递归，Node js和异步调用

debugcn 发表于 Dev

塔希尔·米尔扎（Tahir Mirza）|

我试图将savePlaces数组作为最终输出，以便可以在响应中返回它。但是我在function2（）中获得了未定义的成功。为什么我没有按预期获得savePlaces。请提供解决方案。

var saveOverriddenPlaces = function(index, savePlaces) {
    var groupSettingsDAO = new GroupSettingsDAO();
    var deferred = q.defer();
    if (index == savePlaces.length) {
        console.log("-----------------------------deferred--------------------------------", deferred);
        console.log("LAST RETURN -----------------------------" + savePlaces + "----------------------------------------------------", index);
        deferred.resolve(savePlaces);
        return deferred.promise;
    }
    var placeInfo = {
        "id": savePlaces[index].id,
        "groupurl": savePlaces[index].groupurl,
        "sla": savePlaces[index].sla
    };
    if (savePlaces[index]._id) {
        placeInfo._id = savePlaces[index]._id;
        //update the overriden places in the database
        groupSettingsDAO.updateOverriddenPlace(placeInfo)
            //updates the overriden place and sends result in response when successful else logs error
            .then(
                //success
                function(success) {
                    console.log("recursion ============" + index + "=======================");
                    deferred.resolve(saveOverriddenPlaces(++index, savePlaces));

                    return deferred.promise;
                },
                //failure
                function(error) {
                    console.log("PLACES     ERROR ===================================", error);
                });
        // placesWithID.push(value);
    }
    //WITHOUT ids
    else {
        placeInfo._id = guid();
        savePlaces[index]._id = placeInfo._id;
        groupSettingsDAO.saveOverriddenPlace(placeInfo)
            // saves the overridden place and sends the results in response if successful else logs the error
            .then(
                //success
                function(success) {
                    console.log("recursion ============" + index + "=======================");
                    deferred.resolve(saveOverriddenPlaces(++index, savePlaces));
                },
                //failure
                function(error) {
                    console.log("PLACES     ERROR ===================================", error);

                });
    }
}
function2(req, res) {
    saveOverriddenPlaces(0, req.savePlaces).then(function(success) {
        //getting success as undefined 
        res.send({
            "result": success
        });
    });
}

贝吉

问题在于

deferred.resolve(saveOverriddenPlaces(++index, savePlaces));

您的saveOverriddenPlaces函数不会（总是）返回承诺或值。如果一个函数是异步的，则它必须始终返回一个Promise。

您可以通过在条件语句中return的groupSettingsDAO.…().then(…)调用之前添加a来轻松实现此目的-如果您从其回调中获得了一个价值/承诺，它也会准确地then返回您想要的承诺return。

但是，您应尽量避免延迟使用反模式。对于您的基本情况，使用该Q函数创建已兑现的承诺，其他所有操作只需链式then调用-无需延迟。

function saveOverriddenPlaces(index, savePlaces) {
    if (index == savePlaces.length) {
        console.log("LAST RETURN -" + savePlaces + "-", index);
        return Q(savePlaces);
    }
    var groupSettingsDAO = new GroupSettingsDAO();
    var placeInfo = {
        "id": savePlaces[index].id,
        "groupurl": savePlaces[index].groupurl,
        "sla": savePlaces[index].sla
    };
    var promise;
    if (savePlaces[index]._id) {
        placeInfo._id = savePlaces[index]._id;
        promise = groupSettingsDAO.updateOverriddenPlace(placeInfo); //update the overriden places in the database
        // placesWithID.push(value);
    } else { // WITHOUT ids
        placeInfo._id = guid();
        savePlaces[index]._id = placeInfo._id;
        promise = groupSettingsDAO.saveOverriddenPlace(placeInfo) // saves the overridden place
    }
    return promise.then(function(success) {
//  ^^^^^^
        console.log("recursion =" + index + "=" + success);
        return saveOverriddenPlaces(++index, savePlaces));
//      ^^^^^^
    });
}
function2(req, res) {
    saveOverriddenPlaces(0, req.savePlaces).then(function(success) {
        //getting success as undefined 
        res.send({
            "result": success
        });
    }, function(error) {
        console.log("PLACES ERROR =", error);
    });
}