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Translation strategy

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

Steps

Creating a custom data source will require you to work on the 3 following steps:

  1. Declare the structure of the data

  2. Declare the API capabilities

  3. Code a translation layer

Minimal example

const { BaseCollection } = require('@forestadmin/datasource-toolkit');
const axios = require('axios'); // client for the target API

// The real work is in writing this module
// Expect a full featured query translation module to be over 1000 LOCs
const QueryGenerator = require('./forest-query-translation');

/** Minimal implementation of a readonly data source */
class MyCollection extends BaseCollection {
  constructor() {
    // Set name of the collection once imported
    super('myCollection');

    this.addField('id', {
      // Structure
      type: 'Column',
      columnType: 'Number',
      isPrimaryKey: true,
      isReadOnly: true, // field is readonly

      // As we are using the query translation strategy => define capabilities
      filterOperators: new Set(), // field is not filterable
      isSortable: false, // field is not sortable
    });

    this.addField('title', {
      type: 'Column',
      columnType: 'String',
      isReadOnly: true,
      filterOperators: new Set(),
      isSortable: false,
    });
  }

  async list(filter, projection) {
    const params = QueryGenerator.generateListQueryString(filter, projection);
    const response = axios.get('https://my-api/my-collection', { params });

    return response.body.items;
  }

  async aggregate(filter, aggregation, limit) {
    const params = QueryGenerator.generateAggregateQueryString(filter, projection);
    const response = axios.get('https://my-api/my-collection', { params });

    return response.body.items;
  }
}

class MyDataSource extends BaseDataSource {
  constructor() {
    super(
      [new MyCollection(this)], // List of your collections
    );
  }
}

module.exports = MyDataSource;
const MyDataSource = require('./datasource');

const myDataSourceFactory = async () => new MyDataSource();

const agent = createAgent(options).addDataSource(myDataSourceFactory);

Read more

Implementing a data source using the "query translation" strategy is an advanced concept: you will need to have a deep understanding of Forest Admin internals.

This strategy is a good match when writing data sources for full-featured databases.

Before starting, it is highly advised to read and understand the following sections:

PreviousWrite handlersNextStructure declaration

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