# What does the migration file do?
**URL:** https://discourse.cataclysmdda.org/t/what-does-the-migration-file-do/14276
**Category:** The Garage
**Created:** [September 24, 2017, 1:03am UTC](https://discourse.cataclysmdda.org/t/what-does-the-migration-file-do/14276 "2017-09-24T01:03:16Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@DeWolf](https://discourse.cataclysmdda.org/u/DeWolf)
#### Post date: [September 24, 2017, 1:03am UTC](https://discourse.cataclysmdda.org/t/what-does-the-migration-file-do/14276/1 "2017-09-24T01:03:16Z")
Exactly as the title says or rather what do these migration do if anything?
---
### Author:  [@Zhilkin](https://discourse.cataclysmdda.org/u/Zhilkin)
#### Post date: [September 24, 2017, 7:22pm UTC](https://discourse.cataclysmdda.org/t/what-does-the-migration-file-do/14276/2 "2017-09-24T19:22:28Z")
> [@DeWolf](#):
>
> Exactly as the title says or rather what do these migration do if anything?
When savegame is loaded certain entities (which are not in the game) from migration.json are transformed to other entities (which are still in the game).
---
### Author:  [@DeWolf](https://discourse.cataclysmdda.org/u/DeWolf)
#### Post date: [September 24, 2017, 7:40pm UTC](https://discourse.cataclysmdda.org/t/what-does-the-migration-file-do/14276/3 "2017-09-24T19:40:20Z")
> [@Zhilkin](#):
>
> [quote=“DeWolf, post:1, topic:14276”]Exactly as the title says or rather what do these migration do if anything?
When savegame is loaded certain entities (which are not in the game) from migration.json are transformed to other entities (which are still in the game).[/quote]
Oh. Neat. So I guess another question would be why can’t I change the mod location of the combat/fighting knives or rather why are those specific ids when used as weapon mods stock to the underbarrel slot?