使用 req,res 参数调用函数

Question

I'm making an API on NodeJS with Express. I have a function in the schema Products who return a product by id. The signature of this function is like this:

let getProductsById = (req, res) => {
    let id = req.params.id;
    Producto.findById(id)
        .populate('categoria')
        .populate('marca')
        .exec((err, producto) => {
            if (err) {
                return res.status(500).json({
                    ok: false,
                    error: err
                });
            }
            if (!producto) {
                return res.status(400).json({
                    ok: false,
                    error: {
                        message: 'Producto no encontrado'
                    }
                });
            }
            productoResponse = {
                _id: producto._id,
                codigo: producto.codigo,
                descripcion: producto.descripcion,
                nombre: producto.nombre,
                precioCosto: producto.precioCosto,
                precioVenta: producto.precioVenta,
                categoria: {
                    _id: producto.categoria._id,
                    nombre: producto.categoria.nombre
                },
                marca: {
                    _id: producto.marca._id,
                    nombre: producto.marca.nombre
                }
            }
            res.json({
                ok: true,
                producto: productoResponse
            });
        });
}

If you don't want to read the entire function, in resume this return a object with some info in it.

I call this function in the router like this:

app.get('/producto/:id', function(req, res) {
    getProductsById(req, res);
});

This works fine, but I want in another schema (Cart) to call this function to recive a product. In the service of Cart I have this function:

let addCart = (req, res) => {
    let body = req.body;
    let cart = new Cart({
        user: body.user,
        products: body.products,
        pay: body.pay,
        address: body.address,
        phone: body.phone,
        moreInfo: body.moreInfo,
        total: body.total
    });
    cart.products.forEach(product => {
        console.log(product._id);
        req.params.id = product._id;
        let productX = getProductsById(req,res);
    });
}

But this don't work, I have a error that says:

events.js:288
      throw er; // Unhandled 'error' event
      ^

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:526:11)
    at ServerResponse.header (C:\Users\Nacho\Desktop\node\07-restserver\node_modules\express\lib\response.js:771:10)
    at ServerResponse.send (C:\Users\Nacho\Desktop\node\07-restserver\node_modules\express\lib\response.js:170:12)
    at ServerResponse.json (C:\Users\Nacho\Desktop\node\07-restserver\node_modules\express\lib\response.js:267:15)
    at C:\Users\Nacho\Desktop\node\07-restserver\server\services\productService.js:57:40
    at C:\Users\Nacho\Desktop\node\07-restserver\node_modules\mongoose\lib\model.js:4832:16
    at C:\Users\Nacho\Desktop\node\07-restserver\node_modules\mongoose\lib\helpers\promiseOrCallback.js:24:16
    at C:\Users\Nacho\Desktop\node\07-restserver\node_modules\mongoose\lib\model.js:4855:21
    at C:\Users\Nacho\Desktop\node\07-restserver\node_modules\mongoose\lib\query.js:4407:11
    at C:\Users\Nacho\Desktop\node\07-restserver\node_modules\kareem\index.js:135:16
    at processTicksAndRejections (internal/process/task_queues.js:79:11)
Emitted 'error' event on Function instance at:
    at C:\Users\Nacho\Desktop\node\07-restserver\node_modules\mongoose\lib\model.js:4834:13
    at C:\Users\Nacho\Desktop\node\07-restserver\node_modules\mongoose\lib\helpers\promiseOrCallback.js:24:16
    [... lines matching original stack trace ...]
    at processTicksAndRejections (internal/process/task_queues.js:79:11) {
  code: 'ERR_HTTP_HEADERS_SENT'
}

How can I resolve this problem? Ty.

I resolve doing this way (don't follow my steps is bad and I need to restructure the code)

carrito.productos.forEach(producto => {
        console.log(producto._id);
        let id = producto._id;
        Producto.findById(id)
        .exec((err, productoObtenido) => {
            if (err) {
                return false;
            }
            if (!productoObtenido) {
                return false;
            }
            producto.precioVenta = productoObtenido.precioVenta;
        });
    });

Answer 1

Problem is here

cart.products.forEach(product => {
    console.log(product._id);
    req.params.id = product._id;
    let productX = getProductsById(req,res);
});

So you're calling res.send multiple time from getProductsById

They express refuse it.

Answer 2

I think you should restructure your app. Move your actual business logic on a layer behind the request and response handling. That way you can reuse services/functionality without passing the request and response objects around, which makes your code way harder to write and to understand.