Intra-data source Relationships

We've seen that when building data sources, collections must fulfill the contract they defined when declaring their capabilities.

The same is also true for Intra-data source relationships which are declared on the structure of a collection: declared relations must be handled when processing filters, projection, and aggregations.

In practice

one-to-many and many-to-many relationships do not require additional work: Forest Admin will automatically call the destination collection with a valid filter.

On the other hand, many-to-one and one-to-one relationships require the implementer to make all fields from the target collection available on the source collection (under a prefix).

Example

If a structure declaration contains the following statement

class MovieCollection extends BaseCollection {
  constructor() {
    super('movies');

    // [...]

    this.addField('director', {
      type: 'ManyToOne',
      foreignCollection: 'people',
      foreignKey: 'directorId',
      foreignKeyTarget: 'id',
    });
  }
}

Then the collection must accept references to fields from the people collection under the director prefix in all method parameters.

// The following call is using both fields from the "movies" and "people" collection
await dataSource.getCollection('movies').list(
  {
    conditionTree: {
      aggregator: 'And',
      conditions: [
        { field: 'title', operator: 'Equal', value: 'E.T.' },
        { field: 'director:firstName', operator: 'Equal', value: 'Stephen' },
      ]
    }.
    sort: [{ field: 'director:birthDate', ascending: true }]
  },
  ['id', 'title', 'director:firstName', 'director:lastName']
);

should return

{
  "id": 34,
  "title": "E.T",
  "director": { "firstName": "Stephen", "lastName": "Spielberg" }
}