Extend invoices and invoice items to keep more information.

app/Models/Invoice.php

@@ -23,6 +23,13 @@ class Invoice extends Model
         'status',
         'sum',
         'tax',
+        'project_id',
+        'project_count',
+        'is_template',
+        'currency_code',
+        'due_date',
+        'cash_discount',
+        'cash_discount_date',
     ];
 
     /**
@@ -36,6 +43,25 @@ class Invoice extends Model
         'localized_state'
     ];
 
+    /**
+     * Set the project_count variable automatically, if a project is related to this invoice.
+     */
+    public static function boot(): void
+    {
+        parent::boot();
+        self::creating(function (Invoice $invoice) {
+            if (is_null($invoice->project_id)) {
+                return true;
+            }
+            if ($invoice->type != '326') {
+                return true;
+            }
+            $projectMax = Invoice::where('project_id', '=', $invoice->project_id)->max('project_count') + 1;
+            $invoice->project_count = $projectMax;
+            return true;
+        });
+    }
+
     /**
      * Get the invoice state as translated string.
      */
@@ -107,4 +133,9 @@ class Invoice extends Model
     {
         return $this->hasMany(Payment::class);
     }
+
+    public function project(): BelongsTo
+    {
+        return $this->belongsTo(Project::class);
+    }
 }