Virtual Field Decorators

Express-Cargo provides decorators to define virtual fields and request-derived fields. These decorators allow you to compute values dynamically or map data from the Request directly into the Object property.

Built-in Virtual Decorators

@Virtual<T>(transformer: (obj: object) => T)

The @Virtual decorator defines a computed property that is not directly sourced from the request. Instead, its value is derived from other properties of the object.

• transformer: A function that receives the object instance and returns the computed value

@Request<T>(transformer: (req: Request) => T)

The @Request decorator maps a value from the Express Request object into a class property.

• transformer: A function that receives the Request object and returns the value to bind.

Usage Example

import express from 'express'
import { Body, Virtual, Request, bindingCargo, getCargo } from 'express-cargo'

// 1. Define Object with virtual and request-derived fields
class OrderExample {
    @Body('price')
    price!: number

    @Body('quantity')
    quantity!: number

    // Computed field not present in the request
    @Virtual((obj: OrderExample) => obj.price * obj.quantity)
    total!: number
}

class HeaderExample {
    // Field derived directly from the request object
    @Request(req => req.headers['x-custom-header'] as string)
    customHeader!: string
}

// 2. Setup Express app and route
const app = express()
app.use(express.json())

app.post('/orders', bindingCargo(OrderExample), (req, res) => {
    const orderData = getCargo<OrderExample>(req)
    res.json({
        message: 'Order data processed with virtual fields!',
        data: orderData
    })
})

app.post('/headers', bindingCargo(HeaderExample), (req, res) => {
    const headerData = getCargo<HeaderExample>(req)
    res.json({
        message: 'Header data mapped using @request!',
        data: headerData
    })
})

/*
To test these endpoints, send POST requests with the relevant body or headers:

Example /orders body:
{
    "price": 50,
    "quantity": 2
}

Example /headers headers:
x-custom-header: my-header-value
*/