Setting up GraphQL schema using an existing database

When you have an existing database with a schema already present, you don’t need to create tables or views or run DDL queries through the Hasura console.

All you need to do is indicate to Hasura GraphQL engine which tables and views you want to expose over GraphQL and how they are connected to each other so that you can query them as a “graph”.

Step 1: Track tables/views

Tracking a table or a view means telling Hasura GraphQL engine that you want to expose that table/view over GraphQL.

To track a table or a view:

  1. Head to the Data -> Schema section of the console.
  2. Under the heading Untracked Tables/Views, click on the Add button next to the table/view name.

To track all tables and views present in the database:

  1. Head to the Data -> Schema section of the console.
  2. Under the heading Untracked Tables/Views, click the Add all button.

Step 2: Track foreign-keys

Tracking a foreign-key means creating a relationship between the tables involved in the foreign-key.

To track a foreign-key between two tables in the database:

  1. Head to the Data -> Schema section of the console.
  2. Click on a table involved in the foreign-key and head to the Relationships tab.
  3. You should see a suggested relationship based on the foreign-key. Click Add, give a name to your relationship (this will be the name of the nested object in the GraphQL query), and hit Save to create the relationship.
  4. Repeat with the other table involved in the foreign-key.

To track all the foreign-keys of all tables in the database:

  1. Head to the Data -> Schema section of the console.
  2. Under the heading Untracked Relations, click on the Track Available Relations to automatically create relationships based on the foreign-keys.

Note

In this case, Hasura GraphQL engine will automatically generate relationship names (the names of the nested objects in the GraphQL query) based on the table names and the foreign-key names. The name is generated in the following format:

  • For object relationships: Camel case of (foreignTableName + By + columnName)
  • For array relationships: Camel case of (foreignTableName + s + By + columnNameInForeignTable)

For example, for the foreign-key article::author_id -> author::id, the relationship names will be authorByAuthorId for article table and articlesByAuthorId for author table.

You can change the relationship names by heading to the Relationships tab of the concerned table and dropping and recreating the relationship with a name of your choice.