forma v0.4.0 Forma View Source
Applies typespecs to JSON-like data.
This module can parse JSON-like data (such as maps with key strings) into a more structured form by trying to map it to conform to a module’s typespec.
This can generally be useful when interfacing with external data sources that provide you data as JSON or MessagePack, but that you wish to transform into either proper structs or richer data types without a native JSON representation (such as dates or sets) in your application.
It is heavily inspired by Go’s way of dealing with JSON data.
defmodule User do
defstruct [:id, :name, :age, :gender]
@type t :: %__MODULE__{
id: String.t,
name: String.t,
age: non_neg_integer(),
gender: :male | :female | :other | :prefer_not_to_say
}
end
Forma.parse(%{"id" => "1", "name" => "Fredrik", "age" => 30, "gender" => "male"}, User)
# => %User{id: "1", name: "Fredrik", age: 30, gender: :male}
Forma tries to figure out how to translate its input to a typespec. However, not all types have natural representations in JSON, for example dates, or don’t want to expose their internals (opaque types).
If you’re in control of the module defining the type, you can implement the __forma__/2
function to handle parsing input to your desired type
defmodule App.Date do
@opaque t :: Date
# first argument is the type to be parsed in this module
def __forma__(:t, input) do
case Date.from_iso8601(input) do
{:ok, date} -> date
{:error, reason} -> raise reason
end
end
end
If you’re not in control of the module, you can pass a parser along as an optional argument,
defmodule LogRow do
defstruct [:log, :timestamp]
type t :: %__MODULE__{
log: String.t,
timestamp: NaiveDateTime.t
}
end
Forma.parse(%{"log" => "An error occurred", "timestamp" => "2015-01-23 23:50:07"},
%{{NaiveDateTime, :t} => fn input ->
case NaiveDateTime.from_iso8601(input) do
{:ok, datetime} -> datetime
{:error, err} -> raise err
end
end})
The number of arguments to the parser functions depends on if the type is parameterized
or not (MapSet.t
vs MapSet.t(integer)
).
Link to this section Summary
Functions
Called when an application is started
Link to this section Types
Link to this section Functions
Called when an application is started.
This function is called when an application is started using
Application.start/2
(and functions on top of that, such as
Application.ensure_started/2
). This function should start the top-level
process of the application (which should be the top supervisor of the
application’s supervision tree if the application follows the OTP design
principles around supervision).
start_type
defines how the application is started:
:normal
- used if the startup is a normal startup or if the application is distributed and is started on the current node because of a failover from another node and the application specification key:start_phases
is:undefined
.{:takeover, node}
- used if the application is distributed and is started on the current node because of a failover on the nodenode
.{:failover, node}
- used if the application is distributed and is started on the current node because of a failover on nodenode
, and the application specification key:start_phases
is not:undefined
.
start_args
are the arguments passed to the application in the :mod
specification key (e.g., mod: {MyApp, [:my_args]}
).
This function should either return {:ok, pid}
or {:ok, pid, state}
if
startup is successful. pid
should be the PID of the top supervisor. state
can be an arbitrary term, and if omitted will default to []
; if the
application is later stopped, state
is passed to the stop/1
callback (see
the documentation for the c:stop/1
callback for more information).
use Application
provides no default implementation for the start/2
callback.
Callback implementation for Application.start/2
.