defmodule Absinthe.Adapter do
@moduledoc """
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`).
Adapters aren't a part of GraphQL, but a utility that Absinthe adds so that
both client and server can use use conventions most natural to them.
Absinthe ships with four adapters:
* `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. (This is the default as of v0.3.)
* `Absinthe.Adapter.Underscore`, which is similar to the `Absinthe.Adapter.LanguageConventions`
adapter but converts all incoming identifiers to underscores and does not
modify outgoing identifiers (since those are already expected to be
underscores). Unlike `Absinthe.Adapter.Passthrough` this does not break
introspection.
* `Absinthe.Adapter.Passthrough`, which is a no-op adapter and makes no
modifications. (Note at the current time this does not support introspection
if you're using camelized conventions).
* `Absinthe.Adapter.StrictLanguageConventions`, which expects schemas to be
defined in `snake_case`, translating to `camelCase` for outgoing results.
This adapter requires incoming query documents to use `camelCase`.
To set an adapter, you pass a configuration option at runtime:
For `Absinthe.run/3`:
```
Absinthe.run(
query,
MyApp.Schema,
adapter: YourApp.Adapter.TheAdapterName
)
```
For `Absinthe.Plug`:
```
forward "/api",
to: Absinthe.Plug,
init_opts: [schema: MyAppWeb.Schema, adapter: YourApp.Adapter.TheAdapterName]
```
For GraphiQL:
```
forward "/graphiql",
to: Absinthe.Plug.GraphiQL,
init_opts: [schema: MyAppWeb.Schema, adapter: YourApp.Adapter.TheAdapterName]
```
Check `Absinthe.Plug` for full documentation on using the Plugs
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.
## Writing Your Own
All you may need to implement in your adapter is `to_internal_name/2` and
`to_external_name/2`.
Check out `Absinthe.Adapter.LanguageConventions` for a good example.
Note that types that are defined external to your application (including
the introspection types) may not be compatible if you're using a different
adapter.
"""
@type t :: module
defmacro __using__(_) do
quote do
@behaviour unquote(__MODULE__)
def to_internal_name(external_name, _role) do
external_name
end
def to_external_name(internal_name, _role) do
internal_name
end
defoverridable to_internal_name: 2,
to_external_name: 2
end
end
@typedoc "The lexical role of a name within the document/schema."
@type role_t :: :operation | :field | :argument | :result | :type | :directive
@doc """
Convert a name from an external name to an internal name.
## Examples
Prefix all names with their role, just for fun!
```
def to_internal_name(external_name, role) do
role_name = role |> to_string
role_name <> "_" <> external_name
end
```
"""
@callback to_internal_name(binary | nil, role_t) :: binary | nil
@doc """
Convert a name from an internal name to an external name.
## Examples
Remove the role-prefix (the inverse of what we did in `to_internal_name/2` above):
```
def to_external_name(internal_name, role) do
internal_name
|> String.replace(~r/^\#{role}_/, "")
end
```
"""
@callback to_external_name(binary | nil, role_t) :: binary | nil
end