laravel advanced join on 5 tables, with 2 tables campared - mysql

Question

I'm not even sure this is possible, I can get it to work up to the 2nd join function, then it just return null.
$articles = DB::table('courses')
->join('version','courses.current_version_id','=','version.id')
->join('category as c1', function($join1){
$join1->on('courses.code','=','c1.title');
})
->join('category as c2', function($join2){
$join2->on('version.version_number','=','c2.title');
})
->join('articleCategories','c2.id','=','articleCategories.cat_id')
->join('articles','articleCategories.article_id','=','articles.id')
->where('c2.parent_id','=','c1.id')
->where('courses.id','=',$course)
->select('courses.code','courses.title','version.version_number','articles.*')
->get();
Is this even possible? What am I getting wrong?

Answer 1

You may try something like this:
$fieldsToSelect = array(
'courses.code',
'courses.title',
'courses.current_version_id',
'version.version_number',
'version.id',
'category.id',
'category.title',
'articleCategories.cat_id',
'articleCategories.article_id',
'articles.*'
);
$articles = DB::table('courses')->join('version', function($join){
$join->on('courses.current_version_id', '=', 'version.id');
})->join('category', function($join) {
$join->on('courses.code', '=', 'category.title')
->on('version.version_number', '=', 'category.title');
})->join('articleCategories', function($join){
$join->on('category.id', '=', 'articleCategories.cat_id');
})->join('articles', function($join){
$join->on('articleCategories.article_id', '=', 'articles.id');
})
->get($fieldsToSelect);