cdac24c79f
What is the `Cacheable` type class about? ```haskell class Eq a => Cacheable a where unchanged :: Accesses -> a -> a -> Bool default unchanged :: (Generic a, GCacheable (Rep a)) => Accesses -> a -> a -> Bool unchanged accesses a b = gunchanged (from a) (from b) accesses ``` Its only method is an alternative to `(==)`. The added value of `unchanged` (and the additional `Accesses` argument) arises _only_ for one type, namely `Dependency`. Indeed, the `Cacheable (Dependency a)` instance is non-trivial, whereas every other `Cacheable` instance is completely boilerplate (and indeed either generated from `Generic`, or simply `unchanged _ = (==)`). The `Cacheable (Dependency a)` instance is the only one where the `Accesses` argument is not just passed onwards. The only callsite of the `unchanged` method is in the `ArrowCache (Rule m)` method. That is to say that the `Cacheable` type class is used to decide when we can re-use parts of the schema cache between Metadata operations. So what is the `Cacheable (Dependency a)` instance about? Normally, the output of a `Rule m a b` is re-used when the new input (of type `a`) is equal to the old one. But sometimes, that's too coarse: it might be that a certain `Rule m a b` only depends on a small part of its input of type `a`. A `Dependency` allows us to spell out what parts of `a` are being depended on, and these parts are recorded as values of types `Access a` in the state `Accesses`. If the input `a` changes, but not in a way that touches the recorded `Accesses`, then the output `b` of that rule can be re-used without recomputing. So now you understand _why_ we're passing `Accesses` to the `unchanged` method: `unchanged` is an equality check in disguise that just needs some additional context. But we don't need to pass `Accesses` as a function argument. We can use the `reflection` package to pass it as type-level context. So the core of this PR is that we change the instance declaration from ```haskell instance (Cacheable a) => Cacheable (Dependency a) where ``` to ```haskell instance (Given Accesses, Eq a) => Eq (Dependency a) where ``` and use `(==)` instead of `unchanged`. If you haven't seen `reflection` before: it's like a `MonadReader`, but it doesn't require a `Monad`. In order to pass the current `Accesses` value, instead of simply passing the `Accesses` as a function argument, we need to instantiate the `Given Accesses` context. We use the `give` method from the `reflection` package for that. ```haskell give :: forall r. Accesses -> (Given Accesses => r) -> r unchanged :: (Given Accesses => Eq a) => Accesses -> a -> a -> Bool unchanged accesses a b = give accesses (a == b) ``` With these three components in place, we can delete the `Cacheable` type class entirely. The remainder of this PR is just to remove the `Cacheable` type class and its instances. PR-URL: https://github.com/hasura/graphql-engine-mono/pull/6877 GitOrigin-RevId: 7125f5e11d856e7672ab810a23d5bf5ad176e77f |
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Hasura GraphQL Engine
Hasura is an open-source product that accelerates API development by 10x by giving you GraphQL or REST APIs with built-in authorization on your data, instantly.
Read more at hasura.io and the docs.
Features
- Make powerful queries: Built-in filtering, pagination, pattern search, bulk insert, update, delete mutations
- Works with existing, live databases: Point it to an existing database to instantly get a ready-to-use GraphQL API
- Realtime: Convert any GraphQL query to a live query by using subscriptions
- Merge remote schemas: Access custom GraphQL schemas for business logic via a single GraphQL Engine endpoint. Read more.
- Extend with Actions: Write REST APIs to extend Hasura’s schema with custom business logic.
- Trigger webhooks or serverless functions: On Postgres insert/update/delete events (read more)
- Scheduled Triggers: Execute custom business logic at specific points in time using a cron config or a one-off event.
- Fine-grained access control: Dynamic access control that integrates with your auth system (eg: auth0, firebase-auth)
- Admin UI & Migrations: Admin UI & Rails-inspired schema migrations
- Supported Databases: Supports PostgreSQL (and its flavors), MS SQL Server and Big Query. Support for more databases coming soon.
Read more at hasura.io and the docs.
Table of contents
Table of Contents
- Quickstart:
- Architecture
- Client-side tooling
- Add business logic
- Demos
- Support & Troubleshooting
- Stay up to date
- Contributing
- Brand assets
- License
- Translations
Quickstart:
One-click deployment on Hasura Cloud
The fastest and easiest way to try Hasura out is via Hasura Cloud.
-
Click on the following button to deploy GraphQL engine on Hasura Cloud including Postgres add-on or using an existing Postgres database:
-
Open the Hasura console
Click on the button "Launch console" to open the Hasura console.
-
Make your first GraphQL query
Create a table and instantly run your first query. Follow this simple guide.
Other one-click deployment options
Check out the instructions for the following one-click deployment options:
| Infra provider | One-click link | Additional information |
|---|---|---|
| Heroku |  |
docs |
| DigitalOcean |  |
docs |
| Azure |  |
docs |
| Render |  |
docs |
Other deployment methods
For Docker-based deployment and advanced configuration options, see deployment guides or install manifests.
Architecture
The Hasura GraphQL Engine fronts a Postgres database instance and can accept GraphQL requests from your client apps. It can be configured to work with your existing auth system and can handle access control using field-level rules with dynamic variables from your auth system.
You can also merge remote GraphQL schemas and provide a unified GraphQL API.
Client-side tooling
Hasura works with any GraphQL client. See awesome-graphql for a list of clients. Our frontend tutorial series also have integrations with GraphQL clients for different frameworks.
Add business logic
GraphQL Engine provides easy-to-reason, scalable and performant methods for adding custom business logic to your backend:
Remote schemas
Add custom resolvers in a remote schema in addition to Hasura's database-based GraphQL schema. Ideal for use-cases like implementing a payment API, or querying data that is not in your database - read more.
Actions
Actions are a way to extend Hasura’s schema with custom business logic using custom queries and mutations. Actions can be added to Hasura to handle various use cases such as data validation, data enrichment from external sources and any other complex business logic - read more
Trigger webhooks on database events
Add asynchronous business logic that is triggered based on database events. Ideal for notifications, data-pipelines from Postgres or asynchronous processing - read more.
Derived data or data transformations
Transform data in Postgres or run business logic on it to derive another dataset that can be queried using GraphQL Engine - read more.
Demos
Check out all the example applications in the community/sample-apps directory.
Realtime applications
-
Group Chat application built with React, includes a typing indicator, online users & new message notifications.
-
Live location tracking app that shows a running vehicle changing the current GPS coordinates moving on a map.
-
A real-time dashboard for data aggregations on continuously changing data.
Videos
- Add GraphQL to a self-hosted GitLab instance (3:44 mins)
- Todo app with Auth0 and GraphQL backend (4:00 mins)
- GraphQL on GitLab integrated with GitLab auth (4:05 mins)
- Dashboard for 10million rides with geo-location (PostGIS, Timescale) (3:06 mins)
Support & Troubleshooting
The documentation and community will help you troubleshoot most issues. If you have encountered a bug or need to get in touch with us, you can contact us using one of the following channels:
- Support & feedback: Discord
- Issue & bug tracking: GitHub issues
- Follow product updates: @HasuraHQ
- Talk to us on our website chat
We are committed to fostering an open and welcoming environment in the community. Please see the Code of Conduct.
If you want to report a security issue, please read this.
Stay up to date
We release new features every month. Sign up for our newsletter by using the link below. We send newsletters only once a month. https://hasura.io/newsletter/
Contributing
Check out our contributing guide for more details.
Brand assets
Hasura brand assets (logos, the Hasura mascot, powered by badges etc.) can be found in the assets/brand folder. Feel free to use them in your application/website etc. We'd be thrilled if you add the "Powered by Hasura" badge to your applications built using Hasura. ❤️
<!-- For light backgrounds -->
<a href="https://hasura.io">
<img width="150px" src="https://graphql-engine-cdn.hasura.io/img/powered_by_hasura_primary_darkbg.svg" />
</a>
<!-- For dark backgrounds -->
<a href="https://hasura.io">
<img width="150px" src="https://graphql-engine-cdn.hasura.io/img/powered_by_hasura_primary_lightbg.svg" />
</a>
License
The core GraphQL Engine is available under the Apache License 2.0 (Apache-2.0).
All other contents (except those in server, cli and
console directories) are available under the MIT License.
This includes everything in the docs and community
directories.
Translations
This readme is available in the following translations:
- Japanese 🇯🇵 (🙏 @moksahero)
- French 🇫🇷 (🙏 @l0ck3)
- Bosnian 🇧🇦 (🙏 @hajro92)
- Russian 🇷🇺 (🙏 @highflyer910)
- Greek 🇬🇷 (🙏 @MIP2000)
- Spanish 🇲🇽(🙏 @ferdox2)
- Indonesian 🇮🇩 (🙏 @anwari666)
- Brazilian Portuguese 🇧🇷 (🙏 @rubensmp)
- German 🇩🇪 (🙏 @FynnGrandke)
- Chinese 🇨🇳 (🙏 @jagreetdg & @johnbanq)
- Turkish 🇹🇷 (🙏 @berat)
- Korean 🇰🇷 (🙏 @라스크)
- Italian 🇮🇹 (🙏 @befire)
Translations for other files can be found here.