I’d be interested in seeing a side-by-side comparison between Xema and Ecto’s validation.

Xema 0.9.0 is released. The new version comes with some breaking changes, see changelog.

New features

• convert data with Xema.cast
• nice error messages

Example:

iex> defmodule Person do
...>   use Xema
...>
...>   xema do
...>     map(
...>       keys: :atoms,
...>       properties: %{
...>         name: string(),
...>         age: integer(minimum: 0),
...>         fav: atom(enum: [:erlan, :elixir, :js, :rust, :go])
...>       }
...>     )
...>   end
...>
...>   def new(args), do: cast!(args)
...> end
iex>
iex> person = Person.new(name: "Joe", age: 24, fav: :elixir) 
%{
  age: 24,
  fav: :elixir,
  name: "Joe"
}
iex> json = person |> Jason.encode!() |> Jason.decode()
%{
  "age" => 24,
  "fav" => "elixir",
  "name" => "Joe"
}
iex> Person.cast!(json)
%{
  age: 24,
  fav: :elixir,
  name: "Joe"
}
iex> {:error, error} = Person.validate(%{name: 42, age: -1, fav: :php})
iex> Exception.message(error) 
"""
Value -1 is less than minimum value of 0, at [:age].
Value :php is not defined in enum, at [:fav].
Expected :string, got 42, at [:name].\
"""

More examples can be found at section Cast and Examples - Cast JSON.

Thanks for working on this! I wanted to try JSON Schema with my new personal project, and was disappointed to see the top Google result is a few specifications out-of-date. Glad I searched here on the forum!