Subform columns inheritance proposal

[clyfe]

The subform columns usually inherit from update, when present, or core, as can be seen in the code:

def columns
  # we want to delay initializing to the @core.update.columns set for as long as possible. but we have to eventually clone, or else have a configuration "leak"
  unless @columns
    if @core.actions.include? :update
      @columns = @core.update.columns.clone
    else
      self.columns = @core.columns._inheritable
    end
  end

  @columns
end

They can also be configured by themselves, in controller, like so:

conf.subform.columns = [:col1, col2, ...]

All these behaviors result in having the exact same subform in both create/update situations.

I say a better behavior is to inherit columns from the create action when we deal with a new record or inherit from update action when we deal with an existing record.

Even better, we could have something like:
conf.subform.create that inherits from conf.create and
conf.subform.update inheriting from conf.update.

Here is an example gist that does such a customization: https://gist.github.com/1256348
Relevant parts are:

# _horizontal_subform_header.html.erb
config = active_scaffold_config_for(record.class)
columns = @record.new_record? ? config.create.columns : config.update.columns
columns.each :for => record.class, :crud_type => crud_type, :flatten => true do |column|
...

# _horizontal_subform_record.html.erb
columns = @record.new_record? ? config.create.columns : config.update.columns %>
columns.each :for => @record.class, :crud_type => crud_type, :flatten => true do |column| %>
...

If core members agree I could try and implement something like this.

[scambra]

When do you think create and update columns should be used?

When you are creating a record, all subforms record will be new, but when you are updating a record you will have existing children records in subforms and you will be able to add new records, your example code will use different columns for existing records and new records, so header will be wrong.

[clyfe]

The parent's state new/saved is irrelevant.

If the child is new use conf.subform.create
If it's saved use conf.subform.update

[scambra]

Problem is not parent, but when you are updating the parent you will have children saved children and then you will add new children. If create and update columns are different children which you add have columns under wrong headers, also they could more or less columns than saved children. It doesn't work in horizontal subform, which is a table and all children share the headers.

[clyfe]

Oh, I understand.

1. For singular associations this would not be an issue
2. For plural associations, in case the user configures different arity/order of subform.create & subform.update, default to vertical layout

[scambra]

Ok, I like that, I would merge a pull requests like that, with conf.subform.create_columns and conf.subform.update_columns methods
Also, conf.subform.columns should set both columns sets