> For the complete documentation index, see [llms.txt](https://docs.appfarm.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.appfarm.io/appcademy/appfarm-fundamentals/app-data-fundamentals/data-source-filtering.md).

# Data Source Filtering

Data Source Filters are used to limit what Data is read into your App. 

Data Source Filters are important when the amount of data is large, since a large amount of data read could impact the loading speed of your App. In many cases, you also would want to limit the data due to sensitivity - e.g. for a customer portal, only read the data belonging to the logged in customer.

{% hint style="info" %}
A good principle with regards to Data Source Filtering: **Only read the data you need in your App.**
{% endhint %}

This topic gives you an overview of some ways of setting up filters on Data Sources.

### Video

You may see a video on Data Source Filtering below.

{% embed url="<https://www.loom.com/share/38bde959c9b6472dbf017830f2ccf80b>" %}
A video on Data Source Filtering
{% endembed %}

### Documentation

Relevant articles in our documentation:

* [Adding Data Sources, Data Source Settings and Filters](/reference/apps/data/data-sources.md#filter)
* [Filters](/reference/platform-concepts/filters.md)
* [Calendar Data Sources](/reference/apps/data/calendar-data-sources.md)


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