Laravel：团队与比赛之间的关系

Question

I'm currently making a small website where volley-ball Teams will play some Matches . Here is what I have for now:

Match model:

class Match extends Model
{
    public function Team1() {
        return $this->belongsTo('App\Team', 'team_1');
    }

    public function Team2() {
        return $this->belongsTo('App\Team', 'team_2');
    }
}

For example, $match->team1->name works well.

Team model:

class Team extends Model
{
    public $timestamps = false;

    public function Matches() {
        return $this->hasMany('App\Match');
    }
}

But $team->matches gives this error:

SQLSTATE[42S22]: Column not found: 1054 Unknown column 'matches.team_id' in 'where clause'

Which is normal because Laravel tries to find a team_id field in database but there's actually two: team_1 and team_2 .

I'm thinking that relationships between my models might be wrong but I'm not sure.

Thanks for your help !

Answer 1

You are using the right relationship for the data structure you have, but there are two possible ways a team can have a match.

class Team extends Model
{
    public function matchesAsTeam1()
    {
        return $this->hasMany('App\Match', 'team_1');
    }

    public function matchesAsTeam2()
    {
        return $this->hasMany('App\Match', 'team_2');
    }
}

To get all matches in a single relation is slightly tricky, and requires knowing about the ->union() method.

public function matches()
{
    return $this->matchesAsTeam1()->union($this->matchesAsTeam2());
}

This will get all matches where the team is either team 1 or team 2 of the match.

Unfortunately, this doesn't work with eager loading. For example

App\Team::with('matches')->get();

will work to get the matches where that team is team_1 but not the matches where that team is team_2 . If you find yourself using these relations in the context of ->with('matches') , ->has('matches') , and ->whereHas('matches', function($subquery) {}) , this approach will prove problematic in my experience.

I might consider using a many-to-many relationship here, despite the fact that "many" in the second case is always 2. That would involve defining a match_team table:

Schema::create('match_team', function($table) 
{
    $table->increments('id');
    $table->integer('team_id')->unsigned();
    $table->foreign('team_id')->references('id')->on('teams');
    $table->integer('match_id')->unsigned();
    $table->foreign('match_id')->references('id')->on('matches');
});

Then your relations end up being

class Team extends Model
{
    public function matches()
    {
        return $this->belongsToMany(Match::class);
    }
}

class Match extends Model
{
    public function teams()
    {
        return $this->belongsToMany(Team::class);
    }
}

If you do use that approach, you'll need to ensure that you enforce that each match has exactly 2 teams.