I'm studying where queries.
I would like to use two where query. I wrote the below code but I couldn't get any records.
Could you teach me the right code, please?
public function band()
{
$images = ImageGallery::where(DB::raw('LEFT(image, 2)'), '02')->
where(DB::raw('LEFT(image, 2)'), '03')->get();
return view('band',compact('images'));
}
Related
I'm currently working on a simple Laravel project where I need to get the posts of the users I'm following. With the code below, I can get the posts but I also add a lot of duplicate queries and an N+1 issue on the Authenticated user. So it's becoming sort of a head scratcher. I've looked though other similar scenarios online but I haven't been able to pinpoint what I'm doing wrong. Perhaps there is a better way. Currently, I have on the User model:
public function usersImFollowing()
{
return $this->belongsToMany(User::class, 'follow_user', 'user_id', 'following_id')
->withPivot('is_following', 'is_blocked')
->wherePivot('is_following', true)
->wherePivot('is_blocked', false)
->paginate(3);
}
public function userPosts()
{
return $this->hasMany(Post::class, 'postable_id', 'id')
->where('postable_type', User::class);
}
As you can see, I am using two booleans to determine if a user is following or is blocked. Also, the Post model is a polymorphic model. There are several things I've tried, among them, I tried a hasManyThrough, without using the hasMany Posts relationship above. It got the posts for each user but since I'm using the booleans above, I couldn't use them in the hasManyThrough, it simply got the posts based on the following_id, whether or not the user was following or was blocked became irrelevant.
Then in a separate service class, I tried the methods below (I'm using a separate class to maintain the code easier). They both get the posts for each user but add an N+1 problem and 12 duplicate queries based on 5 posts from 2 users. I will also need to filter the results based on some conditions, so it will probably add more queries. Additionally, I'm using a Laravel resource collection that would pull other items for each post, such as images, comments, etc., so the amount of queries would increase even more. Not sure, perhaps I'm doing too much and there is an easier way:
Either:
$following = $request->user()->usersImFollowing();
$posts = $following->map(function($user){
return $user->userPosts()->get();
})->flatten(1);
return $posts;
Or
$postsfromfollowing = [];
$following = $request->user()->usersImFollowing()->each(function($user) use (&$postsfromfollowing){
array_push($postsfromfollowing,$user->userPosts);
});
$posts = Arr::flatten($postsfromfollowing);
return $posts;
Maybe you could use scopes to do little celanup of code and generated sql.
In User model something like
public function scopeIsFollowedBy(Builder $query, int $followerId) {
return $query->where('following_id', '=', $followerId);
}
And in Post model
public function scopeIsFollowedBy(Builder $query, int $followerId) {
return $query->whereHas('user', function($q) use ($followerId) {
$q->isFollowedBy($followerId);
});
}
You can use it then in coltroller like any other condition like this:
Post::isFollowedBy($followerId)->...otherConditions...->get();
The SQL generated won't go through foreach but only add one IF EXISTS select (generated by whereHas part of the code)
More on local scopes in Laravel is here https://laravel.com/docs/8.x/eloquent#local-scopes
I'm studying laravel query builder's "count"
I would like to count column name 'q12a' and 'q18a'
I can count total records useing below code.
public function count()
{
$total_projects = Book::count();
return view('count')->with(['total'=>$total_projects]);
}
However I'm having problem multiple columns
I had been searching count multiple columns and trying below code and I got
Error Call to a member function count() on int
Dear matiaslauriti helping me and I change code as below.
UPDATED
public function sum_ttl()
{
$q18a_count = DB::table('books')->count('q12a')->count('q18a');
return view('sum_ttl', compact('q12a','q18a'));
}
Could you teach me how to write correct code at controller and blade file please?
You are nearly there. count will return the count of your desired columns (* by default). So you want to do something like:
public function sum_ttl()
{
$q12aCount = Books::count('q12a');
$q18aCount = Books::count('q18a');
return view('sum_ttl', compact('q12aCount', 'q18aCount'));
}
If you want to share the exact SQL query you want to execute, I could try to "translate" it to Eloquent.
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.
after some digging I still could not find any solid way to retrieve the inverse of a many-to-many polymorphic relation that allows mixed models results.
Please consider the following:
I have several models that can be "tagged". While it is trivial to retrieve for example $item->tags, $article->tags and the inverse with $tag->articles and $tag->items I have no easy way to do something like $tag->taggables to return both articles and items in the same collection. Things get even bumpier as I need to use pagination/simple pagination to the query.
I have tried a few workarounds but the best I could put together still looks crappy and limited. Basically:
I queried the DB once per "taggable";
put all in a single big collection;
passed the collection to a phpleague/fractal transformer (my API uses it) that returns different json values depending on the parsed models.
The limits of this approach is that building a pagination is a nightmare and fractal "include" options can't be used out of the box.
Can anyone help me? I'm currently using Laravel 5.1.
There is not much magic in my current code. Faking and simplifying it to make it short:
From the api controller:
$tag = Tag::findOrDie($tid);
$articles = $tag->cms_articles()->get();
$categories = $tag->cms_categories()->get();
$items = $tag->items()->simplePaginate($itemsperpage);
$taggables = Collection::make($articles)->merge($categories);
// Push items one by one as pagination would dirt the collection struct.
foreach ($items as $item) {
$taggables->push($item);
}
return $this->respondWithCollection($taggables, new TaggableTransformer);
Note: using simplePaginate() is there only because I would like all articles and categories to be shown on first page load while the number of items are so many that need pagination.
From the Transformer class:
public function transform($taggable)
{
switch (get_class($taggable)) {
case 'App\Item':
$transformer = new ItemTransformer;
break;
case 'App\CmsArticle':
$transformer = new CmsArticleTransformer;
break;
case 'App\CmsCategory':
$transformer = new CmsCategoryTransformer;
break;
}
return $transformer->transform($taggable);
}
Please consider that the other transformers are simply returning arrays of data about the models they correlate with. If you use Fractal you would easily spot that nested "included" models would not be applied.
Nothing fancy for the Tag model:
class Tag extends Model
{
protected $morphClass = 'Tag';
protected $fillable = array('name', 'language_id');
public function cms_articles() {
return $this->morphedByMany('App\CmsArticle', 'taggable');
}
public function cms_categories() {
return $this->morphedByMany('App\CmsCategory', 'taggable');
}
public function items() {
return $this->morphedByMany('App\Item', 'taggable');
}
// Would love something like this to return inverse relation!! :'(
public function taggables() {
return $this->morphTo();
}
}
I am also considering the option to do 3 separate calls to the API to retrieve articles, categories and items in three steps. While in this particular scenario this might make sense after all, I would still need to deal with this particular inverse relation headache with another part of my project: notifications. In this particular case, notifications would have to relate to many different actions/models and I would have to retrieve them all in batches (paginated) and sorted by model creation date...
Hope this all makes sense. I wonder if a completely different approach to the whole inverse "polymorphic" matter would help.
Kind regards,
Federico
Ah yes. I was down your path not all that long ago. I had the same nightmare of dealing with resolving the inverse of the relationship of polymorphic relationships.
Unfortunately polymorphic relationships haven't been given much attention in the Laravel ecosystem. From afar they look like unicorns and rainbows but soon you're fighting things like this.
Can you post an example of a $thing->taggable for a better picture? Think it may be solvable with a dynamic trait + accessor magic.
I'm trying to create a tag cloud in Laravel 4.1, tags can belong to many posts, and posts can have many tags. I'm using a pivot table to achieve this (post_tag).
So far I've come up with this to fetch the tags and check how many times it's used:
public static function tagCloud($tags, $max = 10) {
foreach($tags->toArray() as $tag) {
$count = DB::table('post_tag')
->where('tag_id', $tag['id'])
->count();
$cloud[$tag['slug']] = $count;
}
sd($cloud);
}
I pass Tag::all() to the above function. Obviously that's going to fire a crazy amount of queries on the database, which is what I'm trying to avoid. Normally you'd use eager loading to fix this problem, but it seems the documentation does not mention anything about eager loading pivot tables in combination with aggregates.
I hope someone can shine a light on how to optimize this current function or can point me in the right direction of a better alternative.
Sometimes it's just hard reduce them, but Laravel Cache is your friend:
$users = DB::table('users')->remember(10)->get();
It will remember your query for 10 minutes.
I believe you have a many-to-many relationship with posts in your tags table like this:
public function posts()
{
return $this->belongsToMany('Post');
}
So, you are able to do something like this:
$tags = Tag::with('posts')->get();
Then you may loop though the tags to find out how many posts each tag contains, like this:
foreach($tags as $tag) {
$tag->posts->count();
};
So, you may write your function like this:
public function scopeTagCloude($query) {
$cloud = [];
$query->with('posts')->get()->each(function($tag) use (&$cloud) {
$cloud[$tag['slug']] = $tag->posts->count();
});
return $cloud;
}
You may call this function like this:
$tagCloude = Tag::tagCloude();
If you dd($tagCloude) then you'll get something like this (example is taken from my blog app):
array (size=4)
'general' => int 4
'special' => int 5
'ordinary' => int 5
'extra_ordinary' => int 2