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## Resource: wix-data

## Namespace: hooks

## Article: Introduction

## Article Link: https://dev.wix.com/docs/velo/apis/wix-data/hooks/introduction.md

## Article Content:

# Introduction
Data hooks run code before or after certain interactions with your site's
 collections. A data hook allows you to intercept the interaction immediately
 before or immediately after it occurs. The hook's code can even be used to
 affect the interaction itself. For example, you may want to intercept an
 item before it is added to your collection to perform a final validation or
 tweak the data that actually makes it into the collection.

 In general, hooks are run whether the interaction with your collection is
 initiated by a page element, programmatically, or when using the Content Management System (CMS).
 However, a Data API call from the backend code of your site may pass the
 optional `WixDataOptions` object and use it
 to suppress hooks from being called on that particular operation.

 > **Note**: This feature is not yet supported in [Wix Blocks](https://dev.wix.com/docs/build-apps/develop-your-app/frameworks/wix-blocks/about-wix-blocks.md).

 Code for the hooks is written in the **data.js** file, which resides in the **Backend** section of your site.
 Hook functions are defined using the following pattern:

 ``` javascript
 export function <collectionName>_<hookName>(<parameters>) { }
 ```
 You can add these functions to the **data.js** file by writing them yourself, or by generating templates using the Velo sidebar.

 To add a hook to a collection from the sidebar:
 1. Click the **Databases** button and hover over the relevant collection.
 1. Click the **Show More** icon.
 1. Select **Add/Remove Hooks**, and choose the hooks you want to add.
    ![Adding a Hook](https://wixmp-833713b177cebf373f611808.wixmp.com/images/velo-images/media_add_remove_hooks.png "Add/Remove Hook")