# Preloading custom data and fields in the topic list
**URL:** https://meta.discourse.org/t/preloading-custom-data-and-fields-in-the-topic-list/57389
**Category:** Development
**Created:** [February 14, 2017, 9:45pm UTC](https://meta.discourse.org/t/preloading-custom-data-and-fields-in-the-topic-list/57389 "2017-02-14T21:45:09Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@sam](https://meta.discourse.org/u/sam)
#### Post date: [February 14, 2017, 9:45pm UTC](https://meta.discourse.org/t/preloading-custom-data-and-fields-in-the-topic-list/57389/1 "2017-02-14T21:45:10Z")
Certain plugins need the ability to “preload” data in the topic list.
Some specific examples:
- Discourse solved adds an icon on the topic list when a topic is solved
- Discourse assign will display the username the topic is assigned to on the topic list
To achieve that we have 2 mechanisms:
### Preloading a custom field
If you have any custom fields you need for rendering of the topic list use:
```plaintext
TopicList.preloaded_custom_fields << "my_custom_field"
```
This will force the system to ensure that the Topic object model has the custom field loaded when serializing.
If you do not do that and try to access a custom field an error will be raised.
###Preloading custom data
In some cases you may need to preload custom data that goes beyond a custom field. To do so:
```ruby
TopicList.on_preload do |topics, topic_list|
# your custom code to load up all topic data in bulk goes here
end
```
This is useful when you need to reach out and preload other models.
By carefully using both these methods you can ensure your plugin does not cause N+1 queries.
---
### Author:  [@codinghorror](https://meta.discourse.org/u/codinghorror)
#### Post date: [February 14, 2017, 10:00pm UTC](https://meta.discourse.org/t/preloading-custom-data-and-fields-in-the-topic-list/57389/2 "2017-02-14T22:00:26Z")
I believe Feature Voting plugin currently has n+1 queries and perhaps for the same reasons?
---
### Author:  [@sam](https://meta.discourse.org/u/sam)
#### Post date: [February 14, 2017, 10:01pm UTC](https://meta.discourse.org/t/preloading-custom-data-and-fields-in-the-topic-list/57389/3 "2017-02-14T22:01:30Z")
very possible, I only added the ability to preload custom data today.
---
### Author:  [@Falco](https://meta.discourse.org/u/Falco)
#### Post date: [February 14, 2017, 10:03pm UTC](https://meta.discourse.org/t/preloading-custom-data-and-fields-in-the-topic-list/57389/4 "2017-02-14T22:03:58Z")
This will make a lot of plugins use way less code, like my signatures plugin.
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### Author:  [@sam](https://meta.discourse.org/u/sam)
#### Post date: [February 14, 2017, 10:04pm UTC](https://meta.discourse.org/t/preloading-custom-data-and-fields-in-the-topic-list/57389/5 "2017-02-14T22:04:35Z")
Does signature show up in topic list? scary …
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### Author:  [@Falco](https://meta.discourse.org/u/Falco)
#### Post date: [February 14, 2017, 10:06pm UTC](https://meta.discourse.org/t/preloading-custom-data-and-fields-in-the-topic-list/57389/6 "2017-02-14T22:06:34Z")
> [@sam](#):
>
> Does signature show up in topic list? scary …
Oh no, misread as post list. 😄
Will there be an analogous feature to the post stream?
---
### Author:  [@sam](https://meta.discourse.org/u/sam)
#### Post date: [February 14, 2017, 10:07pm UTC](https://meta.discourse.org/t/preloading-custom-data-and-fields-in-the-topic-list/57389/7 "2017-02-14T22:07:03Z")
I would be happy to add an analogous feature, makes sense there as well.
---
### Author:  [@joebuhlig](https://meta.discourse.org/u/joebuhlig)
#### Post date: [February 15, 2017, 2:04am UTC](https://meta.discourse.org/t/preloading-custom-data-and-fields-in-the-topic-list/57389/8 "2017-02-15T02:04:19Z")
> [@codinghorror](#):
>
> I believe Feature Voting plugin currently has n+1 queries
It used to. I think I’ve cleaned most of those up. I don’t know of any others.
[https://github.com/discourse/discourse-feature-voting/commit/135eaf8a5ec0e37b64adf10971384ee88abec580](https://github.com/discourse/discourse-feature-voting/commit/135eaf8a5ec0e37b64adf10971384ee88abec580)
> [@codinghorror](#):
>
> and perhaps for the same reasons?
I had to preload the custom fields due to errors if the data was blank. It was tricky to debug at first because I had existing data so I couldn’t replicate the errors reported. Then someone mentioned this process in Babble. Once I implemented it, the errors were gone. I never looked into it further than that.
---
### Author:  [@angus](https://meta.discourse.org/u/angus)
#### Post date: [January 17, 2025, 3:36pm UTC](https://meta.discourse.org/t/preloading-custom-data-and-fields-in-the-topic-list/57389/9 "2025-01-17T15:36:46Z")
Just for anyone reading this in 2025 I’ve written an updated version on the same topic
> [@Preloading data and dealing with N+1 Query problems](https://meta.discourse.org/t/preloading-data-and-dealing-with-n-1-query-problems/347688):
>
> When working with the Discourse rails application, whether building a plugin, or making a pull request to discourse/discourse there are a number of contexts where you’ll encounter N+1 query problems. This topic explains how to handle data preloading to address such problems and keep Discourse performant. N+1 Query Problems in Rails First, if you’re not already familiar with N+1 query problems, and how Rails addresses them, check out this section of the guides. Topics The N+1 issues to look ou…