Field Hooks

Field-level hooks offer incredible potential for encapsulating your logic. They help to isolate concerns and package up functionalities to be easily reusable across your projects.

Example use cases include:

Automatically add an owner relationship to a Document based on the req.user.id
Encrypt / decrypt a sensitive field using beforeValidate and afterRead hooks
Auto-generate field data using a beforeValidate hook
Format incoming data such as kebab-casing a document slug with beforeValidate
Restrict updating a document to only once every X hours using the beforeChange hook

All field types provide the following hooks:

beforeValidate
beforeChange
afterChange
afterRead

Config

Example field configuration:

1import { Field } from 'payload/types';
2
3const ExampleField: Field = {
4  name: 'name',
5  type: 'text',
6  hooks: {
7    beforeValidate: [(args) => {...}],
8    beforeChange: [(args) => {...}],
9    afterChange: [(args) => {...}],
10    afterRead: [(args) => {...}],
11  }
12}

Arguments and return values

All field-level hooks are formatted to accept the same arguments, although some arguments may be undefined based on which field hook you are utilizing.

Arguments

Field Hooks receive one args argument that contains the following properties:

Option	Description
`data`	The data passed to update the document within `create` and `update` operations, and the full document itself in the `afterRead` hook.
`siblingData`	The sibling data passed to a field that the hook is running against.
`findMany`	Boolean to denote if this hook is running against finding one, or finding many within the `afterRead` hook.
`operation`	A string relating to which operation the field type is currently executing within. Useful within `beforeValidate`, `beforeChange`, and `afterChange` hooks to differentiate between `create` and `update` operations.
`originalDoc`	The full original document in `update` operations. In the `afterChange` hook, this is the resulting document of the operation.
`previousDoc`	The document before changes were applied, only in `afterChange` hooks.
`previousSiblingDoc`	The sibling data of the document before changes being applied, only in `beforeChange` and `afterChange` hook.
`req`	The Express `request` object. It is mocked for Local API operations.
`value`	The value of the field.
`previousValue`	The previous value of the field, before changes, only in `beforeChange` and `afterChange` hooks.
`context`	Context passed to this hook. More info can be found under Context
`field`	The field which the hook is running against.
`collection`	The collection which the field belongs to. If the field belongs to a global, this will be null.
`global`	The global which the field belongs to. If the field belongs to a collection, this will be null.

Return value

All field hooks can optionally modify the return value of the field before the operation continues. Field Hooks may optionally return the value that should be used within the field.

To better illustrate how field-level hooks can be applied, here are some specific examples. These demonstrate the flexibility and potential of field hooks in different contexts. Remember, these examples are just a starting point - the true potential of field-level hooks lies in their adaptability to a wide array of use cases.

beforeValidate

Runs before the update operation. This hook allows you to pre-process or format field data before it undergoes validation.

1import { Field } from 'payload/types'
2
3const usernameField: Field = {
4  name: 'username',
5  type: 'text',
6  hooks: {
7    beforeValidate: [({ value }) => {
8      // Trim whitespace and convert to lowercase
9      return value.trim().toLowerCase()
10    }],
11  }
12}

In this example, the beforeValidate hook is used to process the username field. The hook takes the incoming value of the field and transforms it by trimming whitespace and converting it to lowercase. This ensures that the username is stored in a consistent format in the database.

beforeChange

Immediately following validation, beforeChange hooks will run within create and update operations. At this stage, you can be confident that the field data that will be saved to the document is valid in accordance to your field validations.

1import { Field } from 'payload/types'
2
3const emailField: Field = {
name: 'email',
type: 'email',
hooks: {
  beforeChange: [({ value, operation }) => {
    if (operation === 'create') {
      // Perform additional validation or transformation for 'create' operation
    }
    return value
  }],
}
14}

In the emailField, the beforeChange hook checks the operation type. If the operation is create, it performs additional validation or transformation on the email field value. This allows for operation-specific logic to be applied to the field.

afterChange

The afterChange hook is executed after a field's value has been changed and saved in the database. This hook is useful for post-processing or triggering side effects based on the new value of the field.

1import { Field } from 'payload/types'
2
3const membershipStatusField: Field = {
name: 'membershipStatus',
type: 'select',
options: [
  { label: 'Standard', value: 'standard' },
  { label: 'Premium', value: 'premium' },
  { label: 'VIP', value: 'vip' }
],
hooks: {
  afterChange: [({ value, previousValue, req }) => {
    if (value !== previousValue) {
      // Log or perform an action when the membership status changes
      console.log(`User ID ${req.user.id} changed their membership status from ${previousValue} to ${value}.`)
      // Here, you can implement actions that could track conversions from one tier to another
    }
  }],
}
20}

In this example, the afterChange hook is used with a membershipStatusField, which allows users to select their membership level (Standard, Premium, VIP). The hook monitors changes in the membership status. When a change occurs, it logs the update and can be used to trigger further actions, such as tracking conversion from one tier to another or notifying them about changes in their membership benefits.

afterRead

The afterRead hook is invoked after a field value is read from the database. This is ideal for formatting or transforming the field data for output.

1import { Field } from 'payload/types'
2
3const dateField: Field = {
4  name: 'createdAt',
5  type: 'date',
6  hooks: {
7    afterRead: [({ value }) => {
8      // Format date for display
9      return new Date(value).toLocaleDateString()
10    }],
11  }
12}

Here, the afterRead hook for the dateField is used to format the date into a more readable format using toLocaleDateString(). This hook modifies the way the date is presented to the user, making it more user-friendly.

TypeScript

Payload exports a type for field hooks which can be accessed and used as follows:

1import type { FieldHook } from 'payload/types'
2
3// Field hook type is a generic that takes three arguments:
4// 1: The document type
5// 2: The value type
6// 3: The sibling data type
7
8type ExampleFieldHook = FieldHook<ExampleDocumentType, string, SiblingDataType>
9
10const exampleFieldHook: ExampleFieldHook = (args) => {
11  const {
12    value, // Typed as `string` as shown above
13    data, // Typed as a Partial of your ExampleDocumentType
14    siblingData, // Typed as a Partial of SiblingDataType
15    originalDoc, // Typed as ExampleDocumentType
16    operation,
17    req,
18  } = args
19
20  // Do something here...
21
22  return value // should return a string as typed above, undefined, or null
23}

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