関数のオーバーロードをTypescriptでやってみた～SQLにおけるunnest関数の実装を通して～
こんにちわ。nap5です。
SQLにおけるunnest関数の実装を通して関数のオーバーロードをTypescriptでやってみましたので、紹介です。
関数のオーバーロードについては以下にまとまっています。
inferで頑張るのがしんどくなってきたときには重宝しそうです。
また、アロー関数にはオーバーロードの構文がデフォではないので、いわゆる関数で実現していくのが、よさそうです。
unnestのイメージは以下を参考にしました。
定義側です
import { ArrayPath } from "dot-path-value";
import { omit } from "radash";
import type { Simplify } from "type-fest";
type ArrayElement<T> = T extends (infer U)[] ? U : never;
// オーバーロードのシグネチャ1: alias が指定された場合
export function unnest<T extends Record<string, unknown>, K extends ArrayPath<T> | keyof T, A extends string>(
data: T[],
arrayKey: K,
alias: A
): Simplify<Omit<T, K> & { [P in A]: ArrayElement<T[K]> }>[];
// オーバーロードのシグネチャ2: alias が指定されない場合
export function unnest<T extends Record<string, unknown>, K extends ArrayPath<T> | keyof T>(
data: T[],
arrayKey: K
): Simplify<Omit<T, K> & { [P in K]: ArrayElement<T[K]> }>[];
// 関数の実装
export function unnest<T extends Record<string, unknown>, K extends ArrayPath<T> | keyof T, A extends string>(
data: T[],
arrayKey: K,
alias?: A
) {
const result: (Omit<T, K> & { [key: string]: ArrayElement<T[K]> })[] = [];
data.forEach((item) => {
const arrayData = item[arrayKey] as Array<ArrayElement<T[K]>>;
arrayData.forEach((subItem) => {
const clonedItem: Omit<T, K> & { [key: string]: ArrayElement<T[K]> } = {
...omit(item, [arrayKey]),
[alias ?? arrayKey]: subItem,
};
result.push(clonedItem);
});
});
return result;
};
// 関数オーバーロードを使用すると、関数の実装部分で any を使用していても、オーバーロードのシグネチャで指定された型情報が呼び出し側に適用される
export function unstable_unnest<T extends Record<string, unknown>, K extends ArrayPath<T>, A extends string>(
data: T[],
arrayKey: K,
alias?: A
): any[] {
const result: any[] = [];
data.forEach((item) => {
const arrayData = item[arrayKey] as Record<string, unknown>[];
arrayData.forEach((subItem) => {
const clonedItem = {
...omit(item, [arrayKey]),
[alias ?? arrayKey]: subItem,
};
result.push(clonedItem);
});
});
return result;
};
使用側です
import { describe, test, expect } from "vitest";
import { unnest } from "@/index";
describe("unnest", () => {
test("Some data", () => {
type Person = {
id: number;
name: string;
roles: ("owner" | "member" | "admin")[];
};
const data: Person[] = [
{
id: 1,
name: "John",
roles: [
"admin",
"owner"
],
},
{
id: 2,
name: "Jane",
roles: [
"admin",
"owner",
"member"
],
},
];
const result = unnest(data, "roles", "role");
expect(result).toStrictEqual([
{ id: 1, name: "John", role: "admin" },
{ id: 1, name: "John", role: "owner" },
{ id: 2, name: "Jane", role: "admin" },
{ id: 2, name: "Jane", role: "owner" },
{ id: 2, name: "Jane", role: "member" },
]);
});
test("Person data", () => {
type Person = {
id: number;
name: string;
hobbies: { id: number; name: string }[];
};
const data: Person[] = [
{
id: 1,
name: "John",
hobbies: [
{ id: 1, name: "reading" },
{ id: 2, name: "gaming" },
],
},
{
id: 2,
name: "Jane",
hobbies: [
{ id: 3, name: "hiking" },
{ id: 4, name: "cooking" },
{ id: 5, name: "swimming" },
],
},
];
const result = unnest(data, "hobbies", "hobby");
expect(result).toStrictEqual([
{ id: 1, name: "John", hobby: { id: 1, name: "reading" } },
{ id: 1, name: "John", hobby: { id: 2, name: "gaming" } },
{ id: 2, name: "Jane", hobby: { id: 3, name: "hiking" } },
{ id: 2, name: "Jane", hobby: { id: 4, name: "cooking" } },
{ id: 2, name: "Jane", hobby: { id: 5, name: "swimming" } },
]);
});
test("Classroom data", () => {
type Student = {
id: number;
name: string;
};
type Classroom = {
id: number;
subject: string;
students: Student[];
};
const data: Classroom[] = [
{
id: 1,
subject: "Mathematics",
students: [
{ id: 1, name: "Alice" },
{ id: 2, name: "Bob" },
],
},
{
id: 2,
subject: "History",
students: [
{ id: 3, name: "Charlie" },
{ id: 4, name: "Daisy" },
{ id: 5, name: "Edward" },
],
},
];
const result = unnest(data, "students", "student");
expect(result).toStrictEqual([
{ id: 1, subject: "Mathematics", student: { id: 1, name: "Alice" } },
{ id: 1, subject: "Mathematics", student: { id: 2, name: "Bob" } },
{ id: 2, subject: "History", student: { id: 3, name: "Charlie" } },
{ id: 2, subject: "History", student: { id: 4, name: "Daisy" } },
{ id: 2, subject: "History", student: { id: 5, name: "Edward" } },
]);
});
test("Classroom data non alias", () => {
type Student = {
id: number;
name: string;
};
type Classroom = {
id: number;
subject: string;
students: Student[];
};
const data: Classroom[] = [
{
id: 1,
subject: "Mathematics",
students: [
{ id: 1, name: "Alice" },
{ id: 2, name: "Bob" },
],
},
{
id: 2,
subject: "History",
students: [
{ id: 3, name: "Charlie" },
{ id: 4, name: "Daisy" },
{ id: 5, name: "Edward" },
],
},
];
const result = unnest(data, "students");
expect(result).toStrictEqual([
{ id: 1, subject: "Mathematics", students: { id: 1, name: "Alice" } },
{ id: 1, subject: "Mathematics", students: { id: 2, name: "Bob" } },
{ id: 2, subject: "History", students: { id: 3, name: "Charlie" } },
{ id: 2, subject: "History", students: { id: 4, name: "Daisy" } },
{ id: 2, subject: "History", students: { id: 5, name: "Edward" } },
]);
});
});
demo code.
簡単ですが、以上です。