Ways to dynamically link a JSON response object to an entity?

Question

Ways to dynamically link a JSON response object to an entity?

In my ng2 implementation, I have a user.service.ts file that calls a REST service and returns JSON data. The code snippet below shows how the getUser function retrieves the user information:

getUser(id: number): Promise<User> {
    return this.http.get('http://localhost:4000/users/1')
        .toPromise()
        .then(response => response.json())
}

The JSON object returned from the service has the following structure:

{
   "Id":"1"
   "FirstName":"John"
   "LastName":"Smith"
}

I want to convert this JSON object into an instance of my ng2 User entity, which is defined as follows:

export class User 
{
    Id: number;
    FirstName: string;
    LastName: string;
}

I am looking for a generic way to map the userResponse to the User entity without writing explicit mapping code each time. Ideally, I would like to automate this process using reflection or similar dynamic techniques. Is there a recommended approach to achieve this in ng2?

javascript angular typescript

Answer 1

Answer №1

It appears from the feedback that you aim to avoid implementing a constructor in your class. A straightforward approach to achieve this is by utilizing Object.assign():

fetchUser(id: number): Promise<User> {
  return this.http.get('http://api.example.com/users/1')
    .map(response => Object.assign(new User(), response.json()))
    .toPromise()
}

Your retrieved data will now be an instance of User.

Try it out here: (monitor the console for output)

Answer 2

It appears from the feedback that you aim to avoid implementing a constructor in your class. A straightforward approach to achieve this is by utilizing Object.assign():

fetchUser(id: number): Promise<User> {
  return this.http.get('http://api.example.com/users/1')
    .map(response => Object.assign(new User(), response.json()))
    .toPromise()
}

Your retrieved data will now be an instance of User.

Try it out here: (monitor the console for output)

Answer 3

Answer №2

To extract the keys of your json object's properties, iterate through them and assign each one to your object's properties using their respective names.

.then(json => {
    Object.keys(json).forEach(key => user[key] = json[key]);
});

If you prefer a reusable function, you can create one like this:

export class User {
    // declare properties here
    mapResponse(response) {
        Object.keys(response).forEach(key => this[key] = response[key]);
    }
}

getUser(id: number): Promise<User> {
    var user = new User();

    this.http.get('http://localhost:4000/users/1')
        .toPromise()
        .then(response => response.json())
        .then(newUser.mapResponse);

    return user;
}

This is my first attempt at writing TypeScript, so I hope this helps you get started in the right direction.

Answer 4

To extract the keys of your json object's properties, iterate through them and assign each one to your object's properties using their respective names.

.then(json => {
    Object.keys(json).forEach(key => user[key] = json[key]);
});

If you prefer a reusable function, you can create one like this:

export class User {
    // declare properties here
    mapResponse(response) {
        Object.keys(response).forEach(key => this[key] = response[key]);
    }
}

getUser(id: number): Promise<User> {
    var user = new User();

    this.http.get('http://localhost:4000/users/1')
        .toPromise()
        .then(response => response.json())
        .then(newUser.mapResponse);

    return user;
}

This is my first attempt at writing TypeScript, so I hope this helps you get started in the right direction.

Answer 5

Answer №3

Creating a constructor within your class declaration allows you to properly initialize the class:

export class User 
{
    Id: number;
    FirstName: string;
    LastName: string;
    constructor(obj: any) {
      this.Id = +obj['Id'];
      this.FirstName = obj['FirstName'];
      this.LastName = obj['LastName'];      
    }
}

To see it in action, check out this plunker.

If you need to dynamically set and reset values, you can create a method like this:

let user = setUser(this.userResponse); // <-- Assuming this.userResponse is the returned object

setUser(res) {
  return {
    Id: +res['Id'],
    FirstName: res['FirstName'],
    LastName: res['LastName']
  };
}

Answer 6

Creating a constructor within your class declaration allows you to properly initialize the class:

export class User 
{
    Id: number;
    FirstName: string;
    LastName: string;
    constructor(obj: any) {
      this.Id = +obj['Id'];
      this.FirstName = obj['FirstName'];
      this.LastName = obj['LastName'];      
    }
}

To see it in action, check out this plunker.

If you need to dynamically set and reset values, you can create a method like this:

let user = setUser(this.userResponse); // <-- Assuming this.userResponse is the returned object

setUser(res) {
  return {
    Id: +res['Id'],
    FirstName: res['FirstName'],
    LastName: res['LastName']
  };
}

Answer 7

Answer №4

For my project, I've opted to utilize Observables instead of Promises in my code. Here is an example:

getUserDetails(id: number): Observable<User> {
    return this.http.get('http://myapi/users/' + id)
             .map(response => response.json());
}

In situations where a Promise is required:

getUserDetails(id: number): Promise<User> {
    return this.http.get('http://myapi/users/' + id)
        .map(response => response.json())
        .toPromise();
}

Answer 8

For my project, I've opted to utilize Observables instead of Promises in my code. Here is an example:

getUserDetails(id: number): Observable<User> {
    return this.http.get('http://myapi/users/' + id)
             .map(response => response.json());
}

In situations where a Promise is required:

getUserDetails(id: number): Promise<User> {
    return this.http.get('http://myapi/users/' + id)
        .map(response => response.json())
        .toPromise();
}

Ways to dynamically link a JSON response object to an entity?

Answer №1

Answer №2

Answer №3

Answer №4

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