Laravel 5 Eloquent Relationship - Has Many Though - eloquent

Question

I have three models.
Study
Site
Unit
Study Has and belongs to many Sites and each site that belongs to Study again has and belongs to many Unit. Please see the following drawing.
http://tinypic.com/r/ojhx0g/8
How I achieve this using Laravel 5 Eloquent Relationships.

Answer 1

It sounds like you have many-to-many relationships between Study->Site and Site->Unit. You can read the Laravel documentation about many-to-many relationships here.
Models
Here are the relevant functions you'll need for Eloquent to recognize the relationships.
class Study extends Model {
// If you named your table differently (like 'studies'), specify that here
protected $table = 'studys';
// This assumes a pivot table named 'site_study', if you named yours
// differently you can pass in into the belongsToMany() function as the
// second parameter.
public function sites() {
return $this->belongsToMany('App\Site');
}
}
class Site extends Model {
protected $table = 'sites';
public function studies() {
return $this->belongsToMany('App\Study');
}
public function units() {
return $this->belongsToMany('App\Unit');
}
}
class Unit extends Model {
protected $table = 'units';
public function sites() {
return $this->belongsToMany('App\Site');
}
}
Then, to access the Sites belonging to a Study you would do this:
$sites = Study::find(1)->sites;
Pivot Table Migrations
Laravel expects pivot tables to be named like 'alpha_beta' where alpha and beta are the singular model names in alphabetical order. So your migrations for the pivot tables would look like this:
class CreateSiteStudyTable extends Migration {
public function up() {
Schema::create('site_study', function(Blueprint $table)) {
$table->integer('site_id')->unsigned();
$table->foreign('site_id')->references('id')->on('sites');
$table->integer('study_id')->unsigned();
$table->foreign('study_id')->references('id')->on('studys'); // or whatever you named it
$table->unique(['site_id', 'study_id']);
$table->timestamps();
});
}
public function down() {
Schema::drop('site_study');
}
}
class CreateSiteUnitTable extends Migration {
public function up() {
Schema::create('site_unit', function(Blueprint $table)) {
$table->integer('site_id')->unsigned();
$table->foreign('site_id')->references('id')->on('sites');
$table->integer('unit_id')->unsigned();
$table->foreign('unit_id')->references('id')->on('units');
$table->unique(['site_id', 'unit_id']);
$table->timestamps();
});
}
public function down() {
Schema::drop('site_unit');
}
}
You can read about Foreign Keys in Laravel here.

Answer 2

you have to create 3 models study, site and unit as per you diagram study has many sites and sites has many units, in you diagram study don't have direct relation with units your eloquent models will be like this.
class Study extends Model {
public function sites(){
return $this->hasMany('App\Site');
}
}
class Site extends Model {
public function units(){
return $this->hasMany('App\Unit');
}
public function study(){
return $this->belongsTo('App\Study');
}
}
class Unit extends Model {
public function sites(){
return $this->belongsTo('App\Site');
}
}