Relationships Connect Data

Introduction

Relationships allow you to connect data, enabling you to query data across multiple entities.

Lifecycle

New to Hasura DDN?

If you haven't already, have a run through our Quickstart guide to set up your Hasura DDN instance. In the sections below, we'll guide you through how to interact with your metadata and shape your API to your liking!

Creating a relationship

To query data across multiple entities, you'll first need to create a relationship between them.

As an example, you can configure a relationship between a posts collection and a users collection. This assumes that both collections already have tracked models in your metadata, and that the Post model has a field called userId that matches values in the id field of User.

Create relationship in your metadata:

# We recommend adding this to the parent model's HML file
kind: Relationship
version: v1
definition:
  name: user
  source: Post
  target:
    model:
      name: User
      relationshipType: Object
  mapping:
    - source:
        fieldPath:
          - fieldName: userId
      target:
        modelField:
          - fieldName: id

Updating a relationship

Your underlying data source may change over time. You can update your relationship to reflect these changes.

For example, imagine you have a post-user relationship, and the posts previously used a field named userId. Now, however, that field name has changed to authorId.

First, update your connector configuration and models to reflect the changed field name.

Update your DataConnectorLink:

ddn connector-link update <connector_name> --subgraph <path_to_subgraph.yaml>

Then, update your model:

ddn model update <connector_name> users

Then edit the relationship configuration in subgraph metadata.

Edit the existing metadata file:

# In whichever HML file contains your relationship
kind: Relationship
version: v1
definition:
  name: user
  source: Post
  target:
    model:
      name: User
      relationshipType: Object
  mapping:
    - source:
        fieldPath:
          - fieldName: authorId # this is the line that has changed
      target:
        modelField:
          - fieldName: id

Deleting a relationship

If you no longer need a relationship, simply delete the metadata object.

Reference

You can learn more about relationships in the metadata reference docs.