Hari 20: Type-Safe Builder Pattern

Builder Pattern dengan TypeScript

type BuildState = Record;

class QueryBuilder<
    T extends string,
    Set extends Partial> = {}
> {
    private config: Record = {};

    select(fields: string[]): QueryBuilder> {
        this.config.select = fields;
        return this as any;
    }

    from(table: string): QueryBuilder> {
        this.config.from = table;
        return this as any;
    }

    where(condition: string): QueryBuilder {
        this.config.where = condition;
        return this;
    }

    // build hanya tersedia jika select & from sudah di-set
    build(this: QueryBuilder>): string {
        const { select, from, where } = this.config;
        let q = `SELECT ${select.join(", ")} FROM ${from}`;
        if (where) q += ` WHERE ${where}`;
        return q;
    }
}

const query = new QueryBuilder()
    .from("users")
    .select(["id", "nama", "email"])
    .where("aktif = true")
    .build();

console.log(query);