Easily define parameter structure and validate/cast with Ecto.Schema
Available in Hex, the package can be installed as:
Add params to your list of dependencies in mix.exs:
def deps do
[
{:params, "~> 2.0"}
]
endIf you've been doing Ecto based applications lately, you know Ecto provides a very easy way to populate structs with data coming from request parameters, validating and casting their values along the way.
All this thanks to the Ecto.Schema and Ecto.Changeset modules. The first specifies the fields your model has (typically the same as your db table) and the later provides an easy way to convert potentially unsafe data and validate stuff via changesets.
So for example, in a typical Phoenix application, a User model
would look like:
defmodule MyApp.User do
use MyApp.Web, :model
schema "users" do
field :name, :string
field :age, :integer
end
@required [:name]
@optional [:age]
def changeset(changeset_or_model, params) do
cast(changeset_or_model, params, @required ++ @optional)
|> validate_required(@required)
end
endNormally, changesets are related to some data that will be persisted into
a database, and your controller would use the User.changeset method like:
# UserController.ex
def create(conn, params) do
ch = User.changeset(%User{}, params)
if ch.valid? do
...
end
However, you can use Ecto.Schema for validating/casting data that
won't necessarily be persisted into a database. All you need is just specify a module and
define your schema, Ecto.Changeset will be happy to work with it.
This comes handy when you have certain parameter structure you want to enforce for example when creating a REST API.
Some Rails developers might be right now wondering where their
strong parameters can be defined. On Elixir land, there's no need for such a thing, as we will see, just using an Ecto.Schema with Ecto.Changeset
can be much more flexible. Using schemas allows not only
specifying which fields we want, but changesets let use
type cast, perform validations on values, etc.
So, for example, suppose your Phoenix based API performs a search for kittens looking for a home and expects something like:
{
"breed": "Russian Blue",
"age_min": 0,
"age_max": 5,
"near_location": {
"latitude": 92.1,
"longitude": -82.1
}
}You'd like to validate that your controller has received the correct params structure, all you need to do is create a couple of modules:
defmodule MyApi.Params.Location
use Ecto.Schema
import Ecto.Changeset
@required ~w(latitude longitude)
@optional ~w()
schema "location params" do
field :latitude, :float
field :longitude, :float
end
def changeset(ch, params) do
cast(ch, params, @required ++ @optional)
|> validate_required(@required)
end
end
defmodule MyAPI.Params.KittenSearch
use Ecto.Schema
import Ecto.Changeset
@required ~w(breed)
@optional ~w(age_min age_max)
schema "params for kitten search" do
field :breed, :string
field :age_min, :integer
field :age_max, :integer
field :age_max, :integer
field :color, Ecto.Enum, values: [:brown, :black, :grey, :unknown],
embeds_one :near_location, Location
end
def changeset(ch, params) do
cast(ch, params, @required ++ @optional)
|> validate_required(@required)
|> cast_embed(:near_location, required: true)
end
end
# On your controller:
def search(conn, params) do
alias MyAPI.Params.KittenSearch
changeset = KittenSearch.changeset(%KittenSearch{}, params)
if changeset.valid? do
...
end
That would allow you to take only valid params as you'd normally have with any other Ecto.Schema module.
However it's still a lot of code, most of it defining the the changeset, specifying the optional and required fields, etc.
Params is just a simple Ecto.Schema wrapper for reducing all this boilerplate, while still leting you create custom changesets for parameter processing.
The previous example could be written like:
defmodule MyAPI.KittenController do
use Params
defparams kitten_search %{
breed!: :string,
age_max: :integer,
age_min: [field: :integer, default: 1],
color: [field: Ecto.Enum, values: [:brown, :black, :grey, :unknown]],
near_location!: %{
latitude!: :float, longitude!: :float
},
tags: [:string]
}
def index(conn, params) do
changeset = kitten_search(params)
if changeset.valid? do
search = Params.data changeset
IO.puts search.near_location.latitude
...
end
end
The defparams macro generates a module for processing
a params schema
By default all fields are optional. You can mark
required fields by ending them with a !, of course
the bang is removed from the field definition and is
only used to mark which fields are required by default.
You can also create a module and define your schema or custom changesets in it:
defmodule UserSearch do
use Params.Schema, %{name: :string, age: :integer}
import Ecto.Changeset, only: [cast: 3, validate_inclusion: 3]
def child(ch, params) do
cast(ch, params, ~w(name age))
|> validate_inclusion(:age, 1..6)
end
end
defmodule MyApp.UserController do
def index(conn, params) do
changeset = UserSearch.from(params, with: &UserSearch.child/2)
if changeset.valid? do
# age in 1..6
end
end
The Params.data and Params.to_map can be useful for obtaining a struct or map from a changeset.
Note that Params.data and Params.to_map have different behaviour: data
returns a struct which will include all valid params. to_map returns a map
that only includes the submitted keys and keys with default values:
defmodule UserUpdateParams do
use Params.Schema, %{
name: :string,
age: :integer,
auditlog: [field: :boolean, default: true]
}
end
changeset = UserUpdateParams.from(%{name: "John"})
Params.data(changeset) # => %UserUpdateParams{name: "John", age: nil, auditlog: true}
Params.to_map(changeset) # => %{name: "John", auditlog: true}Here's a list of awesome people who have contributed code to this project.
If you find a bug or want to improve something, please send a pull-request. Thank you!
Copyright (c) 2016 Victor Hugo Borja
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at https://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
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