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try JSON Schema with my new personal project, and was disappointed to see the top Google result is a few specifications out-of-date.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!

The Xema library was updated to 0.8.0 and works now with inlined references to speed up validation. That also affects JsonXema see benchmark.

Xema also supports now custom validators. There is an example on the examples page in the online docs.

The new release of Xema adds the macros field and required to create struct schemas.

iex> defmodule StructA do
...>   use Xema
...>
...>   xema do
...>     field :foo, :integer, minimum: 0
...>   end
...> end
...>
...> defmodule StructB do
...>   use Xema
...>
...>   xema do
...>     field :a, :string, min_length: 3
...>     field :b, StructA
...>     required [:a]
...>   end
...> end
...>
...> data = StructB.cast!(a: "abc", b: %{foo: 5})
...> data.a
"abc"
iex> Map.from_struct(data.b)
%{foo: 5}

A more extensive example can be found at Examples > Struct