Comments won't save to mongoDB database (using nodejs, express, mongoose)

//create express function
const express = require('express');
const morgan = require('morgan');
const mongoose = require('mongoose');
const blogRoutes = require('./routes/blogRoutes');
const commentRoutes = require('./routes/commentRoutes');

//set up express app and invoke express and stor in app const
const app = express();
app.listen(3000)
// //connect to mongodb
const bdURI = 'mongodb+srv://something:somepass@nodetuts-6iczn.mongodb.net/node-tuts?retryWrites=true&w=majority';

// //deprecation warning so add 2nd parameter
mongoose.connect(bdURI, { useNewUrlParser: true, useUnifiedTopology: true })
    .then(result => app.listen(8080))
    .catch(err => console.log(err));

//set up view engine
app.set('view engine', 'ejs');

//middleware on static files
app.use(express.static('public'));
app.use(express.urlencoded({ extended: true }));
app.use(morgan('dev'));

//routes
app.get('/', (req, res) => {
    res.redirect('/blogs');
});

app.get('/about', (req, res) => {
    res.render('about', { title: 'about' });
});

//blog routes
//scope out the /blog and then remove /blog in all routes. It makes it easier if you want to change url later on
app.use('/blogs', blogRoutes);
app.use('/blogs', commentRoutes);

//404 must be last
app.use((req, res) => {
    res.status(404).render('404' , { title: '404' });
});

const mongoose = require('mongoose');

const Schema = mongoose.Schema;

const commentSchema = new Schema({
    blog_id: {
        type: String
    },
    blog_name: {
        type: String
    },
    comment: {
        type: String
    }
}, { timestamps: true });

const Comment = mongoose.model('Comment', commentSchema);
module.exports = Comment;

const Comment = require('../models/comment');

const comment_create_get = (req, res) => {
    res.render('comments/comments', { title: 'create new blog' });
}

const post_comment = (req, res) => {
    const comment = new Comment({
        blog_id: 'df12345',
        blog_name: 'This a a blog with comment',
        comment: 'this is a comment 3'
    });
    comment.save()
        .then(result => res.redirect('/blogs'))
        .catch(err => console.log(err));
};

module.exports = {
    post_comment,
    comment_create_get
}

const express = require('express');
const commentController = require('../controllers/commentController');

const router = express.Router();

router.get('/', commentController.comment_create_get);

router.post('/', commentController.post_comment);

module.exports = router;