Generic repository pattern in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a generic repository interface.

Typescript

interface IRepository<T> {
  getById(id: number): [1];
}

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AT

Bnumber

Cvoid

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a fixed type like number or string instead of the generic type.

Using void as return type which means no value is returned.

The method getById returns an object of the generic type T.

2fill in blank

medium

Complete the code to define a generic method to add an item to the repository.

Typescript

interface IRepository<T> {
  add(item: [1]): void;
}

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Aany

Bobject

CT

Dunknown

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-generic type like any or object which loses type safety.

Using unknown which requires type assertions.

The add method accepts an item of the generic type T.

3fill in blank

hard

Fix the error in the generic repository class declaration.

Typescript

class Repository<[1]> implements IRepository<T> {
  private items: T[] = [];

  add(item: T): void {
    this.items.push(item);
  }

  getById(id: number): T | undefined {
    return this.items.find(item => (item as any).id === id);
  }
}

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AT

BU

CItem

DK

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different generic type parameter name than the interface.

Omitting the generic parameter in the class declaration.

The class must declare the generic type parameter T to match the interface.

4fill in blank

hard

Fill both blanks to create a generic repository method that returns all items matching a condition.

Typescript

class Repository<T> implements IRepository<T> {
  private items: T[] = [];

  findAll(predicate: (item: [1]) => boolean): [2] {
    return this.items.filter(predicate);
  }
}

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AT

BT[]

Cany

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using any instead of the generic type T.

Returning void instead of an array.

The predicate function takes an item of type T, and the method returns an array of T.

5fill in blank

hard

Fill all three blanks to implement a generic repository method that updates an item by id.

Typescript

class Repository<T extends { id: number }> implements IRepository<T> {
  private items: T[] = [];

  update(id: number, [1]: Partial<[2]>): boolean {
    const index = this.items.findIndex(item => item.id === id);
    if (index === -1) return false;
    this.items[index] = { ...this.items[index], ...[3] };
    return true;
  }
}

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Achanges

BT

Dupdates

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the changes parameter and spread variable.

Not using Partial type for changes.

The method takes changes of type Partial<T> and merges them into the existing item.