DTO-Maker

The DTO Maker servers two purposes:

• Generate schema from DTO interface
• parse (and validate) object as DTO interface according to provided schema

Requirements:

• Typescript

Generate schema

Use the createSchemaFromInterface method to return a json object of an interface. Path to interface file and its name is required.

Given: ./dto/hello-world.dto.ts:

/* Description of interface */
export interface IHelloWorldDTO {
  /* Object ID */
  id: number;
  name: string;
  // Description is optional
  description?: string;
}

...using...

import ts from "ts";

const schema = createSchemaFromInterface(
  "./dto/hello-world.dto.ts",
  "IHelloWorldDTO",
  ts,
);

console.log(schema);

Will output:

{
  "name": "IHelloWorldDTO",
  "description": "Description of interface",
  "properties": [
    {
      "name": "id",
      "description": "Object ID",
      "type": "number"
    },
    {
      "name": "name",
      "type": "string"
    },
    {
      "name": "description",
      "description": "Description is optional",
      "type": "string",
      "optional": true
    }
  ]
}

Method supports array types and complex types (like reference to other interfaces).

Parse DTO object using schema

Using the above schema an object can be parsed as interface using the parseDTOFromJson method.

parseDTOFromJson([schema], {
  id: 1,
  name: "MyName",
  description: "",
}, "IHelloWorldDTO");

The method will throw an error if object does not fit schema. Error message tries to be as descriptive as possible

Working with multiple interfaces

If an interface reference another interface, schema for that interface must be provided as well when trying to parse.

Example:

Given: another.dto.ts:

export interface IAnotherDTO {
  id: number;
  tags: string[];
}

...and hello-world.dto.ts:

export interface IHelloWorldDTO {
  id: number;
  name: string;
  description?: string;
  another: IAnotherDTO;
}

...using...

import ts from "ts";

// Generate schemas for interfaces
const schemas = [
  createSchemaFromInterface(
    "./dto/hello-world.dto.ts",
    "IHelloWorldDTO",
    ts,
  ),
  createSchemaFromInterface(
    "./dto/another.dto.ts",
    "IAnotherDTO",
    ts,
  ),
];

// Parse object using schemas
parseDTOFromJson(schemas, {
  id: 1,
  name: "MyName",
  description: "",
  another: {
    id: 1,
    tags: ["a", "b", "c"]
  }
}, "IHelloWorldDTO");

Anecdote

The lib was written to easier parse JSON-objects coming from HTTP requests without needing to write individual parser for each DTO interface.

A great way of using this lib is to create a npm/yarn command for generating schemas for all your DTO interfaces into a big json schema file. Later this file can be referenced any time you wanna parse a json object coming from a HTTP response.

Remember that this only helps casting the object and has no way of validating data. It only checks data type.