TypeScript：编写泛型函数匹配Collection类find方法重载签名问题

需求 #

编写一个泛型函数，匹配Collection类find方法的第二个重载签名：

find(filter: Filter<TSchema>, options?: FindOptions): FindCursor<WithId<TSchema>>;

现有代码 #

import { Document, Filter, FindCursor, FindOptions, MongoClient, WithId } from 'mongodb'; // tags: ^5.6.0

const uri = '<connection string uri>';
const client = new MongoClient(uri);

function findUsers<TSchema extends Document = Document>(
    find_pattern: Filter<TSchema>,
    options?: FindOptions,
): FindCursor<WithId<TSchema>> {
    return client.db('main').collection('accounts').find(find_pattern, options);
}

Collection类的find方法重载签名 #

export declare class Collection<TSchema extends Document = Document> {
    //...
    find(): FindCursor<WithId<TSchema>>;
    find(filter: Filter<TSchema>, options?: FindOptions): FindCursor<WithId<TSchema>>;
    find<T extends Document>(filter: Filter<TSchema>, options?: FindOptions): FindCursor<T>;
    //...
}

类型错误信息 #

1. return语句错误：

Type 'FindCursor<WithId<Document>>' is not assignable to type 'FindCursor<WithId<TSchema>>'.
  Type 'WithId<Document>' is not assignable to type 'WithId<TSchema>'.
    Type 'WithId<Document>' is not assignable to type 'EnhancedOmit<TSchema, "_id">'.(2322)

2. .find(find_pattern, options)调用错误：

No overload matches this call.
  Overload 1 of 3, '(filter: Filter<Document>, options?: FindOptions<Document> | undefined): FindCursor<WithId<Document>>', gave the following error.
    Argument of type 'Filter<TSchema>' is not assignable to parameter of type 'Filter<Document>'.
      Type 'Filter<TSchema>' is not assignable to type 'RootFilterOperators<WithId<Document>>'.
        Types of property '$and' are incompatible.
          Type 'Filter<WithId<TSchema>>[] | undefined' is not assignable to type 'Filter<WithId<Document>>[] | undefined'.
            Type 'Filter<WithId<TSchema>>[]' is not assignable to type 'Filter<WithId<Document>>[]'.
              Type 'Filter<WithId<TSchema>>' is not assignable to type 'Filter<WithId<Document>>'.
                Type 'Filter<WithId<TSchema>>' is not assignable to type 'RootFilterOperators<WithId<WithId<Document>>>'.
                  Types of property '$where' are incompatible.
                    Type 'string | ((this: WithId<WithId<TSchema>>) => boolean) | undefined' is not assignable to type 'string | ((this: WithId<WithId<Document>>) => boolean) | undefined'.
                      Type '(this: WithId<WithId<TSchema>>) => boolean' is not assignable to type 'string | ((this: WithId<WithId<Document>>) => boolean) | undefined'.
                        Type '(this: WithId<WithId<TSchema>>) => boolean' is not assignable to type '(this: WithId<WithId<Document>>) => boolean'.
                          The 'this' types of each signature are incompatible.
                            Type 'WithId<WithId<Document>>' is not assignable to ty

环境版本 #

"typescript": "^5.1.6",
"mongodb": "^5.6.0"

解决方案 #

问题根源在于调用collection('accounts')时未指定泛型类型，默认使用Document作为TSchema，导致后续find方法的类型推导与函数泛型参数TSchema不匹配。

修改代码，给collection指定泛型参数TSchema，让Collection实例的类型与函数泛型保持一致，即可正确匹配目标重载签名：

import { Document, Filter, FindCursor, FindOptions, MongoClient, WithId } from 'mongodb'; // tags: ^5.6.0

const uri = '<connection string uri>';
const client = new MongoClient(uri);

function findUsers<TSchema extends Document = Document>(
    find_pattern: Filter<TSchema>,
    options?: FindOptions,
): FindCursor<WithId<TSchema>> {
    // 给collection指定泛型TSchema
    return client.db('main').collection<TSchema>('accounts').find(find_pattern, options);
}

修改后，Collection实例的TSchema与函数泛型参数统一，find方法会正确匹配第二个重载签名，类型错误即可消除。

内容的提问来源于stack exchange，提问作者Lin Du