project/app/Models/Invoice.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsTo;
use Illuminate\Database\Eloquent\Relations\HasMany;

class Invoice extends Model
{
    /**
     * The attributes that are mass assignable.
     *
     * @var array<int, string>
     */
    protected $fillable = [
        'user_id',
        'customer_id',
        'address_id',
        'delivery_id',
        'invoice_number',
        'type',
        'status',
        'sum',
        'tax',
        'project_id',
        'project_count',
        'is_template',
        'currency_code',
        'due_date',
        'cash_discount',
        'cash_discount_date',
    ];

    /**
     * The attributes that are appended with attribute getters.
     *
     * @var string[]
     */
    protected $appends = [
        'created',
        'number',
        'localized_state'
    ];

    /**
     * Get the invoice state as translated string.
     */
    public function getLocalizedStateAttribute(): string
    {
        return __('invoice.state_' . $this->status);
    }

    /**
     * Get the invoice number formatted
     */
    public function getNumberAttribute(): string
    {
        return $this->created_at->format('Y') . '-' . str_pad($this->invoice_number, 5, '0', STR_PAD_LEFT);
    }

    /**
     * Get the created_at attribute in local time format.
     */
    public function getCreatedAttribute(): string
    {
        return $this->created_at->format('d.m.Y');
    }

    /**
     * Get the user, that has created the invoice.
     */
    public function user(): BelongsTo
    {
        return $this->belongsTo(User::class);
    }

    /**
     * Get the invoice's customer.
     */
    public function customer(): BelongsTo
    {
        return $this->belongsTo(Customer::class)->withTrashed();
    }

    /**
     * Get the invoice's address.
     */
    public function address(): BelongsTo
    {
        return $this->belongsTo(Address::class)->withTrashed();
    }

    /**
     * Get the invoice's delivery address.
     */
    public function delivery(): BelongsTo
    {
        return $this->belongsTo(Address::class)->withTrashed();
    }

    /**
     * Get the items (invoice positions) of this invoice.
     */
    public function items(): HasMany
    {
        return $this->hasMany(Invoiceitem::class);
    }

    /**
     * Get the payments for the invoice
     */
    public function payments(): HasMany
    {
        return $this->hasMany(Payment::class);
    }

    public function project(): BelongsTo
    {
        return $this->belongsTo(Project::class);
    }
}