JsonMapper

The @tsed/json-mapper package is responsible to map a plain object to a model and a model to a plain object.

It provides two functions serialize and deserialize to transform object depending on which operation you want to perform. It uses all decorators from @tsed/schema package and TypeScript metadata to work.

Ts.ED use this package to transform any input parameters sent by your consumer to a class and transform returned value by your endpoint to a plain javascript object to your consumer.

Configuration

@Configuration({
  jsonMapper: {
    additionalProperties: false,
    disableUnsecureConstructor: false,
  }
})

jsonMapper.additionalProperties

Enable additional properties on model. By default, false. Enable this option is dangerous and may be a potential security issue.

jsonMapper.disableUnsecureConstructor

Pass the plain object to the model constructor. By default, true.

It may be a potential security issue if you have as constructor with this followings code:

class MyModel {
  constructor(obj: any = {}) {
    Object.assign(this, obj); // potential prototype pollution
  }
}

Usage

JsonMapper works with a class and decorators. Use decorators on properties to describe a model and use this model as an input parameter or return value by your endpoint. Here is a model example:

Note

Take a look on Jest/Mocha tabs to see serialize and deserialize functions usage.

Now we can use the Person model on a controller:

import {BodyParams} from "@tsed/platform-params";
import {Get, Post, Returns} from "@tsed/schema";
import {Controller} from "@tsed/di";
import {Person} from "../models/Person";

@Controller("/")
export class PersonsCtrl {
  @Post("/")
  @Returns(200, Person)
  async save1(@BodyParams() person: Person): Promise<Person> {
    console.log(person instanceof Person); // true

    return person; // will be serialized according to your annotation on Person class.
  }

  // OR
  @Post("/")
  @Returns(200, Person)
  async save2(@BodyParams("person") person: Person): Promise<Person> {
    console.log(person instanceof Person); // true

    return person; // will be serialized according to your annotation on Person class.
  }

  @Get("/")
  @Returns(200, Array).Of(Person) // Add the correct json schema for swagger essentially.
  async getPersons(): Promise<Person[]> {
    return [new Person()];
  }
}

Note

In the previous example, we can see Returns decorator usage. In all case, Ts.ED infer the returned value and apply the correct transformation on your response.

Returns decorator is used to generate the correct swagger documentation only.

WARNING

When a model is provided, JsonMapper will follow exactly the JsonSchema generated by @tsed/schema package.

It means, if you missed decorating one or more properties on your model, these properties won't be appear after the transformation.

Note: Result is displayed in Jest/Mocha tabs.

Ignore properties

Usage

Ignore decorator can be used to ignore explicitly a property when a transformation have been performed.

For example, you have a base model to create a User named UserCreation where the password is required, but you don't want to expose this field in other cases. One of the solution is to use class inheritance to solve this problem.

With a callback

Ignore decorator since v6.13.0 accept a callback which will be called when a property have been serialized or deserialized. The callback will give you more control over the way to ignore a property.

class User {
  @Name("id")
  _id: string;

  @Property()
  firstName: string;

  @Property()
  lastName: string;

  @Ignore((value, ctx) => ctx.endpoint) // should not serialized when the object is returned by an endpoint.
  password: string;

  @Ignore((value, ctx) => ctx.mongoose) // should be serialized when the object is returned by an endpoint.
  scopes: string[];

  @Ignore()
  alwaysIgnored: string;
}

Here is the available options on ctx:

Prop	Type	Description
endpoint	boolean	It's an endpoint context
mongoose	boolean	It's a mongoose context

Additional properties

AdditionalProperties decorator can be used to accept any additional properties on a specific model.

Alias

Name decorator lets you to rename the exposed property in your json schema.

For example mongo db uses the _id property. In order not to give any indication to our consumer about the nature of the database, it's better to rename the property to id.

import {Description, Example, Name} from "@tsed/schema";
import {ObjectID} from "@tsed/mongoose";

export class Model {
  @Name("id")
  @Description("Object ID")
  @Example("5ce7ad3028890bd71749d477")
  _id: string;
}

// same example with mongoose
export class Model2 {
  @ObjectID("id")
  _id: string;
}

OnSerialize

OnSerialize decorator can be used to intercept and change the property value when a serialization is performed on class.

import {OnSerialize} from "@tsed/schema";

export class Person {
  @OnSerialize((v) => v + "Test")
  property: string;
}

OnDeserialize

OnDeserialize decorator can be used to intercept and change the property value when a deserialization is performed on class.

import {OnDeserialize} from "@tsed/schema";

export class Person {
  @OnDeserialize((v) => v + "Test")
  property: string;
}

Type mapper

@tsed/json-mapper use classes to transform an input value to the expected value:

Type	Mapper
Primitives	PrimitiveMapper ,
Symbol	SymbolMapper ,
Objects	DateMapper ,
Collections	ArrayMapper , MapMapper and SetMapper .

It's possible to add your own type mapper by using the JsonMapper decorator on a class. Just copy a mapper implementation and import the mapper in your application.

Primitives

PrimitiveMapper is responsible to map the primitive value like Boolean, Number or String.

Cheat sheet

Input	Type	Output
1	String	"1"
"1"	String	"1"
null	Number	null
"null"	Number	null
"1"	Number	1
1	Number	1
"to1"	Number	Throw Bad Request. This is the only case where JsonMapper throw a cast type error.
true	Boolean	true
"true"	Boolean	true
"1"	Boolean	true
1	Boolean	true
false	Boolean	false
"false"	Boolean	false
"0"	Boolean	false
0	Boolean	false
""	Boolean	false
"null"	Boolean	null
undefined	Boolean	undefined

Symbol

SymbolMapper is responsible to map a String to Symbol or a Symbol to a String.

Date

DateMapper is responsible to map a Number, String to a Date or a Date to a String.

Array

ArrayMapper is responsible to map any data to an Array.

Map

MapMapper is responsible to map an Object to a Map.

Set

SetMapper is responsible to map an Array to a Set.

Create your own type mapper

It's possible de to change add your own type mapper by using the JsonMapper decorator on a class. Just copy a mapper implementation and import the mapper in your application.

A mapper must declare the type it must work on and implement two methods: serialize and deserialize.

import {JsonMapper, JsonMapperMethods, JsonMapperCtx} from "@tsed/json-mapper";

@JsonMapper(String)
export class TheTypeMapper implements JsonMapperMethods {
  deserialize(data: any, ctx: JsonMapperCtx): String {
    return JSON.stringify(data) + ":deserialize";
  }

  serialize(data: any, ctx: JsonMapperCtx): String {
    return JSON.stringify(data) + ":serialize";
  }
}

Then import your new mapper in your Server.ts as following:

import {Configuration} from "@tsed/di";

import "./mappers/TheTypeMapper";

@Configuration({
  mount: {
    "/rest": []
  }
})
export class Server {}

Moment

Moment.js (opens new window) is a powerful library to transform any formatted date string to a Moment instance.

You can change the Date mapper behavior to transform string to a Moment instance.