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A collection of handy Elixir macros for CQRS applications.
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lib/cqrs/domain_event.ex
defmodule Cqrs.DomainEvent do
@moduledoc """
Defines a new domain event struct
## Options
* `:from` _optional_ - a struct to derive fields from.
* `:with` _optional_ - a list of `atom` field names to add.
* `:drop` _optional_ - a list of `atom` field names to remove from any field derived
from the struct in the `:from` option.
* `:version` _optional_ - a version value. Defaults to `1`
## Example
defmodule DeleteUser do
use Cqrs.Command
field :id, :integer
def handle_dispatch(command, _opts) do
{:ok, :no_impl}
end
end
defmodule UserDeleted do
use Cqrs.DomainEvent,
from: DeleteUser,
with: [:from],
version: 2
end
iex> cmd = DeleteUser.new!(id: 668)
...> event = UserDeleted.new(cmd, from: "chris")
...> %{id: event.id, from: event.from, version: event.version}
%{id: 668, from: "chris", version: 2}
"""
alias Cqrs.{DomainEvent, Guards}
defmacro __using__(opts) do
quote generated: true, location: :keep do
version = Keyword.get(unquote(opts), :version, 1)
inherited_keys = DomainEvent.inherit_keys(unquote(opts))
explicit_keys = Keyword.get(unquote(opts), :with, []) |> List.wrap()
keys_to_drop = Keyword.get(unquote(opts), :drop, []) |> List.wrap()
if Code.ensure_loaded?(Jason), do: @derive(Jason.Encoder)
defstruct (inherited_keys ++ explicit_keys)
|> Enum.reject(&Enum.member?(keys_to_drop, &1))
|> List.delete(:created_at)
|> Kernel.++([:created_at, {:version, version}])
def new(source \\ [], attrs \\ []) do
DomainEvent.new(__MODULE__, source, attrs)
end
end
end
@doc false
def inherit_keys(opts) do
case Keyword.get(opts, :from) do
nil ->
[]
source when is_atom(source) ->
Guards.ensure_is_struct!(source)
Map.keys(source.__struct__())
source ->
"#{source} should be a valid struct to use with DomainEvent"
end
end
@doc false
def new(module, source, attrs) when is_atom(module) do
fields =
source
|> normalize()
|> Map.merge(normalize(attrs))
|> Map.put(:created_at, DateTime.utc_now())
struct(module, fields)
end
defp normalize(values) when is_struct(values), do: Map.from_struct(values)
defp normalize(values) when is_map(values), do: values
defp normalize(values) when is_list(values), do: Enum.into(values, %{})
end