What is the method for creating a type depending on the query projection?

Question

What is the method for creating a type depending on the query projection?

Is there a method in TypeScript for defining a dynamic type that can be based on projection parameters?

For example, when executing a database query or GraphQL request, you might have a function like this:

interface Person {
  id: string;
  firstName: string;
  lastName: string;
}

function getPeople(projection: (keyof Person)[]): Promise<Partial<Person>[]> {...}

If I call getPeople(['id', 'firstName']), the returned objects will not include lastName since it was excluded from the projection. Is there a way to indicate this at the type level, rather than using Partial<Person> which still allows access to uninitialized properties?

typescript typescript-typings

Answer 1

Answer №1

To solve this problem, the key is to modify the getPeople function to be generic so that it can specify the types of parameters in the return type. Here's a revised version of the code that should help you achieve your goal:

interface Individual {
  id: string;
  firstName: string;
  lastName: string;
}

type Details<P, keys extends keyof P> = {
  [property in keys]: P[property];
};

declare function getPeople<keys extends keyof Individual>(
  attributes: keys[]
): Promise<Array<Details<Individual, keys>>>;

Answer 2

To solve this problem, the key is to modify the getPeople function to be generic so that it can specify the types of parameters in the return type. Here's a revised version of the code that should help you achieve your goal:

interface Individual {
  id: string;
  firstName: string;
  lastName: string;
}

type Details<P, keys extends keyof P> = {
  [property in keys]: P[property];
};

declare function getPeople<keys extends keyof Individual>(
  attributes: keys[]
): Promise<Array<Details<Individual, keys>>>;

Answer 3

Answer №2

Simply follow these instructions

To achieve this, use the following function:
function getPeople<K extends keyof Person>(projection: K[]):
Promise<Pick<Person, K>[]>

Answer 4

Simply follow these instructions

To achieve this, use the following function:
function getPeople<K extends keyof Person>(projection: K[]):
Promise<Pick<Person, K>[]>

Answer 5

Answer №3

interface TypeOfEntity {
  x: string;
  y: string;
  z: string;
}

const EntityItem: TypeOfEntity = { x: 'a', y: 'b', z: 'c' };

function EntityFilter<E extends keyof TypeOfEntity>(filter?: Array<E>): Pick<TypeOfEntity, E> {
  return EntityItem;
}

function execute() {
  const result = EntityFilter(['x']);
  
  result.y // will throw an error
}

Answer 6

interface TypeOfEntity {
  x: string;
  y: string;
  z: string;
}

const EntityItem: TypeOfEntity = { x: 'a', y: 'b', z: 'c' };

function EntityFilter<E extends keyof TypeOfEntity>(filter?: Array<E>): Pick<TypeOfEntity, E> {
  return EntityItem;
}

function execute() {
  const result = EntityFilter(['x']);
  
  result.y // will throw an error
}

Answer 7

Answer №4

If you want to make properties optional, simply add a question mark ? after the property name.

 interface Person {
      id: string;
      firstName?: string;
      lastName?: string;
    }

   function retrievePeople(projection: (keyof Person)[]): Promise<Partial<Person>[]> 
   {...}

By using the ? key, all properties except for id are now optional.

Answer 8

If you want to make properties optional, simply add a question mark ? after the property name.

 interface Person {
      id: string;
      firstName?: string;
      lastName?: string;
    }

   function retrievePeople(projection: (keyof Person)[]): Promise<Partial<Person>[]> 
   {...}

By using the ? key, all properties except for id are now optional.

What is the method for creating a type depending on the query projection?

Answer №1

Answer №2

Answer №3

Answer №4

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