Class: ActiveRecord::Associations::JoinDependency

Inherits:

Object

• Object
• ActiveRecord::Associations::JoinDependency

Defined in:

lib/brick.rb

Instance Method Summary

• #apply_column_aliases(relation) ⇒ Object

  An intelligent .eager_load() and .includes() that creates t0_r0 style aliases only for the columns used in .select().

Instance Method Details

#apply_column_aliases(relation) ⇒ Object

An intelligent .eager_load() and .includes() that creates t0_r0 style aliases only for the columns used in .select(). To enable this behaviour, include the flag :_brick_eager_load as the first entry in your .select(). More information: discuss.rubyonrails.org/t/includes-and-select-for-joined-data/81640

# File 'lib/brick.rb', line 1332

def apply_column_aliases(relation)
  if (sel_vals = relation.select_values.map(&:to_s)).first == '_brick_eager_load'
    used_cols = {}
    # Find and expand out all column names being used in select(...)
    new_select_values = sel_vals.each_with_object([]) do |col, s|
      next if col == '_brick_eager_load'

      if col.include?(' ') # Some expression? (No chance for a simple column reference)
        s << col # Just pass it through
      else
        col = if (col_parts = col.split('.')).length == 1
                [col]
              else
                [col_parts[0..-2].join('.'), col_parts.last]
              end
        used_cols[col] = nil
      end
    end
    if new_select_values.present?
      relation.select_values = new_select_values
    else
      relation.select_values.clear
    end

    @aliases ||= Aliases.new(join_root.each_with_index.map do |join_part, i|
      join_alias = join_part.table&.table_alias || join_part.table_name
      keys = [join_part.base_klass.primary_key] # Always include the primary key

      # # %%% Optional to include all foreign keys:
      # keys.concat(join_part.base_klass.reflect_on_all_associations.select { |a| a.belongs_to? }.map(&:foreign_key))

      # Add foreign keys out to referenced tables that we belongs_to
      join_part.children.each { |child| keys << child.reflection.foreign_key if child.reflection.belongs_to? }

      # Add the foreign key that got us here -- "the train we rode in on" -- if we arrived from
      # a has_many or has_one:
      if join_part.is_a?(ActiveRecord::Associations::JoinDependency::JoinAssociation) &&
         !join_part.reflection.belongs_to?
        keys << join_part.reflection.foreign_key
      end
      keys = keys.compact # In case we're using composite_primary_keys
      j = 0
      columns = join_part.column_names.each_with_object([]) do |column_name, s|
        # Include columns chosen in select(...) as well as the PK and any relevant FKs
        if used_cols.keys.find { |c| (c.length == 1 || c.first == join_alias) && c.last == column_name } ||
           keys.find { |c| c == column_name }
          s << Aliases::Column.new(column_name, "t#{i}_r#{j}")
        end
        j += 1
      end
      Aliases::Table.new(join_part, columns)
    end)
  end

  relation._select!(-> { aliases.columns })
end