# Using HasCustomFields in a plugin
**URL:** https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469
**Category:** Development
**Created:** [January 18, 2021, 5:50pm UTC](https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469 "2021-01-18T17:50:53Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@pfaffman](https://meta.discourse.org/u/pfaffman)
#### Post date: [January 18, 2021, 5:50pm UTC](https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469/1 "2021-01-18T17:50:53Z")
I have a model in a plugin. The model is `Pfaffmananger::Server`, the table is `pfaffmanager_servers`. For Reasons, I want to have custom fields for this model (I expect there to be ways that I want to extend the server data that are likely to be used only for a few instances and I don’t want a zillion mostly-unused fields in the model).
Here’s the migration that creates the table:
```ruby
class CreatePfaffmanagerServerCustomField < ActiveRecord::Migration[6.0]
def change
create_table :pfaffmanager_server_custom_fields do |t|
t.integer :server_id, null: false
t.string :name, limit: 256, null: false
t.text :value
t.timestamps null: false
end
add_index :pfaffmanager_server_custom_fields, [:server_id, :name]
end
end
```
If I use `pfaffmanager_server_id` instead of `server_id` the migration fails because it can’t find `server_id`, but when I use `pfaffmanager_server_id` for the field name, when I go to save a server after I create a custom field, I get:
```ruby
Pfaffmanager::ServerCustomField Load (0.4ms) SELECT "pfaffmanager_server_custom_fields".* FROM "pfaffmanager_server_custom_fields" WHERE "pfaffmanager_server_custom_fields"."server_id" = 1
(0.2ms) ROLLBACK
PG::UndefinedColumn: ERROR: column "pfaffmanager_server_id" of relation "pfaffmanager_server_custom_fields" does not exist
LINE 1: INSERT INTO pfaffmanager_server_custom_fields (pfaffmanager_...
```
So if the migration has field `pfaffmanager_server_id` the migration fails, and if the field name is `server_id` the save fails.
I’m looking at `save_custom_fields` in `concers/has_custom_fields.rb`, but can’t quite figure out if there’s some way to override that.
Is there something that I can do besides refactor the whole thing to use server rather than pfaffmanager\_server?
---
### Author:  [@david](https://meta.discourse.org/u/david)
#### Post date: [January 18, 2021, 5:55pm UTC](https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469/2 "2021-01-18T17:55:26Z")
> [@pfaffman](#):
>
> If I use `pfaffmanager_server_id` instead of `server_id` the migration fails because it can’t find `server_id`
Did you also update the `add_index` call to point to `pfaffmanager_server_id`?
---
### Author:  [@pfaffman](https://meta.discourse.org/u/pfaffman)
#### Post date: [January 18, 2021, 8:19pm UTC](https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469/3 "2021-01-18T20:19:55Z")
Thanks so much, David!
> [@david](#):
>
> Did you also update the `add_index` call to point to `pfaffmanager_server_id` ?
Yes. That could be my problem. I guess that’s the error message I should have included. And I can make the migration work with either field (though with `pfaffmanager_server_id` as the field name, the index name becomes \> 63 characters, so I have to use a different name for the index.
Let me try again.
### `server_id` as the field name
```ruby
class CreatePfaffmanagerServerCustomField < ActiveRecord::Migration[6.0]
def change
create_table :pfaffmanager_server_custom_fields do |t|
t.integer :server_id, null: false
t.string :name, limit: 256, null: false
t.text :value
t.timestamps null: false
end
add_index :pfaffmanager_server_custom_fields, [:server_id, :name]
end
end
```
Fails on save with:
```plaintext
Pfaffmanager::ServerCustomField Load (3.8ms) SELECT "pfaffmanager_server_custom_fields".* FROM "pfaffmanager_server_custom_fields" WHERE "pfaffmanager_server_custom_fields"."server_id" = 1
(1.4ms) ROLLBACK
PG::UndefinedColumn: ERROR: column "pfaffmanager_server_id" of relation "pfaffmanager_server_custom_fields" does not exist
LINE 1: INSERT INTO pfaffmanager_server_custom_fields (pfaffmanager_...
^
```
So it’s looking for `pfaffmanager_server_id`. Now, let’s use `pfaffmanager_server_id`.
### `pfaffmanager_server_id` as field name
Here’s the migration:
```ruby
class CreatePfaffmanagerServerCustomField < ActiveRecord::Migration[6.0]
def change
create_table :pfaffmanager_server_custom_fields do |t|
t.integer :pfaffmanager_server_id, null: false
t.string :name, limit: 256, null: false
t.text :value
t.timestamps null: false
end
add_index :pfaffmanager_server_custom_fields,
[:pfaffmanager_server_id, :name],
name: 'index_pfaffmanager_server_custom_fields_on_server_id_and_name'
end
end
```
Here’s what happens when I try `s.custom_fields` (the above was able to return `nil` for this but didn’t fail until I tried to **save** a custom field). I `register_custom_field_type` [here](https://github.com/pfaffman/discourse-pfaffmanager/blob/master/app/models/pfaffmanager/server.rb#L23-L28)):
```plaintext
pry(main)> s.custom_fields
(1.1ms) SELECT "pfaffmanager_server_custom_fields"."name", "pfaffmanager_server_custom_fields"."value" FROM "pfaffmanager_server_custom_fields" WHERE "pfaffmanager_server_custom_fields"."server_id" = 1 ORDER BY id asc
ActiveRecord::StatementInvalid: PG::UndefinedColumn: ERROR: column pfaffmanager_server_custom_fields.server_id does not exist
LINE 1: ...e" FROM "pfaffmanager_server_custom_fields" WHERE "pfaffmana...
^
from /home/pfaffman/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/rack-mini-profiler-2.3.0/lib/patches/db/pg.rb:69:in `exec_params'
Caused by PG::UndefinedColumn: ERROR: column pfaffmanager_server_custom_fields.server_id does not exist
LINE 1: ...e" FROM "pfaffmanager_server_custom_fields" WHERE "pfaffmana...
^
```
Now it’s looking for `server_id`.
So it seems like `custom_fields` wants it one way a `save_custom_fields` wants it the other.
It doesn’t care what the index name is, does it?
---
### Author:  [@david](https://meta.discourse.org/u/david)
#### Post date: [January 18, 2021, 8:36pm UTC](https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469/4 "2021-01-18T20:36:16Z")
> [@pfaffman](#):
>
> It doesn’t care what the index name is, does it?
I don’t think so, no
I think the second approach is probably the one to aim for (using `pfaffman_server_id` as the column name)
I wonder if overriding this method may help:
>
You can check the current value on the console like
```ruby
Server.new.custom_fields_fk
```
If that’s `server_id`, then I suggest overriding that method in your `Server` model
```ruby
class Server < ...
def custom_fields_fk
"pfaffman_server_id"
end
end
```
---
### Author:  [@david](https://meta.discourse.org/u/david)
#### Post date: [January 18, 2021, 8:46pm UTC](https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469/5 "2021-01-18T20:46:47Z")
Or maybe it’s this bit 🤔
>
---
### Author:  [@pfaffman](https://meta.discourse.org/u/pfaffman)
#### Post date: [January 18, 2021, 8:54pm UTC](https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469/6 "2021-01-18T20:54:15Z")
Thanks so much! So
`Server.new.custom_fields_fk` is `pfaffmanager_server_id` if I use `pfaffmanager_serfver_id`. So maybe I should use `server_id` and then override as you suggested above.
It looks like `refresh_custom_fields_from_db` is trying to use the wrong names. I don’t quite understand what `_custom_fields.order...` is doing.
>
I’m going to see what happens if I use `server_id` and if I can then override `custom_fields_fk`
---
### Author:  [@pfaffman](https://meta.discourse.org/u/pfaffman)
#### Post date: [January 18, 2021, 9:13pm UTC](https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469/7 "2021-01-18T21:13:29Z")
Ha! You did it! Thanks so much. I switched it to `server_id` and then did this in my `server.rb` model:
```ruby
def custom_fields_fk
@custom_fields_fk ||= "server_id"
end
```
As long as that’s going to override that only for this model and not break `user_custom_field` and friends I think I should be ready to start beating myself over the head again on [Best way to enforce permissions--controller or constraint?](https://meta.discourse.org/t/best-way-to-enforce-permissions-controller-or-constraint/176113). And then I can add routes to do stuff like fill my new custom fields with . . . something.
I can’t thank you enough. You likely saved me a whole day. I owe you a 🍺!
---
### Author:  [@david](https://meta.discourse.org/u/david)
#### Post date: [January 18, 2021, 9:16pm UTC](https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469/8 "2021-01-18T21:16:15Z")
> [@pfaffman](#):
>
> I switched it to `server_id` and then did this in my `server.rb` model:
Great! 🎉 If you can think of a way to make it more generic then that would certainly be PR-welcome.
---
### Author:  [@pfaffman](https://meta.discourse.org/u/pfaffman)
#### Post date: [January 18, 2021, 9:17pm UTC](https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469/9 "2021-01-18T21:17:53Z")
If something occurs to me I’ll let you know or submit a PR, but I have to think that a plugin that wants to use custom fields is pretty far out on the edge.
---
### Author:  [@pfaffman](https://meta.discourse.org/u/pfaffman)
#### Post date: [April 27, 2024, 1:01am UTC](https://meta.discourse.org/t/using-hascustomfields-in-a-plugin/176469/10 "2024-04-27T01:01:14Z")
OM\_fk\_G.
`custom_fields_fk` seemed so stupid that I assumed it was something that I meant to delete and had named it something stupid so I’d know it was safe to delete it later. It was later, so I deleted it. And then my specs failed.
There was even a comment with a link to this topic in the code.