Fix https://github.com/firefly-iii/firefly-iii/issues/5852

app/Factory/TransactionCurrencyFactory.php

@@ -43,6 +43,15 @@ class TransactionCurrencyFactory
      */
     public function create(array $data): TransactionCurrency
     {
+        // if the code already exists (deleted)
+        // force delete it and then create the transaction:
+        $count = TransactionCurrency::withTrashed()->whereCode($data['code'])->count();
+        if(1 === $count) {
+            $old = TransactionCurrency::withTrashed()->whereCode($data['code'])->first();
+            $old->forceDelete();
+            Log::warning(sprintf('Force deleted old currency with ID #%d and code "%s".', $old->id, $data['code']));
+        }
+
         try {
             /** @var TransactionCurrency $result */
             $result = TransactionCurrency::create(

app/Http/Requests/CurrencyFormRequest.php

@@ -59,9 +59,9 @@ class CurrencyFormRequest extends FormRequest
     {
         // fixed
         $rules = [
-            'name'           => 'required|max:48|min:1|unique:transaction_currencies,name',
+            'name'           => 'required|max:48|min:1|uniqueCurrencyName',
-            'code'           => 'required|min:3|max:51|unique:transaction_currencies,code',
+            'code'           => 'required|min:3|max:51|uniqueCurrencyCode',
-            'symbol'         => 'required|min:1|max:51|unique:transaction_currencies,symbol',
+            'symbol'         => 'required|min:1|max:51|uniqueCurrencySymbol',
             'decimal_places' => 'required|min:0|max:12|numeric',
             'enabled'        => 'in:0,1',
         ];

app/Validation/FireflyValidator.php

@@ -53,6 +53,48 @@ use function is_string;
  */
 class FireflyValidator extends Validator
 {
+
+    /**
+     * @param $attribute
+     * @param $value
+     * @return bool
+     */
+    public function validateUniqueCurrencyName($attribute, $value): bool
+    {
+        return $this->validateUniqueCurrency('name', (string) $attribute, (string) $value);
+    }
+
+    /**
+     * @param $attribute
+     * @param $value
+     * @return bool
+     */
+    public function validateUniqueCurrencyCode($attribute, $value): bool
+    {
+        return $this->validateUniqueCurrency('code', (string) $attribute, (string) $value);
+    }
+
+    /**
+     * @param $attribute
+     * @param $value
+     * @return bool
+     */
+    public function validateUniqueCurrencySymbol($attribute, $value): bool
+    {
+        return $this->validateUniqueCurrency('symbol', (string) $attribute, (string) $value);
+    }
+
+    /**
+     * @param $attribute
+     * @param $value
+     * @return bool
+     */
+    public function validateUniqueCurrency(string $field, string $attribute, string $value): bool
+    {
+        return 0 === DB::table('transaction_currencies')->where($field, $value)->whereNull('deleted_at')->count();
+    }
+
+
     /**
      * @param mixed $attribute
      * @param mixed $value