# Absinthe
A [GraphQL](https://facebook.github.io/graphql/) implementation for Elixir.
[](https://travis-ci.org/CargoSense/absinthe)
## Experimental!
Please note that this is an initial release, and while functional enough to
build basic APIs (we are using it in a production system), it should be
considered experimental. (Notably, it does not yet work with Relay.)
For more information on status, see [Specification Implementation](./README.md#specification-implementation), below.
## Goal
Absinthe's goal is full implementation of the specification--in as
idiomatic, flexible, and comfortable way possible.
### Working Features
- Basic query document execution and argument/field validation. (Note Validation
is currently done during Execution, rather than as a separate phase. This will
change in the next minor release.)
- Variables, including defaulting and `!` requirements.
- Full support for extending types, including scalars.
(See [Custom Types](./README.md#custom-types), below.)
- Argument and input object field deprecation. (See [Deprecation](./README.md#deprecation),
below.)
- Errors with source line numbers. (Someday, column numbers; the Leex lexer
doesn't support them yet.)
- An flexible adapter mechanism to translate between different naming
conventions (eg, `snake_case` and `camelCase`) in schema vs the client.
(See [Adapters](./README.md#adapters), below.).
### Notably Missing
Support for:
- Fragments and fragment spreads
- Directives
- Interfaces
- Comprehensive test suite against the specification (in progress under `test/specification`)
### Alternatives
You may also want to look at building from or using one of the following
alternatives.
* https://github.com/joshprice/graphql-elixir, with Plug support:
https://github.com/joshprice/plug_graphql
* https://github.com/asonge/graphql (Parser-only as of 2015-12)
## Installation
Install from [Hex.pm](https://hex.pm/packages/absinthe):
```elixir
def deps do
[{:absinthe, "~> 0.1.0"}]
end
```
Note: Absinthe requires Elixir 1.2.0-dev or higher.
## Learning GraphQL
For a grounding in GraphQL, I recommend you read through the following articles:
* The [GraphQL Introduction](https://facebook.github.io/react/blog/2015/05/01/graphql-introduction.html) and [GraphQL: A data query language](https://code.facebook.com/posts/1691455094417024/graphql-a-data-query-language/) posts from Facebook.
* The [Your First GraphQL Server](https://medium.com/@clayallsopp/your-first-graphql-server-3c766ab4f0a2#.m78ybemas) Medium post by Clay Allsopp. (Note this uses the [JavaScript GraphQL reference implementation](https://github.com/graphql/graphql-js).)
* Other blog posts that pop up. GraphQL is young!
* For the ambitious, the draft [GraphQL Specification](https://facebook.github.io/graphql/).
You may also be interested in how GraphQL is used by [Relay](https://facebook.github.io/relay/), a "JavaScript frameword for building data-driven React applications."
## Basic Usage
A GraphQL API starts by building a schema. Using Absinthe, schemas are normal
modules that use `Absinthe.Schema` and adhere to its behavior (ie, define at
least `query`).
For this example, we'll build a simple schema that allows users to look-up an
`item` by `id`, a required, non-null field of type `:id` (which is a built-in
type, just like `:string`, `:integer`, `:float`, and `:boolean`).
(You may want to refer to the [Absinthe API documentation](http://hexdocs.pm/absinthe)
for more detailed information as you look this over.)
```elixir
defmodule MyApp.Schema do
use Absinthe.Schema
alias Absinthe.Type
# Example data
@items %{
"foo" => %{id: "foo", name: "Foo"},
"bar" => %{id: "bar", name: "Bar"}
}
def query do
%Type.ObjectType{
fields: fields(
item: [
type: :item
args: args(
id: [type: non_null(:id)]
),
resolve: fn %{id: item_id}, _ ->
{:ok, @items[item_id]}
end
]
)
}
end
end
```
Some functions used here that are worth mentioning, pulled in automatically from
`Absinthe.Type.Definitions` by `use Absinthe.Schema`:
* `args()` and `fields()` are utility functions that reduce clutter in your
schema (by building maps of nicely-named `%Type.Argument{}` and
`%Type.FieldDefinition{}` structs, respectively, for you).
* `non_null()`: Used to add a non-null constraint to an argument. In this
example, we are requiring an `id` to be provided to resolve the `item` field.
You'll notice we mention another type here: `:item`.
We haven't defined that yet; let's do it. In the same `MyApp.Schema` module:
```elixir
@absinthe :type
def item do
%Type.ObjectType{
description: "An item",
fields: fields(
id: [type: :id],
name: [type: :string]
)
}
end
```
Some notes on defining types:
* By default, they will have the same atom identifier (eg, `:item`) as the
defining function. This can be overridden, eg, `@absinthe type: :my_custom_name`
* The `name` field of the `Type.ObjectType` struct is optional; if not provided,
it will be automatically set to a TitleCase version of the type identifier
(in this case, it's set to `"Item"`).
* You can define additional scalar types (including coercion logic); see
[Custom Types](./README.md#custom-types), below.
See [the documentation for Absinthe.Type.Definitions](http://hexdocs.pm/absinthe/Absinthe.Type.Definitions.html)
for more information.
Now, you can use Absinthe to execute a query document. Let's get the
item with ID `"foo"`:
```elixir
"""
{
item(id: "foo") {
name
}
}
"""
|> Absinthe.run(MyApp.Schema)
# Result
{:ok, %{data: %{"item" => %{"name" => "Foo"}}}}
```
We can also use a variable:
## Variables
To support variables, simply define them for your query document [as the specification expects](https://facebook.github.io/graphql/#sec-Language.Query-Document.Variables),
and pass in a `variables` option (eg, query parameters passed along with the
request) to `run`:
```elixir
"""
query GetItem($id: ID!) {
item(id: $id) {
name
}
}
"""
|> Absinthe.run(MyApp.Schema, variables: %{id: "bar"})
# Result
{:ok, %{data: %{"item" => %{"name" => "Bar"}}}}
```
## Deprecation
Use the `deprecate` function on an argument definition (or input object field),
passing an optional `reason`:
```elixir
def query do
%Type.ObjectType{
name: "RootQuery",
fields: fields(
item: [
type: :item
args: args(
id: [type: non_null(:id)],
oldId: deprecate([type: non_null(:string)],
reason: "It's old.")
),
resolve: fn %{id: item_id}, _ ->
{:ok, @items[item_id]}
end
]
)
}
end
```
`resolve` functions must accept 2 arguments: a map of arguments and a
special `%Absinthe.Execution{}` struct that provides the full execution context
(useful for advanced purposes). `resolve` functions must return a `{:ok, result}`
or `{:error, "Error to report"}` tuple.
Note: At the current time, Absinthe reports any deprecated argument or
deprecated input object field used in the `errors` entry of the response. Non
null constraints are ignored when validating deprecated arguments and input
object fields.
## Custom Types
Absinthe supports defining custom scalar types, just like the built-in types.
Here's an example of how to support a time scalar to/from ISOz format:
```elixir
@absinthe type: :iso_z
def iso_z_type do
%Type.Scalar{
name: "ISOz",
description: "ISOz time",
parse: &Timex.DateFormat.parse(&1, "{ISOz}"),
serialize: &Timex.DateFormat.format!(&1, "{ISOz}")
}
end
```
Now `:iso_z` can be used in your schema and variables can use
`ISOz` in query documents.
## Adapters
Absinthe supports an adapter mechanism that allows developers to define their
schema using one code convention (eg, `snake_cased` fields and arguments), but
accept query documents and return results (including names in errors) in
another (eg, `camelCase`). This is useful in allowing both client and server to
use conventions most natural to them.
Absinthe ships with two adapters:
* `Absinthe.Adapter.Passthrough`, which is a no-op adapter and makes no
modifications. (This is the default.)
* `Absinthe.Adapter.LanguageConventions`, which expects schemas to be defined
in `snake_case` (the standard Elixir convention), translating to/from `camelCase`
for incoming query documents and outgoing results.
To set the adapter, you can set an application configuration value:
```elixir
config :absinthe,
adapter: Absinthe.Adapter.LanguageConventions
```
Or, you can provide it as an option to `Absinthe.run/3`:
```elixir
Absinthe.run(query, MyApp.Schema,
adapter: Absinthe.Adapter.LanguageConventions)
```
Notably, this means you're able to switch adapters on case-by-case basis.
In a Phoenix application, this means you could even support using different
adapters for different clients.
A custom adapter module must merely implement the `Absinthe.Adapter` protocol,
in many cases with `use Absinthe.Adapter` and only overriding the desired
functions.
## Specification Implementation
Absinthe is currently targeting the [GraphQL Working Draft](https://facebook.github.io/graphql), dated October 2015.
Here's the basic status, using the following scale:
* *Missing*: Sorry, nothing done yet!
* *Partial*: Some work done. May be used in a limited, experimental fashion, but
some basic features may be missing.
* *Functional*: Functional for most uses, but more advanced features may be
missing, and only loosely adheres to [parts of] the specification.
* *Complete*: Work completed. Please report any mismatches against the
specification.
| Section | Implementation | Reference |
| ------------: | :------------- | :---------------------------------------------------------------------------------------- |
| Language | Functional | [GraphQL Specification, Section 2](https://facebook.github.io/graphql/#sec-Language) |
| Type System | Functional | [GraphQL Specification, Section 3](https://facebook.github.io/graphql/#sec-Type-System) |
| Introspection | Missing | [GraphQL Specification, Section 4](https://facebook.github.io/graphql/#sec-Introspection) |
| Validation | Partial | [GraphQL Specification, Section 5](https://facebook.github.io/graphql/#sec-Validation) |
| Execution | Functional | [GraphQL Specification, Section 6](https://facebook.github.io/graphql/#sec-Execution) |
| Response | Functional | [GraphQL Specification, Section 7](https://facebook.github.io/graphql/#sec-Response) |
### Roadmap & Contributions
For a list of specific planned features and version targets, see the
[milestone list](https://github.com/CargoSense/ex_graphql/milestones).
We welcome issues and pull requests; please see CONTRIBUTING.
## License
BSD License
Copyright (c) CargoSense, Inc.
Parser derived from GraphQL Elixir, Copyright (c) Josh Price
https://github.com/joshprice/graphql-elixir
Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright notice, this
list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation
and/or other materials provided with the distribution.
* Neither the name Facebook nor the names of its contributors may be used to
endorse or promote products derived from this software without specific
prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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