# Para
Para is an Elixir library that provides structured and declarative way of validating HTTP parameters.
Para uses Ecto under the hood and therefore inherits most of its utilities such as changeset and built-in validators.
### Why use Para?
When building API endpoints that deal with a lot of parameters, it is sometimes not enough to just rely on Ecto schema for parsing and validation. A lot of times the HTTP parameters do not always represent the final form of the data that gets sent to the database.
Para is meant to be implemented as part of your data processing pipeline, typically between external source to internal services. Using Para in this way avoids having to contaminate your controllers and internal services with repetitive inputs parsing and validations. It should also make testing a lot easier.
### Usage
Add Para as a dependency in your `mix.exs` file.
```
def deps do
[{:para, "~> 0.1"}]
end
```
After you are done, run `mix deps.get` in your shell to fetch and compile Para.
### Examples
First, let's define your parameters schema
```elixir
defmodule Web.FooPara do
use Para
validator :create do
required :name, :string
required :age, :integer
required :email, :string
optional :phone, :string
end
validator :update do
optional :name, :string
optional :age, :integer
optional :email, :string
optional :phone, :string
end
end
```
You can now use this module as a validator in your controller
```elixir
defmodule Web.FooController do
use Web, :schema
alias Web.FooPara
def create(conn, params) do
with {:ok, data} <- FooPara.validate(:create, params) do
# ...
end
end
def update(conn, params) do
with {:ok, data} <- FooPara.validate(:update, params) do
# ...
end
end
end
```
For more advanced usage, please refer to the [docs](https://hexdocs.pm/para/api-reference.html)
