Laravel 5.3 - HasMany关系不能使用Join语句

Question

I am trying to retrieve symbols with their comments using hasMany in laravel 5.3

Symbol.php

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

Comment.php

public function symbol() {
    return $this->belongsTo('App\Symbol');
}

---

when I run:

$symbols = Symbol::with('comments')->paginate(100);

I get the correct output (lists all symbols with their comments)

@foreach ($symbols as $s)
    {{ $s->name }}
    @foreach ($s->comments as $c)
         {{ $c->body }}
    @endforeach
@endforeach

but when I add a join to the statement:

$symbols = Symbol::with('comments')
    ->join('ranks', 'symbols.id', '=', 'ranks.symbol_id')
    ->join('prices', 'symbols.id', '=', 'prices.symbol_id')
    ->paginate(100);

The foreach loop has no comments for every symbol. Any idea why the join would be causing this?

Answer 1

When you are doing joins like this, attributes with the same names will be overwritten if not selected. So select the attributes you need for your code, and nothing else. As shown below.

$symbols = Symbol::with('comments')
    ->join('ranks', 'symbols.id', '=', 'ranks.symbol_id')
    ->join('prices', 'symbols.id', '=', 'prices.symbol_id')
    ->select('symbols.*', 'ranks.importantAttribute', 'prices.importantAttribute')
    ->paginate(100);

Basicly i think your ids are being overwritten, by the two joins because they also have id fields, i have had a similar problem doing joins, and it breaks relations if the id is overwritten.

And you have to be carefull, all fields who shares names can be overwritten and parsed wrong into the models.