How to run knex queries and insert in band - postgresql

Question

I have a sql table like this:
// Create table for albums - photos relation with ordering
await knex.schema.createTable('albums_photos', (table) => {
table.integer('album')
.notNullable()
.references('pk')
.inTable('albums')
.onUpdate('CASCADE')
.onDelete('CASCADE')
table.integer('photo')
.notNullable()
.references('pk')
.inTable('photos')
.onUpdate('CASCADE')
.onDelete('CASCADE')
// Photo's order in its album
table.integer('order').notNullable()
})
I did not add db constraint yet but album and order must be unique together.
When I add a new entrie, I want order to be equal to the max value of order for given album, + 1:
async createAlbumPhoto = (albumPk, photoPk) => {
console.log(`Work on photo ${photoPk}`)
// We get current max value for order and album
const maxData = await knex('albums_photos')
.where({ album: albumPk })
.max('order')
.first()
console.log(`Get max ${maxData.max} for photo ${photoPk}`)
// We create new entrie with max + 1
const newAlbumPhoto = await knex('albums_photos')
.insert({
album: albumPk,
photo: photoPk,
order: maxData.max + 1
})
.returning('*')
console.log(`pk ${photoPk} done with order ${newAlbumPhoto[0].order}`)
return newAlbumPhoto[0]
}
When I insert only one photo_album in a while, everything works fine.
But when (web) client send multiple requests one after another, due to asynchronous db requests, I get bad results. Such list of photo pks ['71', '72', '73', '74'] results in:
work on pk 71 (OK)
Get max null for photo 71 (OK)
pk 71 done with order 1 (OK)
work on pk 72
work on pk 73
Get max 1 for photo 72 (OK)
Get max 1 for photo 73 (Wrong)
work on pk 74
Get max 1 for photo 74 (Wrong)
pk 72 done with order 2 (OK)
pk 73 done with order 2 (Wrong)
pk 74 done with order 2 (Wrong)
Orders aren't unique…