Eloquent-relationer

<?php
class User extends Model {
    public function profile(): \Illuminate\Database\Eloquent\Relations\HasOne {
        return $this->hasOne(Profile::class);
    }
}
// Access:
$profile = $user->profile;

<?php
class Profile extends Model {
    public function user(): \Illuminate\Database\Eloquent\Relations\BelongsTo {
        return $this->belongsTo(User::class);
    }
}
// Access:
$user = $profile->user;

<?php
class User extends Model {
    public function posts(): \Illuminate\Database\Eloquent\Relations\HasMany {
        return $this->hasMany(Post::class);
    }
}
// Access:
$posts = $user->posts; // Collection

<?php
class Post extends Model {
    public function author(): \Illuminate\Database\Eloquent\Relations\BelongsTo {
        return $this->belongsTo(User::class, "user_id");
    }
}

<?php
class Post extends Model {
    public function tags() {
        return $this->belongsToMany(Tag::class);
    }
}
// Pivot table: post_tag (post_id, tag_id)
$tags = $post->tags;
$post->tags()->attach($tagId);
$post->tags()->detach($tagId);
$post->tags()->sync([1, 2, 3]);

<?php
class Country extends Model {
    public function posts() {
        return $this->hasManyThrough(Post::class, User::class);
    }
}

<?php
class Comment extends Model {
    public function commentable() {
        return $this->morphTo();
    }
}
class Post extends Model {
    public function comments() {
        return $this->morphMany(Comment::class, "commentable");
    }
}

<?php
// Posts that have at least one comment:
$commented = Post::has("comments")->get();
// Posts with >= 3 comments:
$popular = Post::has("comments", ">=", 3)->get();

<?php
$phpPosts = Post::whereHas("tags", function ($q) {
    $q->where("name", "PHP");
})->get();