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  • 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)
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    • 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
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  • Count queries

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  1. Data Sources
  2. Write your own
  3. Translation strategy

Read implementation

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

Developing your query translation layer is much easier when you can preview your work and have intermediary deliverables.

Emulation comes to the rescue: all features that need to be implemented when making a translating data source can be emulated inside your Node.js, at the cost of performance.

This enables you to be up and running in minutes and then optimize your code as you go.

const { BaseCollection } = require('@forestadmin/datasource-toolkit');
const axios = require('axios');

/**
 * This collection will have terrible performance, but is perfect to test that the
 * structure declaration is well done.
 */
class MyCollection extends BaseCollection {
  // [... Declare structure and capabilities]

  async list(caller, filter, projection) {
    // Fetch all records on all requests (this is _very_ inefficient)
    const response = await axios.get('https://my-api/my-collection');
    const result = response.data.items;

    // Use "in-process emulation" for everything else.
    if (filter.conditionTree)
      result = filter.conditionTree.apply(result, this, caller.timezone);
    if (filter.sort) result = filter.sort.apply(result);
    if (filter.page) result = filter.page.apply(result);
    if (filter.segment)
      throw new Error('This collection does not implements native segments');
    if (filter.search) throw new Error('This collection is not natively searchable');

    return projection.apply(result);
  }

  async aggregate(caller, filter, aggregation, limit) {
    // Fetch all records which should be aggregated
    const records = await this.list(caller, filter, aggregation.projection);

    // Use "in-process emulation" to aggregate the results
    return aggregation.apply(records, caller.timezone, limit);
  }
}

Tips

Count queries

The aggregate method is used by Forest Admin both to count records and to extract the data which is needed to generate charts.

If the API/Database you are targeting has an efficient API that is made for counting records, you may want to handle this case first.

const { BaseCollection } = require('@forestadmin/datasource-toolkit');
const axios = require('axios');

 class MyCollection extends BaseCollection {
  // [... Declare structure, capabilities and list method]

  async aggregate(caller, filter, aggregation, limit) {
    const { operation, fields, groups } = aggregation;

    if (operation === 'Count' && groups.length === 0 && !field) {
      return [{ value: await this.count(caller, filter) }];
    }

    // [... handle the general case]
  }

  async count(caller, filter) {
    const response = await axios.get(
      `https://my-api/my-collection/count`,
      { params: { filter: this._translateFilter(caller, filter) } }
    );

    return response.data.count;
  }

  private _translateFilter(caller, filter) {
    // [... translate filter]
  }
}
PreviousCapabilities declarationNextWrite implementation

Last updated 4 months ago

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