Write your own

Custom data sources are the answer to the need to import collections from either

• Your in-house APIs.

• Unsupported databases.

• Unsupported SaaS providers.

Forest Admin is built so that it does not need to know the nature of the data source it is speaking to, as long as it exposes a given interface.

That interface is only there to abstract away differences between backends so that they can be used as forest admin collections. It was built to allow for the minimal feature set which allows forest admin to work.

Getting started

When creating a custom data source, you can use the "Query Translation" strategy:

-	Implement query translation
Recommended for	Databases or APIs with advanced query capabilities
How does it work	The data source translates all forest admin queries to the target API in real time.
Preconditions	Target API is capable of expressing filters, aggregating data, ...

Steps

Creating a custom data source will require you to work on the three 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 section:

• Data Model

  • Typing

  • Relationships

• Query interface

  • Fields and projections

  • Filters

  • Aggregations