In Laravel I have ModelA, ModelB and ModelC. ModelA has many ModelB. ModelB has many ModelC. I want to retrieve all ModelC for a selection of ModelA. How do I do this?
I tried the following:
$models = ModelC::with(['modelB','modelB.modelA' => function ($query) {
$query->where('owner', 123);
}])->get();
But the first query in that case is select * from model_c. Obviously not the result I am looking for.
Imagine that you were received 100 objects from the database, and each record had 1 associated model (i.e. belongsTo). Using an ORM would produce 101 queries by default; one query for the original 100 records, and additional query for each record if you accessed the related data on the model object. In pseudo code, let’s say you wanted to list all published authors that have contributed a post. From a collection of posts (each post having one author) you could get a list of author names like so:
$posts = Post::published()->get(); // one query
$authors = array_map(function($post) {
// Produces a query on the author model
return $post->author->name;
}, $posts);
We are not telling the model that we need all the authors, so an individual query happens each time we get the author’s name from the individual Post model instances.
Eager Loading
As I mentioned, ORMs “lazy” load associations. If you intend to use the associated model data you can trim that 101 query total to 2 queries using eager loading. You just need to tell the model what you need it to load eagerly.
Here’s an example from the Rails Active Record guide on using eager loading. As you can see, the concept is quite similar to Laravel’s eager loading concept.
$posts = Post::with('author')->limit(100)->get();
I find that I receive better understanding by exploring ideas from a wider perspective. The Active Record documentation covers some examples that can further help the idea resonate.
I managed to solve this with nested whereHas calls as follows:
$models = modelC::whereHas('modelB', function ($query) {
$query->whereHas('modelA', function ($query) {
$query->where('owner', 123);
});
})->get();
Laravel to the rescue, yet again!
Related
I have various parent/child relationships, drilling down a few levels. What I want to know is if its possible to do something like this:
$student = Student::find(1);
$student->bursaries()->enrolments()->courses()->where('course','LIKE','%B%');
(With the end goal of selecting the course which is like '%B%'), or if I would have to instead use the DB Query builder with joins?
Models / Relationships
Student:
public function bursaries() {
return $this->hasMany('App\StudentBursary');
}
StudentBursary:
public function enrolments() {
return $this->hasMany('App\StudentBursaryEnrolment');
}
If what you want is to query all courses, from all enrollments, from all bursaries, from a students, then, unfortunately, you are one table too many from getting by with the Has Many Through relationship, because it supports only 3 tables.
Online, you'll find packages that you can import / or answers that you can follow to provide you more though of solutions, for example:
1) How to use Laravel's hasManyThrough across 4 tables
2) https://github.com/staudenmeir/eloquent-has-many-deep
Anyhow, bellow's something you can do to achieve that with Laravel alone:
// Eager loads bursaries, enrolments and courses, but, condition only courses.
$student = Student::with(['bursaries.enrolments.courses' => function($query) {
$query->where('course','LIKE','%B%');
}])->find(1);
$enrolments = collect();
foreach($student->bursaries as $bursary) {
$enrolments = $enrolments->merge($bursary->enrolments);
}
$courses = collect();
foreach ($enrolments as $enrolment) {
$courses = $courses->merge($enrolment->courses);
}
When you do $student->bursaries() instead of $student->bursaries, it returns a query builder instead of relationship map. So to go to enrolments() from bursaries() you need to do a bursaries()->get(). It should look like this.
$student->bursaries()->get()[0]->enrolments(), added the [0] because im using get(), you can use first() to avoid the [0]
$student->bursaries()->first()->enrolments()
But I'm not sure if it will suffice your requirement or not.
I already read doc here :
https://github.com/laravel/framework/pull/25997
What i want to know is by using withCount() we were just load count of records instead of getting all relations data.
So by using loadCount() what we can do ?
Please explain in short in simple words.
Thanks
loadCount Eloquent Collection Method introduced by the release of Laravel 5.7.10. According to the laravel-news.
loadCount is the ability to load relationship counts on an Eloquent collection. Before this feature, you could only load relationships, but now you can call loadCount() to get counts for all relations.
The pull request illustrates how you could use loadCount() with the following example:
$events = Event::latest()->with('eventable')->paginate();
$groups = $events->map(function ($event) {
return $event->eventable;
})->groupBy(function ($eventable) {
return get_class($eventable);
});
$groups[Post::class]->loadCount('comments');
$groups[Comment::class]->loadCount('hearts');
return new EventIndexResponse($events);
I am trying to replicate the result set that I get when using Eloquent ORM, except with Laravel Query Builder. Basically using this code I can get the packs to appear nested within the products so that when I loop them on the view I can further loop the packs within each products. Seems pretty basic right (see result set below).
$get_posts_for_product = Product::where('active', 1)
->with('packs')
->get()->toArray();
I have tried a few ways using Query Builder to get this to work but it joins the packs inline as I thought it would.
What is the best way to get this same Array structure using Query Builder, I am aware that the result set is a different type of array and that is fine but for my project it must be done using Query Builder at this point.
Thanks.
I would say, that is why you have Eloquent: you don't have to worry about how to have those relationships together.
However incase you really want to achieve the same result I will demo this using two tables users and messages:
1st method:
Retrieve the users and transform it by querying the database for relationships:
$result = DB::table('users')->get()->transform(function ($user){
$user->messages = DB::table('messages')->where('user_id', $user->id)->get();
return $user;
});
Downside: Having many users means a lot of db query on messages table.
Upside: less codes to write
2nd method:
Retrieve both tables using all the ids of user to query the messages:
$users = DB::table('users')->get();
$messages = DB::table('messages')->whereIn('user_id', $users->pluck('id')->toArray())->get();
$result = $users->transform(function ($user) use ($messages){
$user->messages = $messages->where('user_id', $user->id)->values();
return $user;
});
Downside: The need to still transform it.
Upside: Less database trips. i.e two queries only.
3rd method
Looks like the second except that you can group messages by 'user_id' then you do no extra filter when transforming users result:
$user = DB::table('users')->get();
$messages = DB::table('messages')->whereIn('user_id', $user->pluck('id')->toArray())
->get()
->groupBy('user_id');
$result = $user->transform(function ($user) use ($messages){
$user->messages = $messages[$user->id];
return $user;
});
Downside: Same with two.
Upside: no extra filter when transforming users.
Other method
Join on both users and messages when querying then transform the response, or simply use it as it is.
PS: Eloquent uses query builder.
The answer is open for update.
I have a simple app, using Laravel 5.5.13.
public function index()
{
return Pet::all();
}
This lists all pets. I have many to many relation where many users can own a the same pet (the pet's human family).
I want to load those users.
Doing return Pet::with('users')->get(); does the trick, however it loads all kind of excessive infromation, like the users api_token etc, I just want to pick some fields, like id and name:
I was hoping to just get users: [1, 12] for the example in the screenshot above.
I tried pluck like this return Pet::with('users')->get()->pluck('id') but this gives me only the ids.
You can select specific fields like this:
Pet::with(['users' => function($query) { $query->select('id', 'name'); }])->get()
If you're only looking to get user IDs where all the matching users have at least one pet, you can try:
// Retrieve all users that have at least one pet
return User::has('pets')->get(['id']);
In case I'm misunderstanding you and you still want all of the Pet information, you can use a colon to fetch specific columns in a relation:
// Returns all Pets, along with their users' IDs
return Pet::with('users:id')->get();
Querying Relations, Querying Relationship Existence
Eager Loading, Eager Loading Specific Columns
I'm using laravel and eloquent.
Actually I have problems filtering results from a table based on conditions on another table's attributes.
I have 3 tables:
venue
city
here are the relationships:
a city has many locations and a location belongs to a city.
a location belongs to a venue and a venue has one location.
I have a city_id attribute on locations table, which you may figured out from relationships.
The question is simple:
how can I get those venues which belong to a specific city?
the eloquent query I expect looks like this:
$venues=Venue::with('location')->where('location.city_id',$city->getKey());
Of course that's not gonna work, but seems like this is common task and there would be an eloquent command for it.
Thanks!
A couple of options:
$venues = Venue::whereIn('location_id', Location::whereCityId($city->id)->get->lists('id'))
->get();
Or possibly using whereHas:
$venues = Venue::whereHas('location', function($query) use ($city) {
$query->whereCityId($city->id);
})->get();
It is important to remember that each eloquent query returns a collection, and hence you can use "collection methods" on the result. So as said in other answers, you need a Eager Loading which you ask for the attribute you want to sort on from another table based on your relationship and then on the result, which is a collection, you either use "sortBy" or "sortByDesc" methods.
You can look at an example below:
class Post extends Model {
// imagine timpestamp table: id, publish, delete,
// timestampable_id, timestampble_type
public function timestamp()
{
return $this->morphOne(Timestamp::class, 'timestampable');
}
}
and then in the view side of the stuff:
$posts = App\Post::with('timestamp')->get(); // we make Eager Loading
$posts = $posts->sortByDesc('timestamp.publish');
return view('blog.index', compact('posts'));