How to use sequelize and promise correctly

Question

I'm learning how to write apps using expressJS and Sequelize. So please help me because I'm only used to use sequencial programming. I have 2 models Todo(id, title) and TodoItem(id, content, complete, todoId). I try to write function for changing TodoItem properties. If I'm changing content or complete value it's no problem to me. I know how to develope this. When on request there is todoId which is diffrent than actual value I want to check if todo with that Id exists. I wrote first method in todo controller which check it, but the problem is that it returns Promise, but I want to get Boolean. It looks like this:

exists(todoId) {
   Todo.findByPk(todoId)
      .then(todo => {
         if (!todo) {
            console.log(`[exists] Todo ${todoId} not exists`);
            return false;
         } else {
            console.log(`[exists] Todo ${todo.id} exists`);
            return true;
         }
      })
      .then(b => {
         console.log(`B = ${b}`)
      })
      .catch(error => { throw error });
}

It is possible to change from async to sync? I show you what I code in todoItem controller so you will imagine what I wanted to do.

update(req, res) {
        return TodoItem
            .findOne({
                where: {
                    todoId: req.params.todoId,
                    id: req.params.todoItemId
                }
            })
            .then(
                todoItem => {
                    if (!todoItem) {
                        return res.status(404).send({ message: 'TodoItem Not Found' });
                    }

                    if (req.body.todoId && todoItem.todoId != req.body.todoId) {
                        console.log(`Check if Todo ${req.body.todoId} exists`);
                        console.log(todosController.exists(req.body.todoId));
// Here I want to check if todo(req.body.todoId) not exists and if not, then 
//   res.status(404).send({ message: 'Todo Not Found' });

                    }

                    return todoItem
                        .update(req.body, { fields: Object.keys(req.body) })
                        .then(todoItem => res.status(200).send(todoItem))
                        .catch(error => res.status(400).send(error))
                }
            )
            .catch(error => {
                res.status(400).send(error);
            })
    }

Answer 1

You still can write an async code in a sequential -like way by using async and await keywords.

async exists(todoId) {
   const todo = await Todo.findByPk(todoId)
   if (!todo) {
     console.log(`[exists] Todo ${todoId} not exists`);
     return false;
   } else {
     console.log(`[exists] Todo ${todo.id} exists`);
     return true;
   }
}

and update looks like:

async update(req, res) {
     try {
        const todoItem = await TodoItem
            .findOne({
                where: {
                    todoId: req.params.todoId,
                    id: req.params.todoItemId
                }
            })
        if (!todoItem) {
          res.status(404).send({ message: 'TodoItem Not Found' });
          return
        }

        if (req.body.todoId && todoItem.todoId != req.body.todoId) {
          console.log(`Check if Todo ${req.body.todoId} exists`);
          const todoExists = await todosController.exists(req.body.todoId)
          console.log(todoExists);
          if (!todoExists) {
// Here I want to check if todo(req.body.todoId) not exists and if not, then 
            res.status(404).send({ message: 'Todo Not Found' });
            return 
          }
       }

       const updatedTodoItem = await todoItem
         .update(req.body, { fields: Object.keys(req.body) })
       res.status(200).send(updatedTodoItem)
     } catch(error) {
        res.status(400).send(error);
     }
}

Answer 2

OK, now my code is simple and works fine. If you have some valuable comments, eg best practise, please do so. In todo controller I have

exists(todoId) {
        return Todo.findByPk(todoId)
            .then(todo => {
                if (todo) {
                    return true;
                } else {
                    return false;
                }
            });
    }

and in todoItem controller:

update(req, res) {
        return TodoItem
            .findOne({
                where: {
                    todoId: req.params.todoId,
                    id: req.params.todoItemId
                }
            })
            .then(
                async (todoItem) => {
                    if (!todoItem) {
                        return res.status(404).send({ message: 'TodoItem Not Found' });
                    }

                    if (req.body.todoId && todoItem.todoId != req.body.todoId) {
                        if (!await todosController.exists(req.body.todoId))
                            return res.status(404).send({ message: 'Todo Not Found' });
                    }

                    return await todoItem
                        .update(req.body, { fields: Object.keys(req.body) })
                        .then(todoItem => res.status(200).send(todoItem))
                        .catch(error => res.status(400).send(error))
                }
            )
            .catch(error => res.status(400).send(error))
    }