Hi,
Assuming the following schema:
# user.ex
defmodule Schema.User do
@moduledoc false
use Ecto.Schema
import Ecto.Changeset
@required_params [:email, :password]
@optional_fields []
schema "users" do
has_many :orders, Schema.Order
embeds_one :profile, Schema.User.Profile
field :email, :string
field :password, :string, virtual: true
field :encrypted_password, :string
timestamps()
end
def changeset(user, params \\ %{}) do
user
|> cast(params, @required_params ++ @optional_fields)
|> validate_required(@required_params)
|> unique_constraint(:email, name: :unique_email)
|> validate_format(:email, ~r/\S+@\S+\.\S+/)
|> validate_length(:password, min: 6)
end
end
# user/profile.ex
defmodule Schema.User.Profile do
@moduledoc false
use Ecto.Schema
import Ecto.Changeset
@required_params [:first_name, :last_name, :gender, :phone]
@optional_fields [:image]
embedded_schema do
field :first_name, :string
field :last_name, :string
field :gender, :string
field :phone, :string
field :image, :string
end
def changeset(profile, params \\ %{}) do
profile
|> cast(params, @required_params ++ @optional_fields)
|> validate_required(@required_params)
end
end
# config.exs
use Mix.Config
config :persistence, Persistence.Repo,
adapter: Ecto.Adapters.MySQL,
database: "antidote",
username: "root",
password: System.get_env("DATABASE_PASSWORD"),
hostname: "localhost",
port: "3306"
iex >u = Schema.User.changeset(%Schema.User{}, %{:email => "contact@alexandrubagu.info", :password => "my_password"})
iex> p = Schema.User.Profile.changeset(%Schema.User.Profile{}, %{:first_name => "first", :last_name => "last_name", :gender => "m", :phone => "+40"})
iex >u = Ecto.Changeset.put_embed(u, :profile, p)
iex> Persistence.Repo.insert(u)
** (ArgumentError) application :ecto is not loaded, or the configuration parameter :json_library is not set
(elixir) lib/application.ex:261: Application.fetch_env!/2
lib/ecto/adapters/mysql/connection.ex:47: anonymous fn/1 in Ecto.Adapters.MySQL.Connection.map_params/1
(elixir) lib/enum.ex:1229: Enum."-map/2-lists^map/1-0-"/2
(elixir) lib/enum.ex:1229: Enum."-map/2-lists^map/1-0-"/2
lib/ecto/adapters/mysql/connection.ex:32: Ecto.Adapters.MySQL.Connection.execute/4
lib/ecto/adapters/sql.ex:235: Ecto.Adapters.SQL.sql_call/6
lib/ecto/adapters/mysql.ex:178: Ecto.Adapters.MySQL.insert/5
lib/ecto/repo/schema.ex:397: Ecto.Repo.Schema.apply/4
....
Because I use :map struct in MySQL, ecto it requires to define :json_library but I didn’t find the documentation for this.
Another solution is to define a custom type as it follows:
defmodule App.Types.JSON do
@behaviour Ecto.Type
def type, do: :json
def cast(any), do: {:ok, any}
def load(value), do: Poison.decode(value)
def dump(value), do: Poison.encode(value)
end
So, I want to know where/how can I define the :json_library if anyone knows 
Thanks 
