exports.update = function(req, res) {

    // Validate input, in our case we will recive a json if 
    // all changeable informations, in activity's
    // perspective we to recive the ID of activity and the
    // description, so, we check if its not blank
    if(!req.params.activityId) {
        return res.status(400).send({
            message: "Acitivity's ID cannot be empty"
        });
    }
    if(!req.body.description) {
        return res.status(400).send({
            message: "Activity's description cannot be empty"
        });
    }

    // Normally on our project we are using await/async
    // but in that case is pretty simple to use the standart promise
    // so, without await/async but with just then at the and of a function
    AcitivityModel.update(
        { description: req.body.description },
        { where: { id: req.params.activityId } }
    ).then(function(updateStatus) {
        // First of all, what happens above:
        // update is a function that recives two parameters and returns a update status
        // the first of those two parameters is: a map of column: newValue that should be updated
        // the second one is: a map with your where clause
        // its update status return is a array if just one position, where 0 extends for failure
        // and 1 for success

        // Now, about the promises, when we finish a function we can add a .then at its end
        // making the "then" function just happen after our main function, we also can take
        // whatever the main function send back to the caller, so, we have a new function
        // reciving the 'updateStatus' that was the result from the update

        if(updateStatus[0] === 0) {
            // 0 means failure, so throw a error
            return res.status(404).send({
                message: "Acitivity not found with ID " + req.params.activityId + "."
            });
        } else if(updateStatus[0] === 1) {
            // 1 means success, so throw a success message
            return res.status(200).send({
                message: "Acitivity with ID equals to " + req.params.activityId + " updated successfully."
            });
        } else {
            // Just to be sure that non special situation might pass
            return res.status(500).send({
                message: "Error updating activity with ID " + req.params.activityId + "."
            });
        }
    }).catch(function(err) {
        // Checking anykind of exceptions
        if(err.kind === 'ObjectId') {
            return res.status(404).send({
                message: "Acitivity not found with ID " + req.params.activityId + "."
            });
        }
        return res.status(500).send({
            message: "Error updating activity with ID " + req.params.activityId + "."
        });
    });
};