Retrieving distinct relationships of relationships using Eloquent in Laravel - php

Question

Lets assume I have a model for: Race, Participant, Team
And these relations: Race 1-N Participant N-1 Team
See in another way :
races 1 - N participants
teams 1 - N participants
In Laravel terms:
/* Inside Race model */
public function participants()
{
return $this->hasMany(Participant::class);
}
/* Inside Team model */
public function participants()
{
return $this->hasMany(Participant::class);
}
/* Inside Participant model */
public function race()
{
return $this->belongsTo(Race::class);
}
public function team()
{
return $this->belongsTo(Team::class);
}
In the participants table, It looks like this:
id | team_id | race_id | [a lot of other columns...]
------------------------------
1 | 1 | 1 |
2 | 1 | 1 |
3 | 2 | 1 |
4 | 2 | 1 |
In the above example, I know that the race ID 1 has 2 teams.
I can count them by doing this:
$race = Race::find(1);
$number = $race->participants()->distinct()->count('team_id');
The problem
Counting the number of teams is cool, but I want to access to the list of corresponding Team model instances, so that I can use them for further operations (within a foreach loop for example).
I tried a lot of things without success.
Something like this:
$teams = $race->participants()->distinct()->[...] // Don't know what to put here
The working equivalent SQL query is:
SELECT teams.* FROM teams
INNER JOIN participants ON participants.team_id = teams.id
INNER JOIN races ON races.id = participants.race_id
WHERE races.id = 1
GROUP BY teams.id
Resulting in this:
When the participants table contains this:
I want to know if I can do it with Eloquent instead of using Query/Builder DB:: methods directly ?
EDIT 1
My closest result:
$race->participants()->distinct()->get('team_id')
And then using this list of team_id I can access to the teams using Team::find([list of IDs]) but it looks greedy to me.
EDIT 2
I forgot some information:
The participants.team_id column is NULLABLE because:
There are races with teams of participants
There are races with participants (without team)

Answer 1

I don't think you can easily access to it through the $race instance.
But, you can use the whereHas method on the Team model:
$race = Race::find(1);
$teams = Team::whereHas('participants', function ($query) use ($race) {
$query->where('race_id', $race->id);
})->get(); // ->count() also works
See documentation

Answer 2

To get distinct teams from a race model, you could add a many to many relationship between Race and Team with Participant acting as the pivot.
For example,
/* Race */
public function teams()
{
return $this->belongsToMany(Team::class, 'participants', 'race_id', 'team_id');
}
/* Team */
public function races()
{
return $this->belongsToMany(Race::class,'participants', 'team_id', 'race_id');
}
Then, you could just do this
$race = Race::find($id);
$teams = $race->teams()->distinct()->get();
to get a list of distinct teams for the race.
And since we set up the relationship on both models, you can now also get distinct races for each team by doing
$team = Team::find($id);
$teams = $team->races()->distinct()->get();

Answer 3

First, let's improve your eloquent relations.
// Race
public function teams()
{
return $this->hasMany(Team::class);
}
public function withoutTeamParticipants() // change name that suits you
{
return $this->hasMany(Participant::class);
}
// Team
public function participants()
{
return $this->hasMany(Participant::class); // In this case make sure that participant.race_id is null
}
// Participant
public function team()
{
return $this->belongsTo(Team::class); // When no team, then participant.team_id is null
}
public function race()
{
return $this->belongsTo(Race::class);
}
To access list of participants of a given race:
$race = Race::where('id', 1)->with('teams.participants', 'withoutTeamParticipants')->get();
In your blade you can further use this as:
// List of participants without a team
#foreach ($race->withoutTeamParticipants as $participant)
{{ $participant->name }}
#endforeach
// List of participants that are with a team
#foreach ($race->teams as $team)
#foreach ($team->participants as $participant)
{{ $participant->name }}
#endforeach
#endforeach

Answer 4

You can directly use hasManyThrough relationship inside Race model for fetching distinct teams associated with the race.
public function distinctTeams()
{
return $this->hasManyThrough(Team::class, Participant::class, 'race_id', 'id', 'id', 'team_id')->distinct();
}
Now, you can loop over the teams of a race by using $race->distinctTeams
Hopefully this helps.