recursive in callback functions

Question

I have a function with callback, where I'm using "listTables" method of dynamoDB, which returns just 100 table names and if there is anymore tables, it returns another field called "LastEvaluatedTableName" which we can use in our new query in listTables to query another 100 tables from the mentioned "LastEvaluatedTableName"; how can I have recursion in callbacks in javascript in this logic?

I have tried the following which is not correct:

module.exports.ListTables = function (start, callback) {
    var params;
    if (start) {
        params = {
            "ExclusiveStartTableName": start
        };
    }

    dynamodb.listTables(params, function (err, data) {
        var totalData = [];
        totalData.push(data);
        if (data.LastEvaluatedTableName) {
            data = module.exports.ListTables(data.LastEvaluatedTableName);
        }
        callback(err, totalData);

    });
}

Please let me know if you need more clarifications!

Thanks!

Shomz · Accepted Answer · 2014-12-01 01:50:35Z

1

You need to concat your data, not replace it each time:

dynamodb.listTables(params, function (err, data) {
    if (data.LastEvaluatedTableName) {
        data.concat(module.exports.ListTables(data.LastEvaluatedTableName));
    }
    callback(err, data);
});

UPDATE

Based on the info from the comment, sounds like you need something like this:

module.exports.ListTables = function (start, callback, totalData) {
    var params;
    if (start) {
        params = {
            "ExclusiveStartTableName": start
        };
    }

    if (!totalData) {
        totalData = [];
    }

    dynamodb.listTables(params, function (err, data) {
        totalData = totalData.concat(data.TableNames);
        if (data.LastEvaluatedTableName) {
            module.exports.ListTables(data.LastEvaluatedTableName, callback, totalData);
        }
        else {
            callback(err, totalData);
        }
    });
}

edited Dec 1, 2014 at 1:50

answered Dec 1, 2014 at 0:31

Shomz

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8 Comments

user385729 Over a year ago

Thansk so much man :-) Actuatly the result of ListTables from Dynamo is like : { LastEvaluatedTableName: 'test100', TableNames: [ 'test1',...]} and it seems it is not appending the results!

Shomz Over a year ago

You're welcome! Oh, I see, you know how to append the right stuff?

user385729 Over a year ago

it is an object so it gives ""Object #<Object> has no method 'concat'" so I tried data.TableNames.concat(module.exports.ListTables(data.LastEvaluatedTableName).TableNames); and this gives "Cannot read property 'TableNames' of undefined"

user385729 Over a year ago

The logic seems right, but still "Cannot read property 'TableNames' of undefined"...

Shomz Over a year ago

Damn, 3AM... forgot to assign the concatted data: totalData = totalData.concat(data.TableNames);. The case with no recursion should also work fine with that code.

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