Support for default attributes for JSON columns

Problem this feature will solve

Currently, I can create a factory like this:

FactoryBot.define do
  factory :a do
    my_json_column do
      {
        "a" => 1,
        "b" => 2,
        "c" => 3,
      }
    end
  end
end

and use it like this:

create :a, my_json_column: { "a" => 2, "b" => 3, "c" => 4 }

which means I have to specify every key which I want to appear in my_json_column.

Desired solution

I'm wondering if it would be possible to do something like this:

FactoryBot.define do
  factory :a do
    json :my_json_column do # or maybe hash? or json_factory?
      {
        "a" => 1,
        "b" => 2,
        "c" => 3,
      }
    end
  end
end

which would mean that I could only pass in the properties I cared about, and the rest would just be populated from the definition in the factory (similar to regular properties in factory).

a = create :a, my_json_column: { "a" => 2 }
a.my_json_column # { "a" => 2, "b" => 2, "c" => 3 }

Alternatives considered

I've considered doing something like this (or similar) as a workaround, though it doesn't seem that clean, especially if you are doing it a fair bit.

atrs = attributes_for :a
create :a, my_json_column: { **atrs.my_json_column, "a" => 2 }

But if anyone has any other suggestions then I'm all ears!

Additional context

Example use case:

Imagine you have a config json column, which just stores some flexible key-value pairs for a model; if you have some sort of validation on this, which checks for various keys, it would be cumbersome to specify all of them every time you have a test which just tests a single one of those keys.

Thanks!

Start by reading the factory definition and the create and attributes_for entry points described in the issue. Check how JSON-column values are currently assigned, then define and test an API for defaults. Done means callers can override selected keys while unspecified keys retain the factory defaults.