What is the best way to implement an Interface in a HTTP response?

Question

What is the best way to implement an Interface in a HTTP response?

When working with my app, I receive a response from an API that follows a specific pattern.

export interface IApiResponseBody<T = any> {
    Error?: string;
    Message?: string;
    RowsAffected?: number;
    Success?: boolean;
    Data?: T;
    RowCount?: number;
}

I have no trouble assigning the interface to the response and accessing its elements. However, I encounter an issue when trying to assign an interface to the Data property using T.

let myData: IApiResponseBody<IPerson>  = {
    Success: true,
    Error: "",
    Message: "",
    RowsAffected: 9,
    Data: [{name: 'Steve', age: 26, gender : 'male'},
            {name: 'Susan', age: 21, gender : 'female'},
            {name: 'SteveFrank', age: 29, gender : 'male'}]}

An error occurs whether I use an array in the Data property or a simple document.

TSError: ⨯ Unable to compile TypeScript: index.ts:9:5 - error TS2559: Type '{ name: string; age: number; gender: string; }[]' has no properties in common with type 'IPerson'.

9 Data: [{name: 'Steve', age: 26, gender : 'male'}, ~~~~

How can I apply an interface to my Data element, whether it's an array of documents or a single document?

You can view the code on Repl.it by following this link:

Sample Playground

angular typescript

Answer 1

Answer №1

give this a shot:

export interface IResponsePayload<R = any> {
    FailureMsg?: string;
    AlertMsg?: string;
    RowsChanged?: number;
    WasSuccessful?: boolean;
    [attribute: string]?: R | R[];
    NumberOfRows?: number;
}

also, you can use:

let dataModel: IResponsePayload<IPersonnel>  = {
    WasSuccessful: true,
    FailureMsg: "",
    AlertMsg: "",
    RowsChanged: 9,
    Data: [{name: 'Samantha', age: 35, gender : 'female'}] // or {name: 'Samantha', age: 35, gender : 'female'}
    }

Answer 2

give this a shot:

export interface IResponsePayload<R = any> {
    FailureMsg?: string;
    AlertMsg?: string;
    RowsChanged?: number;
    WasSuccessful?: boolean;
    [attribute: string]?: R | R[];
    NumberOfRows?: number;
}

also, you can use:

let dataModel: IResponsePayload<IPersonnel>  = {
    WasSuccessful: true,
    FailureMsg: "",
    AlertMsg: "",
    RowsChanged: 9,
    Data: [{name: 'Samantha', age: 35, gender : 'female'}] // or {name: 'Samantha', age: 35, gender : 'female'}
    }

Answer 3

Answer №2

Data? must be of type T in an Array format, or if you prefer to allow either an Array or a single Object, utilize a union.

export interface IApiResponseBody<T = any> {
  Error?: string;
  Message?: string;
  RowsAffected?: number;
  Success?: boolean;
  Data?: T | T[];
  RowCount?: number;
}

export interface IPerson {
  name?: string;
  gender?: string;
  age?: number;
}

This setup now enables you to:

let myData: IApiResponseBody<IPerson> = {
  Success: true,
  Error: "",
  Message: "",
  RowsAffected: 9,
  Data: [
    {name: 'Steve', age: 26, gender: 'male'},
    {name: 'Susan', age: 21, gender: 'female'},
    {name: 'SteveFrank', age: 29, gender: 'male'}
  ]
}

or:

let myData: IApiResponseBody<IPerson> = {
  Success: true,
  Error: "",
  Message: "",
  RowsAffected: 9,
  Data: {name: 'Steve', age: 26, gender: 'male'}
}

Answer 4

Data? must be of type T in an Array format, or if you prefer to allow either an Array or a single Object, utilize a union.

export interface IApiResponseBody<T = any> {
  Error?: string;
  Message?: string;
  RowsAffected?: number;
  Success?: boolean;
  Data?: T | T[];
  RowCount?: number;
}

export interface IPerson {
  name?: string;
  gender?: string;
  age?: number;
}

This setup now enables you to:

let myData: IApiResponseBody<IPerson> = {
  Success: true,
  Error: "",
  Message: "",
  RowsAffected: 9,
  Data: [
    {name: 'Steve', age: 26, gender: 'male'},
    {name: 'Susan', age: 21, gender: 'female'},
    {name: 'SteveFrank', age: 29, gender: 'male'}
  ]
}

or:

let myData: IApiResponseBody<IPerson> = {
  Success: true,
  Error: "",
  Message: "",
  RowsAffected: 9,
  Data: {name: 'Steve', age: 26, gender: 'male'}
}

Answer 5

Answer №3

When you attempt to access data that may not exist, the error occurs because of how the data is structured. The shorthand notation T[] actually represents either a value of T[] or undefined within the Data object.

So when trying to retrieve a property like myData.data[0].name, it could potentially result in accessing a non-existent value (undefined), leading to an error being thrown.

Possible Solutions:

One solution is to first check if the data exists before attempting to access it:

if (myData.Data) {
  console.log(myData.Data[0].name)
}

Another approach would be to ensure that there is always data present by removing the '?' character from the interface definition:

export interface IApiResponseBody<T = any> {
  Error?: string;
  Message?: string;
  RowsAffected?: number;
  Success?: boolean;
  Data: T[];
  RowCount?: number;
}

For a live example and demonstration of these solutions, visit: Repl.it

Answer 6

When you attempt to access data that may not exist, the error occurs because of how the data is structured. The shorthand notation T[] actually represents either a value of T[] or undefined within the Data object.

So when trying to retrieve a property like myData.data[0].name, it could potentially result in accessing a non-existent value (undefined), leading to an error being thrown.

Possible Solutions:

One solution is to first check if the data exists before attempting to access it:

if (myData.Data) {
  console.log(myData.Data[0].name)
}

Another approach would be to ensure that there is always data present by removing the '?' character from the interface definition:

export interface IApiResponseBody<T = any> {
  Error?: string;
  Message?: string;
  RowsAffected?: number;
  Success?: boolean;
  Data: T[];
  RowCount?: number;
}

For a live example and demonstration of these solutions, visit: Repl.it

What is the best way to implement an Interface in a HTTP response?

Answer №1

Answer №2

Answer №3

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