How to select DB Expression as value using knex/Bookshelf - mysql

Question

I'm trying to execute the following query using knex.js and MySql
SELECT
m.id,
TIME(date_created) AS `timestamp`,
u.username,
m.`message`
FROM
`messages` AS m
INNER JOIN users AS u ON u.id = m.user_id
WHERE
m.game_id IS NULL
AND m.`date_created` > DATE_SUB(
CURRENT_TIMESTAMP (),
INTERVAL 12 HOUR
)
ORDER BY
m.`date_created` ASC
LIMIT 50
For proper handling expressions in where closure such as DATE_SUB(CURRENT_TIMESTAMP(), INTERVAL 12 HOUR) according to documentation there is whereRow() method in knex.
I tried to use select() method as
select('messages.id', 'TIME(date_created) AS timestamp', 'users.username', 'messages.message')
But knex masks TIME(date_created) expression in a way it should to be a column name. Does anybody know a way to use a custom expressions in selects?

Answer 1

I did not found exact answer on my question but I've found a solution which allows me to move forward. I created separate model which uses standard Bookshelf(knex) export:
var Bookshelf = require('bookshelf')(knex);
module.exports.DB = Bookshelf;
And created separate method in that model where I could use DB.knex.raw() for masking DB expressions in SELECT. So I became able to write the query above in the following way:
var DB = require('./../db').DB;
var Messages = DB.Model.extend({
tableName: 'messages',
hasTimestamps: false,
idAttribute: 'id'
},
{
getMessagesHistory: function (gameId) {
return this.query().select('messages.id', DB.knex.raw('TIME(date_created) AS timestamp'), 'users.username', 'messages.message')
.innerJoin('users', 'messages.user_id', 'users.id')
.whereRaw("messages.game_id " + (gameId == 0 ? "IS NULL" : "= " + gameId))
.andWhereRaw("messages.date_created > DATE_SUB(CURRENT_TIMESTAMP(), INTERVAL 12 HOUR)")
.orderBy('messages.date_created', 'ASC')
.limit(50);
}
}
);
module.exports = Messages;

Answer 2

You can wrap any argument with knex.raw() to tell the framework that it's a raw piece of SQL:
select(
'messages.id',
knex.raw('TIME(date_created) AS timestamp'),
'users.username',
'messages.message',
)
See http://knexjs.org/#Raw-Bindings