Depth Merge

Merge is rather useful, but it has the limitation of staying shallow. Here is a simple extension of an implemented depth merge, with one caveat. Passing in true to delete_nils will remove the key if the value is nil.

Install as a Rails plugin:

./script/plugin install http://source.elevatorfight.com/public/merge_extensions

To gut out the meat just grab this file

An example of use:

# Without trimming nils
hash1 = { :a => "foo", :b => { :c => "bar"} }
hash2 = { :b => { :c => "blah"} }
hash1.depth_merge(hash2) #=> { :a => "foo", :b => { :c => "blah"} }

# With trimming nils
hash1 = { :a => "foo", :b => { :c => "bar"} }
hash2 = { :b => nil }
hash1.depth_merge(hash2, true) #=> { :a => "foo" }

Again a very simple utility, however it comes in handy with testing.

# In Model
class Foo < ActiveRecord::Base
  validates_presence_of :col1, :col2
end

# In Unit Test
...
def setup
  @default_attributes = { :col1 => "foo", :col2 => "bar" }
end

def test_missing_important_fields
  # A model with not only col1 == nil, but nil is never passed to the setter
  model = create_model(:col1 => nil)
  # do some checking on validity

  model = create_model(:col2 => nil)
  # again checking on validity
end

def test_something_else
  model = create_model
end

private
  def create_model(opts = {})
SomeModel.new(@default_attributes.depth_merge(opts, true))
  end
...

Having a the depth part of the merge many not be handy in that scenario, but in functional tests they can help with composing the get/post

# In Functional Test
...
def setup
  ...
  @default_params = {
:id => 5,
:foo => {
  :col1 => "foo",
  :col2 => "bar"
}
  }
end

def test_something
  post :some_action, params(:foo => { :col1 => nil })
  ...
end

def test_something_else
  post :some_action, params
  ...
end

private
  def params(opts = {})
@default_params.depth_merge(opts, true)
  end
...

The premise for this is so tests become more concise, leaving only relevant information. Which in turn make the tests more readable.

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