Laravel Eloquent relationship with more than one join column - laravel

Question

I'm new to laravel and try to use Eloquent.
Assuming there is the following database structure:
CREATE TABLE `a` (
`userid` int(11) NOT NULL,
`aid` int(11) NOT NULL,
`name` varchar(255) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `p` (
`userid` int(11) NOT NULL,
`pid` int(11) NOT NULL,
`aid` int(11) NOT NULL,
`text` text NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
ALTER TABLE `a` ADD PRIMARY KEY (`userid`,`aid`);
ALTER TABLE `p` ADD PRIMARY KEY (`userid`,`pid`);
Now I want a relation between the tables:
p contains a with p.userid=a.userid AND p.aid=a.aid
How can I do a relationship with more than one column?

Answer 1

First I want to mention that if you can't find a straight solution, there is always a workaround. The reason why you cannot do a relationship with more than one column in one table is that you need the same number of columns in the other table. So if you had 2 columns of type int in the first table, you need 2 columns of type int in the second table aswell to link them both. And as I see from what you provided, you are repeating data which suggests that your database is not normalized. I would suggest you do the following:
CREATE TABLE `a` (
`userid` int(11) NOT NULL,
`aid` int(11) NOT NULL unique,
`name` varchar(255) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `p` (
`id` int(11) NOT NULL,
`userid` int(11) NOT NULL,
`pid` int(11) NOT NULL unique,
`text` text NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
ALTER TABLE `a` ADD PRIMARY KEY (`userid`);
ALTER TABLE `p` ADD PRIMARY KEY (`id`);
ALTER TABLE `p` ADD FOREIGN KEY (`userid`) REFERENCES `a` (`userid`)
This is what I think that is more suitable for you. However to answer your question, since you are using laravel in the a model do this:
class A extends Eloquent{
public function p(){
return $this->belongsTo('App\P','userid')
// or hasMany
}
public function p(){
return $this->belongsTo('App\P','aid')
// or hasMany
}
}
and the same thing in the p model
class P extends Eloquent{
public function a(){
return $this->hasMany('App\A','userid')
//or belongsTO
}
public function a(){
return $this->hasMany('App\A','pid')
//or belongsTO
}
}
NOTE
PLEASE keep in mind that the method belongsTo or hasMany is decided by your database model, on how you defined the database.