feat: error when starting BAL if user already has an ongoing one

src/entities/bal.rs

@@ -25,6 +25,11 @@ pub enum BalState {
     Ended
 }
 
+pub async fn get_user_ongoing_bal<C>(db_conn: &C, user_id: u32) -> Option<Model>
+where C: ConnectionTrait {
+    Entity::find().filter(Column::UserId.eq(user_id)).filter(Column::State.eq(BalState::Ongoing)).one(db_conn).await.unwrap_or(None)
+}
+
 #[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
 pub enum Relation {
     #[sea_orm(has_many = "super::book_instance::Entity")]