feat: pass deletePrefix and delete spread through dedupe (#319)

Author: ForbesLindesay

docs/dataloader.md

@@ -349,6 +349,45 @@ function onUserChanged(id: DbUser['id']) {
 }
 ```
 
+One downside of this approach is that you can only use this outside of a transaction. The simplest way to resolve this is to separate the implementation from the caching:
+
+```typescript
+import {dedupeAsync} from '@databases/dataloader';
+import database, {tables, DbUser} from './database';
+
+async function getUserBase(
+  database: Queryable,
+  userId: DbUser['id'],
+): Promise<DbUser> {
+  return await tables.users(database).findOneRequired({id: userId});
+}
+
+// (userId: DbUser['id']) => Promise<DbUser>
+const getUserCached = dedupeAsync<DbUser['id'], DbUser>(
+  async (userId) => await getUserBase(userId, database),
+  {cache: createCache({name: 'Users'})},
+);
+
+export async function getUser(
+  db: Queryable,
+  userId: DbUser['id'],
+): Promise<DbUser> {
+  if (db === database) {
+    // If we're using the default connection,
+    // it's safe to read from the cache
+    return await getUserCached(userId);
+  } else {
+    // If we're inside a transaction, we may
+    // need to bypass the cache
+    return await getUserBase(db, userId);
+  }
+}
+
+function onUserChanged(id: DbUser['id']) {
+  getUserCached.cache.delete(id);
+}
+```
+
 #### Caching fetch requests
 
 The following example caches requests to load a user from some imaginary API.

packages/cache/src/index.ts

@@ -442,7 +442,7 @@ export default function createCacheRealm(
           }
           this._delete(k);
         }
-        if (onReplicationEvent) {
+        if (onReplicationEvent && serializedKeys.size) {
           onReplicationEvent({
             kind: 'DELETE_MULTIPLE',
             name: this.name,

packages/dataloader/src/CacheMapImplementation.ts

@@ -0,0 +1,112 @@
+import {AsyncCacheMap, CacheMap, CacheMapInput, KeyPrefix} from './types';
+
+const supportsDeleteSpreadCache = new WeakMap<Function, boolean>();
+
+function supportsDeleteSpreadUncached<TKey, TValue>(
+  cacheMap: CacheMapInput<TKey, TValue>,
+): boolean {
+  return /^[^={]*\.\.\./.test(cacheMap.delete.toString());
+}
+
+function supportsDeleteSpread<TKey, TValue>(
+  cacheMap: CacheMapInput<TKey, TValue>,
+): boolean {
+  if (cacheMap.constructor === Map || cacheMap.constructor === WeakMap) {
+    return false;
+  }
+  if (cacheMap.constructor === Object || cacheMap.constructor === Function) {
+    return supportsDeleteSpreadUncached(cacheMap);
+  }
+
+  const cached = supportsDeleteSpreadCache.get(cacheMap.constructor);
+  if (cached !== undefined) return cached;
+
+  const freshValue = supportsDeleteSpreadUncached(cacheMap);
+  supportsDeleteSpreadCache.set(cacheMap.constructor, freshValue);
+  return freshValue;
+}
+
+class CacheMapImplementation<TKey, TResult, TMappedKey>
+  implements CacheMap<TKey, TResult>
+{
+  private readonly _map: CacheMapInput<TMappedKey, TResult>;
+  private readonly _mapKey: (key: TKey) => TMappedKey;
+  private readonly _supportsDeleteSpread: boolean;
+  constructor(
+    map: CacheMapInput<TMappedKey, TResult>,
+    mapKey: (key: TKey) => TMappedKey,
+  ) {
+    this._map = map;
+    this._mapKey = mapKey;
+    this._supportsDeleteSpread = supportsDeleteSpread(map);
+  }
+
+  get size() {
+    return this._map.size;
+  }
+  get(key: TKey): TResult | undefined {
+    const cacheKey = this._mapKey(key);
+    return this._map.get(cacheKey);
+  }
+  set(key: TKey, value: TResult): void {
+    const cacheKey = this._mapKey(key);
+    this._map.set(cacheKey, value);
+  }
+  deletePrefix(prefix: KeyPrefix<TKey>): void {
+    if (this._map.deletePrefix) {
+      this._map.deletePrefix(prefix as any);
+    } else if (this._map.keys && typeof prefix === 'string') {
+      for (const key of this._map.keys()) {
+        const k: unknown = key;
+        if (typeof k !== 'string') {
+          throw new Error(
+            `This cache contains non-string keys so you cannot use deletePrefix.`,
+          );
+        }
+        if (k.startsWith(prefix)) {
+          this._map.delete(key);
+        }
+      }
+    } else {
+      throw new Error(`This cache does not support deletePrefix.`);
+    }
+  }
+  delete(...keys: TKey[]): void {
+    if (!this._supportsDeleteSpread || keys.length < 2) {
+      for (const key of keys) {
+        const cacheKey = this._mapKey(key);
+        this._map.delete(cacheKey);
+      }
+    } else {
+      const cacheKeys = keys.map(this._mapKey);
+      this._map.delete(...cacheKeys);
+    }
+  }
+  clear(): void {
+    if (!this._map.clear) {
+      throw new Error(`This cache does not support clearing`);
+    }
+    this._map.clear();
+  }
+}
+export function createCacheMap<TKey, TValue, TMappedKey = TKey>(
+  map: CacheMapInput<TMappedKey, TValue>,
+  mapKey: (key: TKey) => TMappedKey,
+): CacheMap<TKey, TValue> {
+  return new CacheMapImplementation(map, mapKey);
+}
+
+class AsyncCacheMapImplementation<TKey, TResult, TMappedKey>
+  extends CacheMapImplementation<TKey, Promise<TResult>, TMappedKey>
+  implements AsyncCacheMap<TKey, TResult>
+{
+  set(key: TKey, value: TResult | Promise<TResult>): void {
+    super.set(key, Promise.resolve(value));
+  }
+}
+export function createAsyncCacheMap<TKey, TValue, TMappedKey = TKey>(
+  map: CacheMapInput<TMappedKey, Promise<TValue>>,
+  mapKey: (key: TKey) => TMappedKey,
+): AsyncCacheMap<TKey, TValue> {
+  return new AsyncCacheMapImplementation(map, mapKey);
+}

packages/dataloader/src/MultiKeyMap.ts

@@ -1,18 +1,10 @@
-import {CacheMap, CacheMapInput} from './types';
+import {CacheMapInput, Path, SubPath} from './types';
 
-type Path = readonly [unknown, ...(readonly unknown[])];
-type SubPath<TKeys extends readonly unknown[]> = TKeys extends readonly [
-  ...infer THead,
-  infer TTail,
-]
-  ? {readonly [i in keyof TKeys]: TKeys[i]} | SubPath<THead>
-  : never;
-
-export interface MultiKeyMap<TKeys extends Path, TValue>
-  extends CacheMap<TKeys, TValue> {
+export interface MultiKeyMap<TKeys extends Path, TValue> {
   readonly size: number;
   get: (key: TKeys) => TValue | undefined;
   set: (key: TKeys, value: TValue) => void;
+  deletePrefix: (key: SubPath<TKeys>) => void;
   delete: (key: TKeys | SubPath<TKeys>) => void;
   clear: () => void;
 }
@@ -136,6 +128,9 @@ class MultiKeyMapImplementation<TKeys extends Path, TValue, TMappedKey>
   set(key: TKeys, value: TValue): void {
     this._root.set(key, value);
   }
+  deletePrefix(key: SubPath<TKeys>): void {
+    this._root.delete(key);
+  }
   delete(key: TKeys | SubPath<TKeys>): void {
     this._root.delete(key);
   }