Laravel eloquent limit results - php

Question

I have a working query:
Object::all()->with(['reviews' => function ($query) {
$query->where('approved', 1);
}])
And I want to limit the number of reviews, per object, that is returned. If I use:
Object::all()->with(['reviews' => function ($query) {
$query->where('approved', 1)->take(1);
}])
or
Object::all()->with(['reviews' => function ($query) {
$query->where('approved', 1)->limit(1);
}])
it limits the total number of reviews, where I want to limit the reviews that are returned by each object. How can I achieve this?

Answer 1

Eloquent way
Make one relationship like below in your model class
public function reviews() {
return $this->hasMany( 'Reviews' );
}
//you can pass parameters to make limit dynamic
public function firstReviews() {
return $this->reviews()->limit( 3 );
}
Then call
Object::with('firstReviews')->get();
Faster way(if you just need one review)
Make a derived table to get the latest review 1st and then join it.
Object->select('*')
->leftJoin(DB::raw('(SELECT object_id, reviews FROM reviews WHERE approved=1 ORDER BY id DESC limit 0,1
as TMP'), function ($join) {
$join->on ( 'TMP.object_id', '=', 'object.id' );
})
->get();

Answer 2

Grabbing 1 child per parent
You can create a helper relation to handle this very easily...
In your Object model
public function approvedReview()
{
return $this->hasOne(Review::class)->where('approved', 1);
}
Then you just use that instead of your other relation.
Object::with('approvedReview')->get();
Grabbing n children per parent
If you need more than 1, things start to become quite a bit more complex. I'm adapting the code found at https://softonsofa.com/tweaking-eloquent-relations-how-to-get-n-related-models-per-parent/ for this question and using it in a trait as opposed to a BaseModel.
I created a new folder app/Traits and added a new file to this folder NPerGroup.php
namespace App\Traits;
use DB;
trait NPerGroup
{
public function scopeNPerGroup($query, $group, $n = 10)
{
// queried table
$table = ($this->getTable());
// initialize MySQL variables inline
$query->from( DB::raw("(SELECT #rank:=0, #group:=0) as vars, {$table}") );
// if no columns already selected, let's select *
if ( ! $query->getQuery()->columns)
{
$query->select("{$table}.*");
}
// make sure column aliases are unique
$groupAlias = 'group_'.md5(time());
$rankAlias = 'rank_'.md5(time());
// apply mysql variables
$query->addSelect(DB::raw(
"#rank := IF(#group = {$group}, #rank+1, 1) as {$rankAlias}, #group := {$group} as {$groupAlias}"
));
// make sure first order clause is the group order
$query->getQuery()->orders = (array) $query->getQuery()->orders;
array_unshift($query->getQuery()->orders, ['column' => $group, 'direction' => 'asc']);
// prepare subquery
$subQuery = $query->toSql();
// prepare new main base Query\Builder
$newBase = $this->newQuery()
->from(DB::raw("({$subQuery}) as {$table}"))
->mergeBindings($query->getQuery())
->where($rankAlias, '<=', $n)
->getQuery();
// replace underlying builder to get rid of previous clauses
$query->setQuery($newBase);
}
}
In your Object model, import the trait use App\Traits\NPerGroup; and don't forget to add use NPerGroup right under your class declaration.
Now you'd want to setup a relationship function to use the trait.
public function latestReviews()
{
return $this->hasMany(Review::class)->latest()->nPerGroup('object_id', 3);
}
Now you can use it just like any other relationship and it will load up the 3 latest reviews for each object.
Object::with('latestReviews')->get();