使用 Typescript 泛型类型

Question

I have an interface that describes basic database CRUD operations like so:

export interface IUserDB {
  insert: (params: UserAttributes) => Promise<UserResult>
  findById: ({ id }: { id: number }) => Promise<UserResult | null>
  findByEmail: ({ email }: { email: string }) => Promise<UserResult | null>
  remove: ({ id }: { id: number }) => Promise<any>
  update: ({
    id,
    ...changes
  }: { id: number } & UserAttributes) => Promise<UserResult>
}

I then go ahead to use this interface in this manner:

const makeAddUser = ({ usersDb }: { usersDb: IUserDb }) => {
  return async function addUser(userDetails: User) {
    const user = makeUser(userDetails)
    const exists = await usersDb.findByEmail({ email: user.getEmail() })
    if (exists) {
      throw new UniqueConstraintError('Email')
    }
    const newUser = await usersDb.insert({
      name: user.getName(),
      email: user.getEmail(),
      password: user.getPassword(),
      username: user.getUsername(),
    })

    const { id } = newUser.user
    await publisher(id.toString(), 'newuser.verify')
    await consumer('verify_queue', verifyUser, '*.verify')
    return newUser
  }
}

I want to be able to reuse this interface for PostDb and CommentDb without me having to write another interface that describes a Post database operation, how can I achieve this? I read about Typescript Generics , but I am not really sure how to apply it to this case, any help will be appreciated. I am still trying to get a hang of Typescript. Thank you very much!

Answer 1

Not really sure how to explain it other than to just show you, but here is what I would do (with some filler code to make things work, but just focus on the interfaces). But basically you define an interface, and pass in the types you want it to support inside <>. So below I do

export interface IDB<Attributes, Result> {

which means you pass in two additional types to this:

interface IUserDb extends IDB<UserAttributes, UserResult>

and now IUserDb is an IDB where any place IDB has Attributes it instead uses UserAttributes , and same with Result and UserResult :

https://codesandbox.io/s/typescript-playground-export-forked-nej0s?file=/index.ts:0-1569

 export interface IDB<Attributes, Result> { insert: (params: Omit<Attributes, 'id'>) => Promise<Result> findById: ({ id }: { id: number }) => Promise<Result | null> remove: ({ id }: { id: number }) => Promise<any> update: ({ id, ...changes }: { id: number } & Attributes) => Promise<Result> } interface UserAttributes { id: string; name: string; username: string; email: string; password: string; } interface UserResult extends UserAttributes { getEmail(): string getName(): string getPassword(): string getUsername(): string } export interface IUserDb extends IDB<UserAttributes, UserResult>{ findByEmail: ({ email }: { email: string }) => Promise<UserResult | null> } const makeUser = (user: UserAttributes): UserResult => { const u: any = {...user }; u.getName = () => u.name; u.getEmail = () => u.email; u.getPassword = () => u.password; u.getUsername = () => u.username; return u as UserResult; } const UniqueConstraintError = (err: string) => new Error(`Unique Constraint Error: ${err}`); const makeAddUser = ({ usersDb }: { usersDb: IUserDb }) => { return async function addUser(userDetails: UserAttributes) { const user = makeUser(userDetails) const exists = await usersDb.findByEmail({ email: user.getEmail() }) if (exists) { throw UniqueConstraintError('Email') } const newUser = await usersDb.insert({ name: user.getName(), email: user.getEmail(), password: user.getPassword(), username: user.getUsername(), }) return newUser } }