FirestoreDataConverter interface

withConverter() 使用的转换器,用于将 AppModelType 类型的用户对象转换为 DbModelType 类型的 Firestore 数据。

借助转换器,您可以在从 Firestore 存储和检索对象时指定泛型类型参数。

在这种情况下,“AppModel”是在应用中使用,用于将相关信息和功能打包在一起的类。例如,此类类可能包含复杂的嵌套数据类型、用于记忆的属性、Firestore 不支持的类型的属性(例如 symbolbigint),以及执行复合操作的辅助函数。此类类不适合和/或无法存储到 Firestore 数据库中。需要将此类类的实例转换为“普通的旧 JavaScript 对象”(POJO) 只具有完全基本的属性,可能嵌套在其他 POJO 或 POJO 数组中。在此上下文中,这种类型称为“DbModel”并且会是一个适合持久保存到 Firestore 的对象。为方便起见,应用可以实现 FirestoreDataConverter 并使用 Firestore 对象(例如 DocumentReferenceQuery)注册转换器,以便在存储到 Firestore 时自动将 AppModel 转换为 DbModel,并在从 Firestore 检索时将 DbModel 转换为 AppModel

签名

export declare interface FirestoreDataConverter<AppModelType, DbModelType extends DocumentData = DocumentData> 

方法

方法 说明
fromFirestore(快照) 由 Firestore SDK 调用,用于将 Firestore 数据转换为 AppModelType 类型的对象。您可以通过调用 snapshot.data() 来访问数据。通常,从 snapshot.data() 返回的数据可以转换为 DbModelType;但是,无法保证这一点,因为 Firestore 不会在数据库上强制执行架构。例如,从以前版本的应用写入或从不使用类型转换器的其他客户端写入,可能会写入具有不同属性和/或属性类型的数据。实现需要选择是从不符合要求的数据中正常恢复,还是抛出错误。
toFirestore(modelObject) 由 Firestore SDK 调用,用于将 AppModelType 类型的自定义模型对象转换为 DbModelType 类型的普通 JavaScript 对象(适合直接写入 Firestore 数据库)。与 setDoc() 和 . 一起使用。WithFieldValue<T> 类型扩展 T,以允许将 FieldValues(例如 deleteField())用作属性值。
toFirestore(modelObject, options) 由 Firestore SDK 调用,用于将 AppModelType 类型的自定义模型对象转换为 DbModelType 类型的普通 JavaScript 对象(适合直接写入 Firestore 数据库)。与 setDoc() 以及 merge:truemergeFields 结合使用。PartialWithFieldValue<T> 类型扩展 Partial<T>,以允许将 FieldValues(如 arrayUnion())用作属性值。它还通过允许省略嵌套字段来支持嵌套的 Partial

FirestoreDataConverter.fromFirestore()

由 Firestore SDK 调用,用于将 Firestore 数据转换为 AppModelType 类型的对象。您可以通过以下电话号码访问您的数据:snapshot.data()

通常,从 snapshot.data() 返回的数据可转换为 DbModelType;但是,无法保证这一点,因为 Firestore 不会在数据库上强制执行架构。例如,从以前版本的应用写入或从不使用类型转换器的其他客户端写入,可能会写入具有不同属性和/或属性类型的数据。实现需要选择是从不符合要求的数据中正常恢复,还是抛出错误。

签名

fromFirestore(snapshot: QueryDocumentSnapshot<DocumentData, DocumentData>): AppModelType;

参数

参数 类型 说明
快照 QueryDocumentSnapshot<DocumentDataDocumentData> 包含您的数据和元数据的 QueryDocumentSnapshot

返回

应用模型类型

FirestoreDataConverter.toFirestore()

由 Firestore SDK 调用,用于将 AppModelType 类型的自定义模型对象转换为 DbModelType 类型的普通 JavaScript 对象(适合直接写入 Firestore 数据库)。与 setDoc() 和 .

WithFieldValue<T> 类型扩展 T,以允许将 FieldValues(例如 deleteField())用作属性值。

签名

toFirestore(modelObject: WithFieldValue<AppModelType>): WithFieldValue<DbModelType>;

参数

参数 类型 说明
modelObject WithFieldValue<AppModelType>

返回

WithFieldValue<DbModelType>

FirestoreDataConverter.toFirestore()

由 Firestore SDK 调用,用于将 AppModelType 类型的自定义模型对象转换为 DbModelType 类型的普通 JavaScript 对象(适合直接写入 Firestore 数据库)。与 setDoc() 以及 merge:truemergeFields 结合使用。

PartialWithFieldValue<T> 类型扩展 Partial<T>,以允许将 FieldValues(如 arrayUnion())用作属性值。它还通过允许省略嵌套字段来支持嵌套的 Partial

签名

toFirestore(modelObject: PartialWithFieldValue<AppModelType>, options: SetOptions): PartialWithFieldValue<DbModelType>;

参数

参数 类型 说明
modelObject PartialWithFieldValue<AppModelType>
选项 SetOptions

返回

PartialWithFieldValue<DbModelType>

示例

简单示例

const numberConverter = {
    toFirestore(value: WithFieldValue<number>) {
        return { value };
    },
    fromFirestore(snapshot: QueryDocumentSnapshot, options: SnapshotOptions) {
        return snapshot.data(options).value as number;
    }
};

async function simpleDemo(db: Firestore): Promise<void> {
    const documentRef = doc(db, 'values/value123').withConverter(numberConverter);

    // converters are used with `setDoc`, `addDoc`, and `getDoc`
    await setDoc(documentRef, 42);
    const snapshot1 = await getDoc(documentRef);
    assertEqual(snapshot1.data(), 42);

    // converters are not used when writing data with `updateDoc`
    await updateDoc(documentRef, { value: 999 });
    const snapshot2 = await getDoc(documentRef);
    assertEqual(snapshot2.data(), 999);
}

高级示例

// The Post class is a model that is used by our application.
// This class may have properties and methods that are specific
// to our application execution, which do not need to be persisted
// to Firestore.
class Post {
    constructor(
        readonly title: string,
        readonly author: string,
        readonly lastUpdatedMillis: number
    ) {}
    toString(): string {
        return `${this.title} by ${this.author}`;
    }
}

// The PostDbModel represents how we want our posts to be stored
// in Firestore. This DbModel has different properties (`ttl`,
// `aut`, and `lut`) from the Post class we use in our application.
interface PostDbModel {
    ttl: string;
    aut: { firstName: string; lastName: string };
    lut: Timestamp;
}

// The `PostConverter` implements `FirestoreDataConverter` and specifies
// how the Firestore SDK can convert `Post` objects to `PostDbModel`
// objects and vice versa.
class PostConverter implements FirestoreDataConverter<Post, PostDbModel> {
    toFirestore(post: WithFieldValue<Post>): WithFieldValue<PostDbModel> {
        return {
            ttl: post.title,
            aut: this._autFromAuthor(post.author),
            lut: this._lutFromLastUpdatedMillis(post.lastUpdatedMillis)
        };
    }

    fromFirestore(snapshot: QueryDocumentSnapshot, options: SnapshotOptions): Post {
        const data = snapshot.data(options) as PostDbModel;
        const author = `${data.aut.firstName} ${data.aut.lastName}`;
        return new Post(data.ttl, author, data.lut.toMillis());
    }

    _autFromAuthor(
        author: string | FieldValue
    ): { firstName: string; lastName: string } | FieldValue {
        if (typeof author !== 'string') {
            // `author` is a FieldValue, so just return it.
            return author;
        }
        const [firstName, lastName] = author.split(' ');
        return {firstName, lastName};
    }

    _lutFromLastUpdatedMillis(
        lastUpdatedMillis: number | FieldValue
    ): Timestamp | FieldValue {
        if (typeof lastUpdatedMillis !== 'number') {
            // `lastUpdatedMillis` must be a FieldValue, so just return it.
            return lastUpdatedMillis;
        }
        return Timestamp.fromMillis(lastUpdatedMillis);
    }
}

async function advancedDemo(db: Firestore): Promise<void> {
    // Create a `DocumentReference` with a `FirestoreDataConverter`.
    const documentRef = doc(db, 'posts/post123').withConverter(new PostConverter());

    // The `data` argument specified to `setDoc()` is type checked by the
    // TypeScript compiler to be compatible with `Post`. Since the `data`
    // argument is typed as `WithFieldValue<Post>` rather than just `Post`,
    // this allows properties of the `data` argument to also be special
    // Firestore values that perform server-side mutations, such as
    // `arrayRemove()`, `deleteField()`, and `serverTimestamp()`.
    await setDoc(documentRef, {
        title: 'My Life',
        author: 'Foo Bar',
        lastUpdatedMillis: serverTimestamp()
    });

    // The TypeScript compiler will fail to compile if the `data` argument to
    // `setDoc()` is _not_ compatible with `WithFieldValue<Post>`. This
    // type checking prevents the caller from specifying objects with incorrect
    // properties or property values.
    // @ts-expect-error "Argument of type { ttl: string; } is not assignable
    // to parameter of type WithFieldValue<Post>"
    await setDoc(documentRef, { ttl: 'The Title' });

    // When retrieving a document with `getDoc()` the `DocumentSnapshot`
    // object's `data()` method returns a `Post`, rather than a generic object,
    // which would have been returned if the `DocumentReference` did _not_ have a
    // `FirestoreDataConverter` attached to it.
    const snapshot1: DocumentSnapshot<Post> = await getDoc(documentRef);
    const post1: Post = snapshot1.data()!;
    if (post1) {
        assertEqual(post1.title, 'My Life');
        assertEqual(post1.author, 'Foo Bar');
    }

    // The `data` argument specified to `updateDoc()` is type checked by the
    // TypeScript compiler to be compatible with `PostDbModel`. Note that
    // unlike `setDoc()`, whose `data` argument must be compatible with `Post`,
    // the `data` argument to `updateDoc()` must be compatible with
    // `PostDbModel`. Similar to `setDoc()`, since the `data` argument is typed
    // as `WithFieldValue<PostDbModel>` rather than just `PostDbModel`, this
    // allows properties of the `data` argument to also be those special
    // Firestore values, like `arrayRemove()`, `deleteField()`, and
    // `serverTimestamp()`.
    await updateDoc(documentRef, {
        'aut.firstName': 'NewFirstName',
        lut: serverTimestamp()
    });

    // The TypeScript compiler will fail to compile if the `data` argument to
    // `updateDoc()` is _not_ compatible with `WithFieldValue<PostDbModel>`.
    // This type checking prevents the caller from specifying objects with
    // incorrect properties or property values.
    // @ts-expect-error "Argument of type { title: string; } is not assignable
    // to parameter of type WithFieldValue<PostDbModel>"
    await updateDoc(documentRef, { title: 'New Title' });
    const snapshot2: DocumentSnapshot<Post> = await getDoc(documentRef);
    const post2: Post = snapshot2.data()!;
    if (post2) {
        assertEqual(post2.title, 'My Life');
        assertEqual(post2.author, 'NewFirstName Bar');
    }
}