated => nil } } ``` And so my JSON data has been altered.. Has anyone run into this issue before? Why would Rails be modifying my POST data? UPDATE Here is where they do it: https://github.com/rails/rails/blob/master/actionpack/lib/action_dispatch/http/request.rb#L288 And here is ~why they do it: https://github.com/rails/rails/pull/8862 So…

Accepted Answer

After much searching, I discovered that you starting in Rails 4.1 you can skip the deep_munge "feature" completely using

```
config.action_dispatch.perform_deep_munge = false
```

I could not find any documentation, but you can view the introduction of this option here: https://github.com/rails/rails/commit/e8572cf2f94872d81e7145da31d55c6e1b074247

There is a possible security risk in doing so, documented here: https://groups.google.com/forum/#!topic/rubyonrails-security/t1WFuuQyavI

Rails converts empty arrays into nils in params of the request

Solution

Problem