# `JSONAPIPlug.QueryParser`
[🔗](https://github.com/lucacorti/jsonapi_plug/blob/main/lib/jsonapi_plug/query_parser.ex#L1)

Parses a JSON:API query parameter to a user defined format.

You can implement a custom format for `JSON:API` query parameters that do not define
a standard format: filter, page and sort.

To customize the default parser implement a module adopting the `JSONAPIPlug.QueryParser`
behaviour for your sort format:

```elixir
defmodule MyApp.API.QueryParsers.Sort do
  ...
  @behaviour JSONAPIPlug.QueryParser

  # Transforms the query parameter value to a user defined format
  @impl JSONAPIPlug.QueryParser
  def parse(jsonapi_plug, sort) do
    ...my sort query parameter parsing logic...
  end
end
```

and configure it in your API configuration under the `parsers` key.

```elixir
config :my_app, MyApp.API,
  parsers: [
    filter: MyApp.API.QueryParser.Filter,
    page: MyApp.API.QueryParser.Page,
    sort: MyApp.API.QueryParser.Sort
  ]
```

The parsers take the query parameter value as input and its return value is placed under an
attribute with the same name as the query parameter in the `JSONAPIPlug` structure in the conn
`private` assigns so that you can retrieve it and use it in your application logic.

You can return a standard `JSON:API` error to the client by raising `JSONAPIPlug.Exceptions.InvalidQuery`
exception at any point in your parser code.

# `parse`

```elixir
@callback parse(JSONAPIPlug.t(), Plug.Conn.query_param()) :: term() | no_return()
```

Transforms the value of the JSON:API 'filter' query parameter

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*Consult [api-reference.md](api-reference.md) for complete listing*