Node.js Developer Guide
Other documentationsDemoCommunityGitHub
  • Forest Admin
  • Getting started
    • How it works
    • Quick start
    • Install
      • Create your agent
      • Expose an HTTP endpoint
        • For standalone agents
        • On Express
        • On Koa
        • On Fastify
        • On NestJS
      • Autocompletion & Typings
      • Troubleshooting
    • Migrating legacy agents
      • What's new
      • Pre-requisites
      • Recommendations
      • Migration steps
        • Run new agent in parallel
        • Configure database connection
        • Code transformations
          • API Charts
          • Live Queries
          • Smart Charts
          • Route overrides
          • Smart Actions
          • Smart Fields
          • Smart Relationships
          • Smart Segments
        • Compare schemas
        • Swap agents
      • Post-migration
        • Dropping Sequelize
        • Optimize your agent
  • Data Sources
    • Getting Started
      • Collection selection
      • Naming conflicts
      • Cross-data source relationships
      • Query interface and Native Queries
        • Fields and projections
        • Filters
        • Aggregations
    • Provided data sources
      • SQL (without ORM)
      • Sequelize
      • Mongoose
      • MongoDB
    • Write your own
      • Replication strategy
        • Persistent cache
        • Updating the replica
          • Scheduled rebuilds
          • Change polling
          • Push & Webhooks
        • Schema & References
        • Write handlers
      • Translation strategy
        • Structure declaration
        • Capabilities declaration
        • Read implementation
        • Write implementation
        • Intra-data source Relationships
      • Contribute
  • Agent customization
    • Getting Started
    • Actions
      • Scope and context
      • Result builder
      • Static Forms
      • Widgets in Forms
      • Dynamic Forms
      • Form layout customization
      • Related data invalidation
    • Charts
      • Value
      • Objective
      • Percentage
      • Distribution
      • Leaderboard
      • Time-based
    • Fields
      • Add fields
      • Move, rename and remove fields
      • Override binary field mode
      • Override writing behavior
      • Override filtering behavior
      • Override sorting behavior
      • Validation
    • Hooks
      • Collection hook
      • Collection override
    • Pagination
    • Plugins
      • Provided plugins
        • AWS S3
        • Advanced Export
        • Flattener
      • Write your own
    • Relationships
      • To a single record
      • To multiple records
      • Computed foreign keys
      • Under the hood
    • Search
    • Segments
  • Frontend customization
    • Smart Charts
      • Create a table chart
      • Create a bar chart
      • Create a cohort chart
      • Create a density map
    • Smart Views
      • Create a Map view
      • Create a Calendar view
      • Create a Shipping view
      • Create a Gallery view
      • Create a custom tinder-like validation view
      • Create a custom moderation view
  • Deploying to production
    • Environments
      • Deploy on AWS
      • Deploy on Heroku
      • Deploy on GCP
      • Deploy on Ubuntu
      • Deploy on Azure
    • Development workflow
    • Using branches
    • Deploying your changes
    • Forest Admin CLI commands
      • init
      • login
      • branch
      • switch
      • set-origin
      • push
      • environments:create
      • environments:reset
      • deploy
  • Under the hood
    • .forestadmin-schema.json
    • Data Model
      • Typing
      • Relationships
    • Security & Privacy
Powered by GitBook
On this page
  • How does it work
  • Making a field read-only
  • Examples

Was this helpful?

  1. Agent customization
  2. Fields

Override writing behavior

PreviousOverride binary field modeNextOverride filtering behavior

Last updated 1 year ago

Was this helpful?

This is the official documentation of the @forestadmin/agent Node.js agent.

Forest Admin allows replacing the default field writing behavior with your own custom logic.

This is useful when you want to change how a given field behaves, but also to make writable.

How does it work

The replaceFieldWriting function allows to change the behavior of any change by creating a new patch that will be applied to the record.

You should refrain from using handlers that have side effects (to perform error handling, validation, ...) and .

Making a field read-only

Can be achieved without any code .

Examples

Changing other fields in the same record

In the following example, editing or creating a fullName will update both firstName and lastName fields of the record.

collection.replaceFieldWriting('fullName', value => {
  const [firstName, lastName] = value.split(' ');

  return { firstName, lastName };
});

Having specific behavior only for updates

You can have different behavior for creations and updates.

In this example, each time the firstName field is edited, we also want to update a timestamp field.

collection.replaceFieldWriting('firstName', async (value, context) => {
  switch (context.action) {
    case 'create':
      return { firstName, firstNameLastEdited: null };

    case 'update':
      return { firstName, firstNameLastEdited: new Date().toISOString() };

    default:
      throw new Error('Unexpected value');
  }
});

Changing fields in related records

Handling relationships inside a replaceFieldWriting will only work for ManyToOne and OneToOne relationships.

In this simple example, we have two collections that are linked together:

  • The Users collection has a job and a portfolioId as foreignKey

  • The Portfolios collection has a title

When the user updates his job field we want also to update the title of the portfolio by the job name.

collection.replaceFieldWriting('job', (job, { action }) => {
  return { job, portfolio: { title: job } };
});

If the relationships do not exist it will create them with the given field values.

You can also provide another portfolioId to update the relationships and their fields:

collection.replaceFieldWriting('job', (job, { action }) => {
  return { job, portfolioId: 8, portfolio: { title: job } };
});

Of course, you can chain the relationships. For example, if a portfolio has a one-to-one relationship with the formats collection, you can update it by writing the right path.

collection.replaceFieldWriting('job', (job, { action }) => {
  return { job, portfolioId: 8, portfolio: { title: job, format: { name: 'pdf' } } };
});
computed fields
use hooks instead
in the field settings ↗