理解工厂模式

Node.js

1// Simulated client implementations
2class SqliteClient {
3  constructor(config) {
4    this.name = 'SQLite';
5    this.file = config.dbFile || 'dev.db';
6  }
7
8  connect() {
9    console.log(`Connecting to SQLite at ${this.file}`);
10  }
11}
12
13class PostgresClient {
14  constructor(config) {
15    this.name = 'PostgreSQL';
16    this.host = config.dbHost || 'localhost';
17  }
18
19  connect() {
20    console.log(`Connecting to PostgreSQL at ${this.host}`);
21  }
22}
23
24// Map environment to the correct client class
25const clientMap = {
26  development: SqliteClient,
27  production: PostgresClient,
28};
29
30// Factory function returns the correct client based on config
31function createDatabaseClient(config) {
32  const Client = clientMap[config.env];
33  if (!Client) throw new Error(`Unsupported environment: ${config.env}`);
34  return new Client(config);
35}
36
37// Usage
38const devConfig = { env: 'development', dbFile: 'test.db' };
39const devClient = createDatabaseClient(devConfig);
40devClient.connect();
41
42const prodConfig = { env: 'production', dbHost: 'prod.db.internal' };
43const prodClient = createDatabaseClient(prodConfig);
44prodClient.connect();

TypeScript

1interface Config {
2  env: string;
3  dbFile?: string;
4  dbHost?: string;
5}
6
7interface DatabaseClient {
8  connect(): void;
9}
10
11class SqliteClient implements DatabaseClient {
12  constructor(private config: Config) {}
13  connect() {
14    console.log(`Connecting to SQLite at ${this.config.dbFile || 'dev.db'}`);
15  }
16}
17
18class PostgresClient implements DatabaseClient {
19  constructor(private config: Config) {}
20  connect() {
21    console.log(`Connecting to PostgreSQL at ${this.config.dbHost || 'localhost'}`);
22  }
23}
24
25// Map-based declarative factory
26const clientMap: Record<string, new (config: Config) => DatabaseClient> = {
27  development: SqliteClient,
28  production: PostgresClient,
29};
30
31function createDatabaseClient(config: Config): DatabaseClient {
32  const Client = clientMap[config.env];
33  if (!Client) throw new Error(`Unsupported environment: ${config.env}`);
34  return new Client(config);
35}
36
37// Usage
38const devConfig: Config = { env: 'development', dbFile: 'test.db' };
39const devClient = createDatabaseClient(devConfig);
40devClient.connect();
41
42const prodConfig: Config = { env: 'production', dbHost: 'prod.db.internal' };
43const prodClient = createDatabaseClient(prodConfig);
44prodClient.connect();