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4 KiB
Optimistic Locking
Mix.install([{:ash, "~> 3.0.0-rc"}], consolidate_protocols: false)
# Set to `:debug` if you want to see ETS logs
Logger.configure(level: :warning)
Steps to add optimistic locking to an Ash.Resource
- Add a
:version
attribute to your resource.- This will typically be an
:integer
- with a default of
1
- and
allow_nil?: false
- This will typically be an
- If you want optimistic locking to occur for specific actions:
- Add
change optimistic_lock(:version)
to those specific actions
- Add
- If you want optimistic locking to occur for all actions:
- Add a global
changes
block, if you do not have one - Add
change optimistic_lock(:version)
- Add a global
- If you want to apply optimistic locking to many but not all actions:
- Add a global
changes
block, if you do not have one - Add
change optimistic_lock(:version), where: action_is(:list, :of, :actions, ...)
- Add a global
Need more context?
See the documentation for Ash.Resource.Change.OptimisticLock
Define a resource with a version attribute
defmodule Address do
use Ash.Resource,
domain: Domain,
data_layer: Ash.DataLayer.Ets
attributes do
uuid_primary_key :id
attribute :version, :integer, allow_nil?: false, default: 1
attribute :state, :string, allow_nil?: false
attribute :county, :string, allow_nil?: false
end
actions do
defaults [:read, create: [:state, :county]]
update :update do
accept [:state, :county]
change optimistic_lock(:version)
end
end
# apply to all actions
# changes do
# change optimistic_lock(:version)
# end
# apply to a list of actions
# changes do
# change optimistic_lock(:version), where: action_is([:list, :of, :actions])
# end
end
defmodule Domain do
use Ash.Domain,
validate_config_inclusion?: false
resources do
resource Address do
define(:get_address, action: :read, get_by: [:id])
define(:create_address, action: :create, args: [:state, :county])
define(:update_address, action: :update)
end
end
end
{:module, Domain, <<70, 79, 82, 49, 0, 2, 14, ...>>,
[
Ash.Domain.Dsl.Resources.Resource,
Ash.Domain.Dsl.Resources.Options,
Ash.Domain.Dsl,
%{opts: [], entities: [...]},
Ash.Domain.Dsl,
Ash.Domain.Dsl.Resources.Options,
...
]}
Triggering a StaleRecord error
address = Domain.create_address!("FL", "Pinellas")
Domain.update_address!(address, %{state: "NC", county: "Guilford"})
# `address` still has a version of `1`, so our optimistic lock should catch it!
Domain.update_address(address, %{county: "Miami-Dade"})
{:error,
%Ash.Error.Invalid{
changeset: nil,
query: nil,
action_input: nil,
errors: [
%Ash.Error.Changes.StaleRecord{
resource: "Address",
filter: %{"version" => 1},
splode: Ash.Error,
bread_crumbs: [],
vars: [],
path: [],
stacktrace: #Splode.Stacktrace<>,
class: :invalid
}
],
splode: Ash.Error,
bread_crumbs: [],
vars: [],
path: [],
stacktrace: #Splode.Stacktrace<>,
class: :invalid
}}
Refetching a record to get the latest version
address = Domain.create_address!("FL", "Pinellas")
Domain.update_address!(address, %{state: "NC", county: "Guilford"})
case Domain.update_address(address, %{county: "Miami-Dade"}) do
{:error, %Ash.Error.Invalid{errors: [%Ash.Error.Changes.StaleRecord{}]}} ->
# In a liveview, you wouldn't just refetch and resubmit
# you would show the user an error and have them submit the form again
address = Domain.get_address!(address.id)
Domain.update_address!(address, %{county: "Miami-Dade"})
{:ok, domain} ->
domain
end
#Address<
__meta__: #Ecto.Schema.Metadata<:loaded>,
id: "9f5d247e-fc44-41d1-80b4-8553c63855bb",
version: 3,
state: "NC",
county: "Miami-Dade",
aggregates: %{},
calculations: %{},
...
>