class ActiveRecord::Associations::JoinDependency::Aliases

def column_alias(node, column)
  @alias_cache[node][column]
end

def column_aliases(node)
  @columns_cache[node]
end

def columns
  @tables.flat_map(&:column_aliases)
end

def initialize(tables)
  @tables = tables
  @alias_cache = tables.each_with_object({}) { |table, h|
    h[table.node] = table.columns.each_with_object({}) { |column, i|
      i[column.name] = column.alias
    }
  }
  @columns_cache = tables.each_with_object({}) { |table, h|
    h[table.node] = table.columns
  }
end