Module: Rhubarb::FindFreshest

Included in:
PersistingClassMixins
Defined in:
lib/rhubarb/mixins/freshness.rb

Instance Method Summary collapse

Instance Method Details

#find_freshest(args) ⇒ Object

args contains the following keys

* :group_by maps to a list of columns to group by (mandatory)
* :select_by maps to a hash mapping from column symbols to values (optional)
* :version maps to some version to be considered "current" for the purposes of this query; that is, all rows later than the "current" version will be disregarded (optional, defaults to latest version)



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# File 'lib/rhubarb/mixins/freshness.rb', line 19

def find_freshest(args)
  args = args.dup

  args[:version] ||= Util::timestamp
  args[:select_by] ||= {}

  query_params = {}
  query_params[:version] = args[:version]

  select_clauses = ["created <= :version"]

  valid_cols = self.colnames.intersection args[:select_by].keys

  valid_cols.map do |col|
    select_clauses << "#{col.to_s} = #{col.inspect}"
    val = args[:select_by][col]
    val = val.row_id if val.respond_to? :row_id
    query_params[col] = val
  end

  group_by_clause = "GROUP BY " + args[:group_by].join(", ")
  where_clause = "WHERE " + select_clauses.join(" AND ")
  projection = self.colnames - [:created]
  join_criteria = projection.map do |column|
    "__fresh.#{column} = __freshest.#{column}"
  end

  projection << "MAX(created) AS __current_version"
  join_criteria << "__fresh.__current_version = __freshest.created"

  join_clause = join_criteria.join(' AND ')
  
  query = "
  SELECT __freshest.* FROM (
SELECT #{projection.to_a.join(', ')} FROM (
  SELECT * from #{quoted_table_name} #{where_clause}
) #{group_by_clause}
  ) as __fresh INNER JOIN #{quoted_table_name} as __freshest ON #{join_clause} ORDER BY row_id"
  self.db.execute(query, query_params).map {|tup| self.new(tup) }
end