Question

我正在尝试使用Promise.all（）同时执行许多Firebase Cloud Storage查询：

exports.onNewOrder = 
functions.database.ref('/orders/{orderId}').onCreate(event => {  
    const data = event.val();
    const orderedBy = data.ordered_by;
    const creations = data.creations;

    var promises = []
    for (var entry of creations.entries()) {
        var key = entry[0], value = entry[1];
        var creationPromise = admin.database().ref("creations/"+ key);
        creationPromise.once("value")
        .then((crSnapshot)=>{
            const crName = crSnapshot.val().name;
            const created = crSnapshot.val().created;
            return "crName+'\n'+created”;
        }).catch((error) => {
            console.log("creation details error : "+ error);
        });
        promises.push(creationPromise);
    }

    const userPromise = admin.database().ref("users/"+ orderedBy);
    userPromise.once("value")
    .then((snapshot) => {
        var name = snapshot.val().name;
        var email = snapshot.val().email;
        const userDetails = name+'\n'+email;
        return userDetails; 
    }).catch((error) => {
        console.log("user details error :"+ error);
    });

    promises.push(userPromise);

    return Promise.all(promises).then(results => {
        console.log("results: " + results)
        return true;
    }).catch((error) => {
        console.log("sendMail failed : "+ error);
    });
});

我希望看到每个已执行的Promise的完整查询结果，但是我得到的却是以下内容：

结果：

https://....firebaseio.com/creations/cr_1bfd5f16212f44c792a2cbe3e9c6e4cc
https://....firebaseio.com/creations/cr_343c363c2a214487ba8cb7101653f6af
https://....firebaseio.com/creations/cr_e3f7a0bafd1542ac898d96e86155b94e
https://....firebaseio.com/users/us_5e4c28e18e63454c861caa5c4fe6a6f0

我想念什么吗？

Answer 1

以下应该可以解决问题。

详细的here：

Promise.all(iterable)方法返回一个Promise 当iterable参数中的所有诺言都具有时解析已解决或iterable参数不包含诺言的情况。它拒绝的原因是第一个拒绝的承诺。

因此，您需要向promises数组添加一些承诺。

once()方法确实返回了承诺，如文档中的here所述。

exports.onNewOrder = 
functions.database.ref('/orders/{orderId}').onCreate(event => {  
    const data = event.val();
    const orderedBy = data.ordered_by;
    const creations = data.creations;

    const promises = []

    for (var entry of creations.entries()) {
        var key = entry[0];
        var creationPromise = admin.database().ref("creations/"+ key).once("value");
        promises.push(creationPromise);
    }

    const userPromise = admin.database().ref("users/"+ orderedBy).once("value");
    promises.push(userPromise);

    return Promise.all(promises)
    .then(results => {
        console.log("results: " + results);
        return true;
        //actually here you will probably do something else than just write the results to the console. 
        //In this case you should return a promise (instead of true).
    }).catch((error) => {
        console.log("sendMail failed : "+ error);
        return false;
    });

});

使用Promise运行并发Firebase请求

1 个答案: