Laravel HasMany relationship not giving expected result - php

Question

I have three table with following columns:
posts table
id
author
title
content
seen
post_img
post_category table
id
category_id
post_id
categories table
id
category
I created post_category table to store post catergories. I wanted to get posts that have specific category. And i created my PostModel associated with posts table like this:
use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use App\Models\AuthorModel;
use App\Models\PostCategoryModel;
use App\Models\CategoryModel;
class PostModel extends Model
{
use HasFactory;
protected $table = 'posts';
public function getAuthor(){
return $this->hasOne(AuthorModel::class, 'id', 'author');
}
public function getCategories(){
return $this->hasMany(PostCategoryModel::class, 'post_id', 'id');
}
}
After i got the PostCategoryModel from calling getCategories method, i created PostCategoryModel associated with post_category table like this:
use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use App\Models\CategoryModel;
use App\Models\PostModel;
class PostCategoryModel extends Model
{
use HasFactory;
protected $table = 'post_category';
public function getCategory(){
return $this->hasMany(CategoryModel::class, 'id', 'category_id');
}
public function getPosts(){
return $this->belongsToMany(PostModel::class, 'id', 'post_id');
}
}
But here is the problem, when i call PostModel::getCategories in my Controller method it gives me this error: Undefined constant App\Models\PostModel::getCategories. How can i get categories of a post in my case?
Laravel version: Laravel Framework 8.22.1
PHP version: PHP 8.0.1 (cli) (built: Jan 5 2021 23:43:33) ( NTS Visual C++ 2019 x64 )

Answer 1

As I know you can't call relation methods like static method cause it needs an instance to check its id and match with other table. You can use something like this:
$cats = PostModel::find(1)->getCategories();
But it's just an example and in real application you probably use route model binding or anything else.

Answer 2

I believe you have a many to many relation between post and category, If so then you don't need intermediate model for junction table post_category unless you have another specific reason to introduce model for this table.
For many to many relationship you need to adjust your post and category models as
class Post extends Model
{
//.. Other methods
public function categories(){
return $this->belongsToMany(Category::class, 'post_category', 'post_id', 'category_id');
}
}
class Category extends Model
{
//.. Other methods
public function posts(){
return $this->belongsToMany(Post::class, 'post_category', 'category_id','post_id');
}
}
I wanted to get posts that have specific category
Once you have proper relations in place you can get posts for specific category using whereHas()
$posts = Post::whereHas('categories', function (Builder $query) use($category_id) {
$query->where('id', $category_id);
})->get();
How can i get categories of a post in my case?
To get categories associated with posts you can eager load them as
$posts = Post::with('categories')
->whereHas('categories', function (Builder $query) use($category_id) {
$query->where('id', $category_id);
})->get();