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A collection of handy Elixir macros for CQRS applications.
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lib/cqrs/bounded_context.ex
defmodule Cqrs.BoundedContext do
alias Cqrs.{BoundedContext, Guards}
@moduledoc """
Macros to create proxy functions to [commands](`Cqrs.Command`) and [queries](`Cqrs.Query`) in a module.
## Examples
defmodule Users do
use Cqrs.BoundedContext
command CreateUser
command CreateUser, as: :create_user2
query GetUser
query GetUser, as: :get_user2
end
### Commands
iex> {:error, {:invalid_command, state}} =
...> Users.create_user(name: "chris", email: "wrong")
...> state.errors
%{email: ["has invalid format"]}
iex> {:error, {:invalid_command, state}} =
...> Users.create_user2(name: "chris", email: "wrong")
...> state.errors
%{email: ["has invalid format"]}
iex> Users.create_user(name: "chris", email: "chris@example.com")
{:ok, :dispatched}
iex> Users.create_user2(name: "chris", email: "chris@example.com")
{:ok, :dispatched}
### Queries
iex> Users.get_user!()
** (Cqrs.QueryError) %{email: ["can't be blank"]}
iex> Users.get_user2!()
** (Cqrs.QueryError) %{email: ["can't be blank"]}
iex> Users.get_user!(email: "wrong")
** (Cqrs.QueryError) %{email: ["has invalid format"]}
iex> {:error, %{errors: errors}} = Users.get_user()
...> errors
[email: {"can't be blank", [validation: :required]}]
iex> {:error, %{errors: errors}} = Users.get_user(email: "wrong")
...> errors
[email: {"has invalid format", [validation: :format]}]
iex> {:ok, query} = Users.get_user_query(email: "chris@example.com")
...> query
#Ecto.Query<from u0 in User, where: u0.email == ^"chris@example.com">
iex> {:ok, user} = Users.get_user(email: "chris@example.com")
...> %{id: user.id, email: user.email}
%{id: "052c1984-74c9-522f-858f-f04f1d4cc786", email: "chris@example.com"}
"""
defmacro __using__(_) do
quote do
Module.register_attribute(__MODULE__, :queries, accumulate: true)
Module.register_attribute(__MODULE__, :commands, accumulate: true)
import BoundedContext, only: [command: 1, command: 2, query: 1, query: 2]
@before_compile BoundedContext
end
end
defmacro __before_compile__(_env) do
quote do
commands = Enum.map(@commands, &BoundedContext.__command_proxy__/1)
queries = Enum.map(@queries, &BoundedContext.__query_proxy__/1)
Module.eval_quoted(__ENV__, commands)
Module.eval_quoted(__ENV__, queries)
Module.delete_attribute(__MODULE__, :queries)
Module.delete_attribute(__MODULE__, :commands)
end
end
@doc """
Creates proxy functions to dispatch this command module.
## Functions created
When given `CreateUser`
* `create_user!/0`
* `create_user!/1`
* `create_user!/2`
* `create_user/0`
* `create_user/1`
* `create_user/2`
## Options
* `:after` - A function of one arity to run with the execution result.
"""
defmacro command(command_module, opts \\ []) do
quote location: :keep do
Guards.ensure_is_command!(unquote(command_module))
function_name = BoundedContext.__function_name__(unquote(command_module), unquote(opts))
then =
case Keyword.get(unquote(opts), :after, []) do
[] -> &Function.identity/1
fun when is_function(fun, 1) -> fun
list when is_list(list) -> Keyword.get(list, function_name, &Function.identity/1)
end
@commands {unquote(command_module), function_name, [then: then]}
end
end
def __command_proxy__({command_module, function_name, opts}) do
quote do
@doc """
#{unquote(command_module).__module_docs__()}
#{unquote(command_module).__field_docs__()}
"""
def unquote(function_name)(attrs \\ [], opts \\ []) do
opts = Keyword.merge(unquote(opts), opts)
BoundedContext.__dispatch_command__(unquote(command_module), attrs, opts)
end
@doc """
#{unquote(command_module).__module_docs__()}
#{unquote(command_module).__field_docs__()}
"""
def unquote(:"#{function_name}!")(attrs \\ [], opts \\ []) do
opts = Keyword.merge(unquote(opts), opts)
BoundedContext.__dispatch_command__!(unquote(command_module), attrs, opts)
end
end
end
@doc """
Creates proxy functions to create and execute the give query.
## Functions created
When given `ListUsers`
* `list_users!/0`
* `list_users!/1`
* `list_users!/2`
* `list_users/0`
* `list_users/1`
* `list_users/2`
* `list_users_query!/0`
* `list_users_query!/1`
* `list_users_query!/2`
* `list_users_query/0`
* `list_users_query/1`
* `list_users_query/2`
"""
defmacro query(query_module, opts \\ []) do
quote location: :keep do
Guards.ensure_is_query!(unquote(query_module))
function_name = BoundedContext.__function_name__(unquote(query_module), unquote(opts))
@queries {unquote(query_module), function_name}
end
end
def __query_proxy__({query_module, function_name}) do
quote do
@doc """
#{unquote(query_module).__module_docs__()}
#{unquote(query_module).__filter_docs__()}
"""
def unquote(function_name)(filters \\ [], opts \\ []) do
BoundedContext.__execute_query__(unquote(query_module), filters, opts)
end
@doc """
#{unquote(query_module).__module_docs__()}
#{unquote(query_module).__filter_docs__()}
"""
def unquote(:"#{function_name}!")(filters \\ [], opts \\ []) do
BoundedContext.__execute_query__!(unquote(query_module), filters, opts)
end
query_name = unquote(query_module).__name__()
query_headline_modifier = if query_name =~ ~r/^[aeiou]/i, do: "an", else: "a"
@doc """
Creates #{query_headline_modifier} [#{query_name}](`#{unquote(query_module)}`) query without executing it.
#{unquote(query_module).__filter_docs__()}
"""
def unquote(:"#{function_name}_query")(filters \\ [], opts \\ []) do
BoundedContext.__create_query__(unquote(query_module), filters, opts)
end
@doc """
Creates #{query_headline_modifier} [#{query_name}](`#{unquote(query_module)}`) query without executing it.
#{unquote(query_module).__filter_docs__()}
"""
def unquote(:"#{function_name}_query!")(filters \\ [], opts \\ []) do
BoundedContext.__create_query__!(unquote(query_module), filters, opts)
end
end
end
def __function_name__(module, opts) do
[name | _] =
module
|> Module.split()
|> Enum.reverse()
default_function_name =
name
|> to_string
|> Macro.underscore()
|> String.to_atom()
Keyword.get(opts, :as, default_function_name)
end
def __dispatch_command__(module, attrs, opts) do
then = Keyword.get(opts, :then, &Function.identity/1)
attrs
|> module.new(opts)
|> module.dispatch(opts)
|> __handle_command_result__(then)
end
def __dispatch_command__!(module, attrs, opts) do
then = Keyword.get(opts, :then, &Function.identity/1)
attrs
|> module.new!(opts)
|> module.dispatch(opts)
|> __handle_command_result__(then)
end
def __handle_command_result__(result, fun) when is_function(fun, 1), do: fun.(result)
def __handle_command_result__(_result, _other), do: raise("'then' should be a function/1")
def __create_query__(module, attrs, opts) do
module.new(attrs, opts)
end
def __create_query__!(module, attrs, opts) do
module.new!(attrs, opts)
end
def __execute_query__(module, attrs, opts) do
attrs
|> module.new(opts)
|> module.execute(opts)
end
def __execute_query__!(module, attrs, opts) do
attrs
|> module.new!(opts)
|> module.execute(opts)
end
end