Added the limitation so that the default currency and the currencies in use cannot be deleted.

src/accounting/currency/views.py

@@ -160,6 +160,9 @@ def delete_currency(currency: Currency) -> redirect:
     :return: The redirection to the currency list on success, or the currency
         detail on error.
     """
+    if not currency.can_delete:
+        flash(s(lazy_gettext("The currency cannot be deleted.")), "error")
+        return redirect(inherit_next(__get_detail_uri(currency)))
     currency.delete()
     db.session.commit()
     flash(s(lazy_gettext("The currency is deleted successfully.")), "success")

src/accounting/models.py

@@ -432,6 +432,17 @@ class Currency(db.Model):
                 return True
         return False
 
+    @property
+    def can_delete(self) -> bool:
+        """Returns whether the currency can be deleted.
+
+        :return: True if the currency can be deleted, or False otherwise.
+        """
+        from accounting.template_globals import default_currency_code
+        if self.code == default_currency_code():
+            return False
+        return len(self.line_items) == 0
+
     def delete(self) -> None:
         """Deletes the currency.
 

src/accounting/templates/accounting/currency/detail.html

@@ -37,10 +37,17 @@ First written: 2023/2/6
     </a>
   {% endif %}
   {% if accounting_can_edit() %}
-    <button class="btn btn-danger" type="button" data-bs-toggle="modal" data-bs-target="#accounting-delete-modal">
-      <i class="fa-solid fa-trash"></i>
-      <span class="d-none d-md-inline">{{ A_("Delete") }}</span>
-    </button>
+    {% if obj.can_delete %}
+      <button class="btn btn-danger" type="button" data-bs-toggle="modal" data-bs-target="#accounting-delete-modal">
+        <i class="fa-solid fa-trash"></i>
+        <span class="d-none d-md-inline">{{ A_("Delete") }}</span>
+      </button>
+    {% else %}
+      <button class="btn btn-secondary" type="button" disabled="disabled">
+        <i class="fa-solid fa-trash"></i>
+        <span class="d-none d-md-inline">{{ A_("Delete") }}</span>
+      </button>
+    {% endif %}
   {% endif %}
 </div>
 
@@ -52,7 +59,7 @@ First written: 2023/2/6
   </div>
 {% endif %}
 
-{% if accounting_can_edit() %}
+{% if accounting_can_edit() and obj.can_delete %}
   <form action="{{ url_for("accounting.currency.delete", currency=obj) }}" method="post">
     <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
     {% if request.args.next %}