ReQL command: next

Command syntax

cursor.next(callback)
array.next(callback)
cursor.next() → promise
array.next() → promise

Description

Get the next element in the cursor.

Calling next the first time on a cursor provides the first element of the cursor. If the data set is exhausted (e.g., you have retrieved all the documents in a table), a ReqlDriverError error will be passed to the callback when next is called.

Example: Retrieve the next element.

cursor.next(function(err, row) {
    if (err) throw err;
    processRow(row);
});

Note: The canonical way to retrieve all the results is to use each or toArray. The next command should be used only when you may not retrieve all the elements of a cursor or want to delay some operations.

Example: You can retrieve all the elements of a cursor with the next command using recursion.

query.run( conn, function(err, cursor) {
    if (err) throw err;

    var fetchNext = function(err, result) {
        if (err) {
            if (((err.name === "ReqlDriverError") && err.message === "No more rows in the cursor.")) {
                console.log("No more data to process")
                // If you use one connection per query, the connection should be closed here.
                // conn.close()
            }
            else {
                throw err;
            }
        }
        else {
            processRow(result);
            cursor.next(fetchNext);
        }
    }
    cursor.next(fetchNext);
})

Example: With next, not all results have to be retrieved from a cursor – to stop retrieving results, break out of the recursive function. For example, this recursive function will stop retrieving results when the checkRow function returns true:

query.run( conn, function(err, cursor) {
    if (err) throw err;

    var fetchNext = function(err, result) {
        if (err) {
            if (((err.name === "ReqlDriverError") && err.message === "No more rows in the cursor.")) {
                console.log("No more data to process")
                // If you use one connection per query, the connection should be closed here.
                // conn.close()
            }
            else {
                throw err;
            }
        }
        else {
            if (checkRow(result)) {
                cursor.next(fetchNext);
            }
            else {
                cursor.close()
                // If you use one connection per query, the connection should be closed here.
                // conn.close()
            }
        }
    }
    cursor.next(fetchNext);
})

Example: You can retrieve all the elements of a cursor with the next command using recursion and promises.

query.run(conn).then(function(cursor) {
    var errorHandler = function(err) {
        if (((err.name === "ReqlDriverError") && err.message === "No more rows in the cursor.")) {
            console.log("No more data to process")
            // If you use one connection per query, the connection should be closed here.
            // conn.close()
        }
        else {
            throw err;
        }
    }
    var fetchNext = function(result) {
        processRow(result);
        cursor.next().then(fetchNext).error(errorHandler);
    }

    cursor.next().then(fetchNext).error(errorHandler);
}).error(function(err) {
    throw err;
});

Related commands

• each
• toArray
• close (cursor)

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