Database Integration with TypeScript

TypeScript database integrations range from raw SQL drivers to query builders and ORMs. Make queries parameterized, close connections, and define transaction boundaries. Database result types describe expectations but do not prove that remote data matches. This standalone lesson models a repository; use an appropriate Node.js SQL driver or ORM when connecting to a real database.

The repository interface returns a Promise of a task or undefined. Business logic can consume that contract while a SQL-backed implementation handles connection and query details separately.

Writing WHERE id = ${userInput} inside SQL strings risks injection; parameterize values with the database driver's API.

This source was compiled using TypeScript 5.8.3 with strict checking, then executed with Node.js 22.16.0. Its stdout below is the actual captured output. The core logic is runnable without a framework or a remote API; integration-specific examples appear in a separate lab when needed.

TypeScript source

type Task = { id: number; title: string; done: boolean };
interface TaskRepository { get(id: number): Promise<Task | undefined> }
class MemoryRepository implements TaskRepository {
  constructor(private readonly tasks: Task[]) {}
  async get(id: number): Promise<Task | undefined> {
    return this.tasks.find(task => task.id === id);
  }
}
async function main(): Promise<void> {
  const repo = new MemoryRepository([{ id: 1, title: "Review", done: false }]);
  console.log(await repo.get(1));
}
main().catch(console.error);

Verified output

{ id: 1, title: 'Review', done: false }

Compile: npx tsc --strict --target es2022 --module commonjs database-integration.ts; run: node database-integration.js. For examples importing node: modules, install @types/node as a development dependency; for browser or React projects use the separate lab setup.

The repository interface returns a Promise of a task or undefined. Business logic can consume that contract while a SQL-backed implementation handles connection and query details separately.

Before editing the code, predict what the output will be for one changed input. Run it and compare your prediction with the actual result.

Writing WHERE id = ${userInput} inside SQL strings risks injection; parameterize values with the database driver's API.

Determine whether the issue belongs to the type system, a trust boundary, or actual runtime behavior before choosing a correction.

Design a table with a unique ID, then implement get(id) in a real Node database client using placeholders.

Record expected success and failure outcomes, run the code, and compare the observed behavior. Keep the exercise compatible with strict type checking.

The repository interface returns a Promise of a task or undefined. Business logic can consume that contract while a SQL-backed implementation handles connection and query details separately.

Apply the same reasoning to the practice task, then integrate it into a real app only when the runtime and dependency setup are ready.