ExpectBody is a decorator which helps you to validate body data. It provides following features -

• Check data type of incoming body data against expected body.
• Removes unnecessary data from incoming body. This helps you to store data in nosql database without retrieving particular property and thus saving lots of code.

Check data type

Consider a post request which sends following data in request

{
    price:"1200",
    name:"black jeans nike"
}

Here price being sent is 1200 which is string but server expects it to be number. In this case you will write codes to check for data type of price property.

But when using ExpectBody it will automatically check the datatype & if not matches then returns a 400 request. This saves you writing code for validation of property type.

Let's see how to configure this using ExpectBody

export class ProductController{

    @Route("/")
    @Worker("post")
    @ExpectBody({ price:0, name:""})
    saveProduct(){
       const product =  this.body;
    }
}

You can also provide a class as parameter. Make sure that class properties are initialized.

e.g -

export class Product {
  price = 0;
  name = ""
}

export class ProductController{

    @Route("/")
    @Worker("post")
    @ExpectBody(Product)
    saveProduct(){
       const product =  this.body;
    }
}

Removes unnecessary data from incoming body

Consider a post request which sends following data in request

{
    name:"ujjwal gupta",
    gender:"male",
    extra:"some extra value" // some extra value which is not required
}

now for such requests -

1. We either save the whole data

export class UserController{

    @Route("/")
    @Worker("post")
    saveUser(){
       const user = this.body;
       // save user into mongodb
       const service = new UserService();
       service.saveUser(user);
    }
}

In this case - property extra will be saved too & thus your database has now garbage value. This is a very big risk & you shouldn't save data this way when using nosql database.

2. Extract particular value from body

export class UserController{

    @Route("/")
    @Worker("post")
    saveUser(){
       const user = {
           name:this.body.name,
           gender: this.body.gender
       } ;
       // save user into mongodb
       const service = new UserService();
       service.saveUser(user);
    }
}

this is a good way but consider user value with 10 properties which means you need to write 10 lines of code.

Let's write the above code using ExpectBody

export class UserController{

    @Route("/")
    @Worker("post")
    @ExpectBody({name:"", gender: ""})
    saveUser(){
       const user =  this.body;
       // save user into mongodb
       const service = new UserService();
       service.saveUser(user);
    }
}