Ensure that the key of an object's property is identical to the value of the property

Question

Ensure that the key of an object's property is identical to the value of the property

I am tasked with creating a specific object structure, where each object key must match its corresponding ID:

const entities = {
  abc: {
    id: 'abc'
  },
  def: {
    id: 'def'
  }
}

To achieve this, I attempted the following code:

interface EntitiesMap<E extends Entity> {
  [K in E['id']]: E;
}

interface Entity {
  id: string;
}

However, this code does not guarantee that the object key and ID value will match. In the example below, 'ghi' should throw an error as it doesn't match 'aaaaa':

const entities = {
  ghi: {
    id: 'aaaaa'
  }
}

Does anyone have suggestions on how to ensure the proper matching of keys and IDs?

typescript

Answer 1

Answer №1

To establish a clear understanding, it is crucial to define a specific type and always be mindful of the keys involved.

type Entity<T extends keyof any> = {
  [K in T]: {
    id: K;
  };
};

const entities: Entity<'abc' | 'def' | 'def2' | 'def3'> = {
  abc: {
    id: 'abc'
  },
  def: {
    id: 'def'
  },
  def2: {
    id: 'abc' // <- fails
  },
  def3: {
    id: 'def4' // <- fails
  },
}

To manage keys effectively, consider utilizing a helper function, although its appropriateness may vary.

const validateEntities = <K extends keyof any>(value: Entity<K>): Entity<K> => {
  return value;
};

const entities = validateEntities({
  abc: {
    id: 'abc'
  },
  def: {
    id: 'def'
  },
  def2: {
    id: 'abc' // <- fails
  },
  def3: {
    id: 'def4' // <- fails
  },
});

Answer 2

To establish a clear understanding, it is crucial to define a specific type and always be mindful of the keys involved.

type Entity<T extends keyof any> = {
  [K in T]: {
    id: K;
  };
};

const entities: Entity<'abc' | 'def' | 'def2' | 'def3'> = {
  abc: {
    id: 'abc'
  },
  def: {
    id: 'def'
  },
  def2: {
    id: 'abc' // <- fails
  },
  def3: {
    id: 'def4' // <- fails
  },
}

To manage keys effectively, consider utilizing a helper function, although its appropriateness may vary.

const validateEntities = <K extends keyof any>(value: Entity<K>): Entity<K> => {
  return value;
};

const entities = validateEntities({
  abc: {
    id: 'abc'
  },
  def: {
    id: 'def'
  },
  def2: {
    id: 'abc' // <- fails
  },
  def3: {
    id: 'def4' // <- fails
  },
});

Answer 3

Answer №2

That's because you specified id as a string and 'aaaaa' is indeed a string. A more specific way to define id could be like this:

type IdType = keyof typeof entities // "abc" | "def"

// This allows you to use IdType as the type for id

interface Entity {
  id: IdType
}

This may not be exactly what you were looking for, but it's a good starting point. Hopefully, it will be helpful to you.

Answer 4

That's because you specified id as a string and 'aaaaa' is indeed a string. A more specific way to define id could be like this:

type IdType = keyof typeof entities // "abc" | "def"

// This allows you to use IdType as the type for id

interface Entity {
  id: IdType
}

This may not be exactly what you were looking for, but it's a good starting point. Hopefully, it will be helpful to you.

Answer 5

Answer №3

If you're fine with utilizing the identity function to generate the entities, you have the option to employ generics for inferring the root keys and mapped types to validate the values of the nested objects:

const createEntities = <TKeys extends string>(entities: { [K in TKeys]: { id: K } }) => entities;

// All good
const entities = createEntities({
  abc: {
    id: 'abc'
  },
  def: {
    id: 'def'
  }
})

// Error: type '"aaaaa"' is not compatible with type '"ghi"'
createEntities({
  ghi: {
    id: 'aaaaa'
  }
})

Try it out on Playground

Answer 6

If you're fine with utilizing the identity function to generate the entities, you have the option to employ generics for inferring the root keys and mapped types to validate the values of the nested objects:

const createEntities = <TKeys extends string>(entities: { [K in TKeys]: { id: K } }) => entities;

// All good
const entities = createEntities({
  abc: {
    id: 'abc'
  },
  def: {
    id: 'def'
  }
})

// Error: type '"aaaaa"' is not compatible with type '"ghi"'
createEntities({
  ghi: {
    id: 'aaaaa'
  }
})

Try it out on Playground

Answer 7

Answer №4

By utilizing a type signature that includes as const when declaring entities, it becomes possible to achieve the desired outcome purely at the type level, without the need for any JavaScript functions:

type ValidEntities<E> = {[K in keyof E]: {id: K}}
type IsValid<E extends ValidEntities<E>> = true // Can be any type

// Successfully validated entities
const entities = {
  abc: {
    fine: 3,
    id: 'abc'
  },
  def: {
    id: 'def'
  }
} as const

type Validate = IsValid<typeof entities>

If the entities structure is invalid, a type error will be triggered at IsValid<typeof entities>.

Explore in TypeScript playground

Answer 8

By utilizing a type signature that includes as const when declaring entities, it becomes possible to achieve the desired outcome purely at the type level, without the need for any JavaScript functions:

type ValidEntities<E> = {[K in keyof E]: {id: K}}
type IsValid<E extends ValidEntities<E>> = true // Can be any type

// Successfully validated entities
const entities = {
  abc: {
    fine: 3,
    id: 'abc'
  },
  def: {
    id: 'def'
  }
} as const

type Validate = IsValid<typeof entities>

If the entities structure is invalid, a type error will be triggered at IsValid<typeof entities>.

Explore in TypeScript playground

Ensure that the key of an object's property is identical to the value of the property

Answer №1

Answer №2

Answer №3

Answer №4

Similar questions

Navigating the terrain of multiple checkboxes in React and gathering all the checked boxes

Guide to upgrading ag-grid-community from 20.1.0 to 24.1.0

Decipher and comprehend the buttons listed in the language translation document

In TypeScript, this regular expression dialect does not permit the use of category shorthand

Jest is having difficulty locating a module while working with Next.js, resulting in

Error: 'next' is not defined in the beforeRouteUpdate method

Is there a method to implement retries for inconsistent tests with jest-puppeteer?

How can we effectively test arrow functions in unit tests for Angular development?

Using the input type 'number' will result in null values instead of characters

How to override or redefine a TypeScript class with generics

How to transform a file into a uInt8Array using Angular

Unlock the Power of EmailJS with Vue.js 2 and TypeScript

Using TypeScript with Angular-UI Modals

Issue with Angular ngFor within a particular dialog window?

The object literal's property 'children' is assumed to have a type of 'any[]' by default

Organizing Telephone Number Entries in Angular

Load the workspace's current state when opening a VS Code extension

What is the process for exporting a class and declaring middleware in TypeScript?

`Mapping child routes in Angular using basic components`

Unable to loop through the "dataList" retrieved from a service call to the java backend within an Angular 9 application