javascript - typescript 错误 : Type 'Document[]' is not assignable to custom type

Question

有一个简单的 nestJS 服务，它返回 mongoDb 查询的结果。如您所见，我尝试设置预期的结果类型，即文档数组。

class MyDataset {
    group: string
    location: string
    type: string
    reported: Date
}

async getDatasets(): Promise<Array<MyDataset>> {
    const Collection = this.db.collection('collection')
    const result = await Collection.find({}).toArray()
    return result // <-- ts error
} 

但是我确实得到了 TS 错误

Type 'Document[]' is not assignable to type 'MyDataset[]'.
Type 'Document' is missing the following properties from type 'MyDataset': group, location, type, reported

我不明白，我做错了什么。有人可以解释一下这个问题吗？

Answer 1

该错误表明您期望的 MyDataset 类型与 Collection.find({}).toArray() 返回的类型不匹配。 mongo 数据库文档说明 toArray()方法返回文档数组。

这复制了相同的行为:

type DocumentA = {
    group: string
    location: string
    type: string
    reported: Date
}

type DocumentB = {
    anotherField: string
}

const arrayOfDocumentsA = () => {
    const res: DocumentA[] = [];
    return res;
}

const arrayOfDocumentsB = () => {
    const res: DocumentB[] = [];
    return res;
}

const getDatasets = (): Array<DocumentA> => {
    return arrayOfDocumentsB(); // ts error
};

这会出现以下错误:

Type 'DocumentB[]' is not assignable to type 'DocumentA[]'.
  Type 'DocumentB' is missing the following properties from type 'DocumentA': group, location, type, reported ts(2322)