Many to many relationship from different column other than id in Laravel

Question

I'm having two models Project and StartYear I'm having a project_technical_details table which holds most of the project information. So I've following table structure in project_technical_details :

project_id    construction_start    construction_area   floors .....

When we were developing we were storing construction_start as year. ie it was hard coded for ex 2012 , 2013 , 2019 etc... Now we want to establish a relationship by which we can manipulate data, so we created a model StartYear and we have following table structure:

id   year  created_at   updated_at

so in this model I defined relationship as:

public function projects()
{
    return $this->belongsToMany(
        'App\Project', 'project_technical_details', 'construction_start', 'project_id');
}

But in this case I want to relate with year column not with the id . How can I achieve it. Thanks.

Answer 1

Your pivot table should look like this:

|------------------------|
| year | project_id | ...|
|------------------------|

Then, in your StartYear model:

public function projects()
{
    return $this->belongsToMany(
        'App\Project', 'project_techinical_details', 'project_id', 'year'
    )
        ->whereColumn('project_techinical_details.construction_start', 'start_year.year');
}

Hope it helps.