You can expose VulcanizeDB data via [Postgraphile](https://github.com/graphile/postgraphile).
Check out [their documentation](https://www.graphile.org/postgraphile/) for the most up-to-date instructions on installing, running, and customizing Postgraphile.
## Simple Setup
As of April 30, 2019, you can run Postgraphile pointed at the default `vulcanize_public` database with the following commands:
-`--connection` specifies the database. The above command connects to the default `vulcanize_public` database defined in [the example config](../staging/environments/public.toml.example).
-`--schema` defines what schema(s) to expose. The above exposes the `public` schema (for core VulcanizeDB data) as well as a `custom` schema (where `custom` is the name of a schema defined in executed transformers).
-`--disable-default-mutations` prevents Postgraphile from exposing create, update, and delete operations on your data, which are otherwise enabled by default.
By default, Postgraphile will expose queries for all tables defined in your chosen database/schema(s), including [filtering](https://www.graphile.org/postgraphile/filtering/) and [auto-discovered relations](https://www.graphile.org/postgraphile/relations/).
If you'd like to expose more customized windows into your data, there are some techniques you can apply when writing migrations:
- [Computed columns](https://www.graphile.org/postgraphile/computed-columns/) enable you to derive additional fields from types defined in your database.
For example, you could write a function to expose a block header's state root over Postgraphile with a computed column - without modifying the `public.headers` table.
- [Custom queries](https://www.graphile.org/postgraphile/custom-queries/) enable you to provide on-demand access to more complex data (e.g. the product of joining and filtering several tables' data based on a passed argument).
For example, you could write a custom query to get the block timestamp for every transaction originating from a given address.
- [Subscriptions](https://www.graphile.org/postgraphile/subscriptions/) enable you to publish data as it is coming into your database.
The above list is not exhaustive - please see the Postgraphile documentation for a more comprehensive and up-to-date description of available features.
