foo.js

// controller
exports.likePost = function (req, res) {
    // validate the input
    req.checkBody('post_id', 'Post id is required').notEmpty();
    req.checkBody('post_id', 'Post id is needs to be an integer').isInt();
    req.checkBody('post_username', 'Post username is required').notEmpty();
    req.checkBody('like_username', 'Like username is required').notEmpty();

    var errors = req.validationErrors();

    console.log(errors);

    if (errors) {
        res.status(400).send(errors);
        return;
    }
    
    return postModel.likePost(req.body)
    .then(function () {
        res.sendStatus(200);
    })
    .catch(function (err) {
        console.log('MySQL Connection error: ' + err);
        res.sendStatus(500);
    });
}

// model
exports.likePost = function (post_data) {
    return knex.transaction(function (trx) {
        return trx.insert(post_data)
            .into('wall_post_likes')
        .then(function () {
            return trx('wall_post_likes')
                .increment('total_likes')
                .where('post_id', post_data.post_id);
        })
    });
};