I am using the Data Mapper Pattern and I am wondering what is the best way to handle relationships with that pattern. I spent a lot of time searching for solutions in Google and Stack overflow, I found some but I am still not completely happy about them, especially in one special case that I will try to explain.
I am working with PHP so the examples of code that I will put are in PHP.
Let's say I have a table "team" (id, name) and a table "player" (id, name, team_id). This is a 1-N relationship. By implementing the Data Mapper pattern, we will have the following classes: Team, TeamMapper, Player and PlayerMapper.
So far, everything is simple. What if we want to get all players from a team?
The first solution I found is to create a method getAllPlayers() in the Team class which will handle that with lazy loading and proxies. Then, we can retrieve the players of a team like that:
$players = $team->getAllPlayers();
The second solution I found is to directly use the PlayerMapper and pass the team ID as parameter. Something like:
$playerMapper->findAll(array('team_id' => $team->getId()));
But now, let's say that I want to display a HTML table with all the teams and with a column 'Players' with all of the players of each team. If we use the first solution I described, we will have to do one SQL query to get the list of teams and one query for each team to get the players, whcih means N+1 SQL queries where N is the number of teams.
If we use the second solutions I described, we can first retrieve all team IDs, put them in an array, and then pass it to the findAll method of the player mapper, something like that:
$playerMapper->findAll(array('team_id' => $teamIds));
In that case, we need to run only 2 queries. Much better. But I am still not very happy with that solution because the relationships are not described