Actions

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In Ash, actions are the primary way to interact with your resources. There are five types of actions:

All actions can be run in a transaction. Create, update and destroy actions are run in a transaction by default, whereas read and generic actions require opting in with transaction? true in the action definition. Each action has its own set of options, ways of calling it, and ways of customizing it. See the relevant guide for specifics on each action type. This topic focuses on idiomatic ways to use actions, and concepts that cross all action types.

Primary Actions

Primary actions are a way to inform the framework which actions should be used in certain "automated" circumstances, or in cases where an action has not been specified. If a primary action is attempted to be used but does not exist, you will get an error about it at runtime.

The place you typically need primary actions is when Managing Relationships. When using the defaults option to add default actions, they are marked as primary.

A simple example where a primary action would be used:

# No action is specified, so we look for a primary read.
Ash.get!(Resource, "8ba0ab56-c6e3-4ab0-9c9c-df70e9945281")

To mark an action as primary, add the option, i.e

read :action_name do
  primary? true
end

Accepting Inputs

Create and Update actions can accept attributes as input. There are two primary ways that you annotate this.

Using accept in specific actions

Each action can define what it accepts, for example:

create :create do
  accept [:name, :description]
end

You could then pass in %{name: "a name", description: "a description"} to this action.

Using default_accept for all actions

The resource can have a default_accept, declared in its actions block, which will be used as the accept list for create and update actions, if they don't define one.

actions do
  default_accept [:name, :description]

  create :create
  update :update

  update :special_update do
    accept [:something_else]
  end
end

In the example above, you can provide %{name: "a name", description: "a description"} to both the :create and :update actions, but only %{something_else: "some_value"} to :special_update.

Using module attributes for action specific accept lists

You can also use module attributes to define the accept list. This is useful if you have a lot of attributes and different variations for different actions.

@accepts_special_update [:name, :description, :foo, :bar, :baz]

@accepts_super_special_update @accepts_special_update ++ [:something_else, :another_thing]

actions do
  default_accept [:name, :description]

  create :create
  update :update

  update :special_update do
    accept @accepts_special_update
  end
end

This is extremely simple example

Context

There are two kinds of contexts in Ash:

  1. the context given to a changeset/action call, stored in changeset.context,
  2. the context given to a callback function like Ash.Resource.Change.change/3, which contains the above context in it's source_context key, as well as additional information specific to the callback, and/or commonly needed keys for callbacks (actor, tenant, etc.).

Actions accept a free-form map of context, which can be used for whatever you like. Whenever context is set, it is deep merged. I.e if you do changeset |> Ash.Changeset.set_context(%{a: %{b: 1}}) |> Ash.Changeset.set_context(%{a: %{c: 2}}), the resulting context will be %{a: %{b: 1, c: 2}}. Structs are not merged.

There are some special keys in context to note:

:private

The :private key is reserved for use by Ash itself. You shouldn't read from or write to it.

:shared

The :shared key will be passed to all nested actions built by Ash, and should be passed by you to any actions you call within changes/preparations etc. Whenever :shared context is set, it is also written to the outer context. For example set_context(%{shared: %{locale: "en"}}) is equivalent to set_context(%{shared: %{locale: "en"}, locale: "en"})

This will generally happen automatically if you use one of the two abstractions provided by Ash for threading options through to nested action calls.

Careful with shared

Shared context is passed to all nested actions, so don't pass massive values around, and also don't set context

:query_for

This is set on queries when they are being run for a "special" purpose. The values this can take are:

  • none, if a read action is being run, then no value is set for this context
  • :bulk_update, if the query is being built to power a bulk update action
  • :bulk_destroy, if the query is being built to power a bulk destroy action
  • :load, if the query is being built to power an Ash.load call

You can use this to adjust the behavior of your query preparations as needed.

:bulk_create, :bulk_update, :bulk_destroy

This is set on changesets when they are being run in bulk. The value will be a map with the following keys (more may be added in the future):

:index -> The index of the changeset in the bulk operation.

Ash.Scope.ToOpts

Ash.Scope.ToOpts is newer and is the recommended way to do this. In action callbacks in Ash, you will be provided with a context, which can be passed down as a scope option when running nested actions or building nested changesets/queries. For example:

def change(changeset, opts, context) do
  Ash.Changeset.after_action(changeset, fn changeset, result ->
    # automatically passes the `shared` context to the nested action
    MyApp.MyDomain.create_something_else(..., scope: context, other: :options)
  end)
end

To get the opts for a given scope, you can use Ash.Scope.to_opts(scope), but this is typically not necessary.

Ash.Context.to_opts/2

Ash.Context.to_opts/2 is a helper function that converts a context map into a list of options that can be passed to nested actions. It automatically passes the shared context to the nested action as well.

def change(changeset, opts, context) do
  Ash.Changeset.after_action(changeset, fn changeset, result ->
    # automatically passes the `shared` context to the nested action
    MyApp.MyDomain.create_something_else(..., Ash.Context.to_opts(context, other: :options))
  end)
end

Idiomatic Actions

Name Your Actions

The intent behind Ash is not to have you building simple CRUD style applications. In a typical set up you may have a resource with four basic actions, there is even a shorthand to accomplish this:

actions do
  defaults [:read, :destroy, create: :*, update: :*]
end

But that is just a simple way to get started, or to create resources that really don't do anything beyond those four operations. You can have as many actions as you want. The best designed Ash applications will have numerous actions, named after the intent behind how they are used. They won't have all reads going through a single read action, and the same goes for the other action types. The richer the actions on the resource, the better interface you can have. With that said, many resources may only have those four basic actions, especially those that are "managed" through some parent resource. See the guide on Managing Relationships for more.

Put everything inside the action

Ash provides utilities to modify queries and changesets outside of the actions on the resources. This is a very important tool in our tool belt, but it is very easy to abuse. The intent is that as much behavior as possible is put into the action. Here is the "wrong way" to do it. There is a lot going on here, so don't hesitate to check out other relevant guides if you see something you don't understand.

def top_tickets(user_id) do
  Ticket
  |> Ash.Query.for_read(:read)
  |> Ash.Query.filter(priority in [:medium, :high])
  |> Ash.Query.filter(representative_id == ^user_id)
  |> Ash.Query.filter(status == :open)
  |> Ash.Query.sort(opened_at: :desc)
  |> Ash.Query.limit(10)
  |> Helpdesk.Support.read!()
end

# in the resource

actions do
  defaults [:read, ...]
end

And here is the "right way", where the rules about getting the top tickets have been moved into the resource as a nicely named action, and included in the code_interface of that resource. The reality of the situation is that top_tickets/1 is meant to be obsoleted by your Ash resource! Here is how it should be done.

# in the resource

code_interface do
  define :top, args: [:user_id]
end

actions do
  read :top do
    argument :user_id, :uuid do
      allow_nil? false
    end

    prepare build(limit: 10, sort: [opened_at: :desc])

    filter expr(priority in [:medium, :high] and representative_id == ^arg(:user_id) and status == :open)
  end
end

Now, whatever code I had that would have called top_tickets/1 can now call Helpdesk.Support.Ticket.top(user.id). By doing it this way, you get the primary benefit of getting a nice simple interface to call into, but you also have a way to modify how the action is invoked in any way necessary, by going back to the old way of building the query manually. For example, if I also only want to see top tickets that were opened in the last 10 minutes:

Ticket
|> Ash.Query.for_read(:top, %{user_id: user.id})
|> Ash.Query.filter(opened_at > ago(10, :minute))
|> Helpdesk.Support.read!()

That is the best of both worlds! These same lessons transfer to changeset based actions as well.

Private Inputs

The concept of a "private input" can be somewhat paradoxical, but it can be used by actions that require something provided by the "system", as well as something provided by the caller. For example, you may want an ip_address input that can't be set by the user. For this, you have two options.

Private Options

create :create do
  argument :ip_address, :string, allow_nil?: false, public?: false

  ...
end
Ash.Changeset.for_create(Resource, :create, %{}, private_arguments: %{ip_address: "<ip_address>"})

Context

You can also provide things to the action via context. Context is a map that is a free form map provided to the action. Context is occasionally used by callers to provide additional information that the action may or may not use.

Context is deep merged with any existing context, and also contains a private key that is reserved for use by Ash internals. You should not remove or manipulate the private context key in any way.

create :create do
  ...
  change fn changeset, _ ->
    changeset.context # %{ip_address: "<ip_address>"}
  end
end
Ash.Changeset.for_create(Resource, :create, %{}, context: %{ip_address: "<ip_address>"})

Action Lifecycle

This section provides a comprehensive overview of the Ash resource action lifecycle, detailing when each phase executes in relation to database transactions.

Overview

Ash resource actions follow a well-defined lifecycle that ensures proper data validation, transformation, and persistence. The lifecycle is divided into three main phases:

  • Pre-Transaction Phase - Operations before database transaction
  • Transaction Phase - Operations within database transaction
  • Post-Transaction Phase - Operations after database transaction

Important Notes:

  • Query Actions: Read queries do not currently have before_transaction, after_transaction, or around_transaction callbacks
  • Around Action Behavior: around_action hooks do not complete their "end" phase if the action fails
  • Generic Actions: Generic actions are left out because they currently do not support hooks of any kind, or preparations/changes/validations.

Complete Lifecycle Flow

graph TD
    subgraph "Pre-Transaction Phase"
        START["Action Invocation<br/>(Ash.create, Ash.read, etc.)"] --> PREP["Changeset/Query Creation"]
        PREP --> AROUND_START["around_transaction (start)<br/>🚫 Not available for read/query actions"]
        AROUND_START --> BEFORE_TRANS["before_transaction<br/>🚫 Not available for read/query actions"]
    end
    
    subgraph "Transaction Phase"
        TRANS_START["🔒 Transaction Begins"] --> ACTION_PREP["Action Preparations/Validations/Changes<br/>(In order of definition)"]
        ACTION_PREP --> GLOBAL_PREP["Global Preparations/Validations/Changes<br/>(Resource-level, in order of definition)"]
        GLOBAL_PREP --> AROUND_ACTION_START["around_action (start)"]
        AROUND_ACTION_START --> BEFORE_ACTION["before_action"]
        BEFORE_ACTION --> DATA_LAYER["💾 Data Layer Operation<br/>(Database interaction)"]
        DATA_LAYER --> SUCCESS{"Success?"}
        SUCCESS -->|Yes| AFTER_ACTION["after_action<br/>(Success only)"]
        SUCCESS -->|No| ERROR_HANDLE["Error Handling"]
        AFTER_ACTION --> AROUND_ACTION_END["around_action (end)<br/>✅ Only on success"]
        ERROR_HANDLE --> TRANS_ROLLBACK["🔓 Transaction Rollback"]
        AROUND_ACTION_END --> TRANS_COMMIT["🔓 Transaction Commit"]
    end
    
    subgraph "Post-Transaction Phase"
        AFTER_TRANS["after_transaction<br/>(Always runs - success/error)<br/>🚫 Not available for read/query actions"] --> AROUND_END["around_transaction (end)<br/>🚫 Not available for read/query actions"]
        AROUND_END --> NOTIFICATIONS["Notifications<br/>(If enabled)"]
        NOTIFICATIONS --> RESULT["Return Result"]
    end
    
    %% Flow connections
    BEFORE_TRANS --> TRANS_START
    TRANS_COMMIT --> AFTER_TRANS
    TRANS_ROLLBACK --> AFTER_TRANS

Detailed Phase Breakdown

Pre-Transaction Phase (Outside Database Transaction)

1. Action Invocation
2. Changeset/Query Creation
  • Creates appropriate changeset or query structure
  • Applies initial transformations and validations
3. around_transaction (Start)
  • When: Before transaction begins
  • Purpose: Wrap entire transaction with setup/cleanup logic
  • Use Cases:
    • External service setup
    • Resource allocation
    • Logging/monitoring setup
  • Transaction Context: Outside transaction
  • Note: Not available for query/read actions
4. before_transaction
  • When: Just before transaction starts
  • Purpose: Operations that must happen before database transaction
  • Use Cases:
    • External API calls
    • File system operations
    • Cache warming
    • Non-transactional preparations
  • Transaction Context: Outside transaction
  • Note: Not available for query/read actions

Transaction Phase (Inside Database Transaction)

5. Transaction Begins 🔒
  • Database transaction is initiated
  • All subsequent operations until commit/rollback are atomic
6. Action Preparations/Validations/Changes
  • When: First operations inside transaction
  • Purpose: Execute action-specific preparations, validations, and changes
  • Order: Run in the order they are defined in the action (not grouped by type)
  • Operations:
    • Action-level preparations (query modifications, filters, sorts)
    • Action-level validations (business rules, constraints)
    • Action-level changes (data transformations, attribute modifications)
  • Transaction Context: Inside transaction
7. Global Preparations/Validations/Changes
  • When: After action-level operations, before action hooks
  • Purpose: Execute resource-level preparations, validations, and changes
  • Order: Run in the order they are defined at the resource level (not grouped by type)
  • Operations:
    • Resource-level preparations
    • Resource-level validations
    • Resource-level changes
    • Global business logic
  • Transaction Context: Inside transaction
8. around_action (Start)
  • When: Just before data layer operation
  • Purpose: Wrap the actual database operation
  • Use Cases:
    • Performance monitoring
    • Debugging and development tools
    • Advanced error handling
    • Action timing
  • Transaction Context: Inside transaction
  • Note: Must call the callback function
9. before_action
  • When: Immediately before data layer operation
  • Purpose: Final modifications before database interaction
  • Use Cases:
    • Last-minute data modifications
    • Transactional side effects
    • Audit logging
    • Final validations
  • Transaction Context: Inside transaction
10. Data Layer Operation 💾
  • When: Core of the transaction
  • Purpose: Actual database interaction
  • Operations:
    • INSERT, UPDATE, DELETE, SELECT operations
    • Constraint enforcement
    • Database-level validations
    • Index updates
  • Transaction Context: Inside transaction
11. Success/Error Decision Point
  • Determines if the operation succeeded or failed
  • Affects which subsequent hooks are called
12. after_action (Success Path Only)
  • When: After successful data layer operation
  • Purpose: Post-success operations within transaction
  • Use Cases:
    • Success-only side effects
    • Transactional cleanup
    • Related record updates
    • Success logging
  • Transaction Context: Inside transaction
  • Note: Only runs on successful operations
13. Error Handling (Error Path)
  • When: After failed data layer operation
  • Purpose: Handle errors within transaction context
  • Operations:
    • Error processing
    • Rollback preparation
    • Error logging
  • Transaction Context: Inside transaction
14. around_action (End)
  • When: After successful action completion only
  • Purpose: Cleanup and finalization within transaction
  • Use Cases:
    • Resource cleanup
    • Final transaction operations
    • Monitoring completion
  • Transaction Context: Inside transaction
  • Note: This phase does NOT execute if the action fails
15. Transaction Commits/Rollbacks 🔓
  • Success: Transaction commits, changes are persisted
  • Error: Transaction rolls back, changes are discarded
  • End of transactional context

Post-Transaction Phase (Outside Database Transaction)

16. after_transaction
  • When: After transaction completion (success or error)
  • Purpose: Operations that should happen regardless of outcome
  • Use Cases:
    • External service notifications
    • Cache invalidation
    • Cleanup operations
    • Logging (success and error cases)
    • Retry mechanisms - can change error results to success
  • Transaction Context: Outside transaction
  • Special Capability: Can transform the final result (e.g., retry failed operations)
  • Note: Always runs, regardless of success/failure (not available for query/read actions)
17. around_transaction (End)
  • When: Final cleanup phase
  • Purpose: Complete the transaction wrapper
  • Use Cases:
    • Resource deallocation
    • Final cleanup
    • Monitoring completion
  • Transaction Context: Outside transaction
  • Note: Not available for query/read actions
18. Notifications
  • When: After all hooks complete
  • Purpose: Broadcast events and notifications
  • Operations:
    • PubSub notifications
    • Event broadcasting
    • External system integrations
    • Webhook calls
  • Transaction Context: Outside transaction
19. Return Result
  • Success: Returns data with metadata
  • Error: Returns error details and context

Hook Execution Order

The hooks execute in the following order (as of Ash 3.0+):

For Create/Update/Destroy Actions:

  1. around_transaction (start)
  2. before_transaction
  3. Transaction begins
  4. Action preparations/validations/changes (in order of definition)
  5. Global preparations/validations/changes (in order of definition)
  6. around_action (start)
  7. before_action
  8. Data layer operation
  9. after_action (success only) OR Error handling
  10. around_action (end) - Only on success
  11. Transaction commits/rollbacks
  12. after_transaction
  13. around_transaction (end)

For Read/Query Actions:

  1. Transaction begins (if applicable)
  2. Action preparations/validations/changes (in order of definition)
  3. Global preparations/validations/changes (in order of definition)
  4. around_action (start)
  5. before_action
  6. Data layer operation
  7. after_action (success only) OR Error handling
  8. around_action (end) - Only on success
  9. Transaction commits/rollbacks (if applicable)

Key Points

Transaction Boundaries

  • Outside Transaction: around_transaction, before_transaction, after_transaction (not available for read/query actions)
  • Inside Transaction: Action preparations/validations/changes, Global preparations/validations/changes, around_action, before_action, after_action

Error Handling

  • after_action only runs on successful operations
  • around_action (end) only runs on successful operations
  • after_transaction always runs (success and error) - not available for read/query actions
  • after_transaction can change the final result - can transform errors into successes (useful for retries)
  • Transaction rollback occurs automatically on errors

Execution Order Details

  • Preparations/Validations/Changes: Run in the order they are defined, NOT grouped by type
  • Action-level preparations/validations/changes run first (in definition order)
  • Then global (resource-level) preparations/validations/changes run (in definition order)
  • Hook Order Changes (Ash 3.0+): Before/after action hooks now run in the order they are added (not reverse order)
  • Restriction: after_transaction hooks cannot be added from within other lifecycle hooks

Performance Considerations

  • Operations inside the transaction should be fast and focused
  • Long-running operations should be in before_transaction or after_transaction
  • Database connections are held during the entire transaction phase

Action Type Differences

Create/Update/Destroy Actions

  • Have full lifecycle including all transaction hooks
  • Support before_transaction, after_transaction, around_transaction
  • Run in transactions by default, unless no hooks of any kind are added to the changeset.
  • Have complete error handling and rollback capabilities

Read/Query Actions

  • Do not support before_transaction, after_transaction, or around_transaction hooks
  • Only support before_action, after_action, and around_action hooks
  • Do not run in transactions by default
  • Focus on data retrieval and filtering

Best Practices

  • Use before_transaction for external API calls (create/update/destroy only)
  • Use before_action for final data modifications
  • Use after_action for transactional side effects
  • Use after_transaction for external notifications (create/update/destroy only)
  • Use after_transaction for retry mechanisms and result transformation
  • Keep transaction phase operations fast and focused
  • Handle errors appropriately at each phase
  • Remember that around_action cleanup won't run on failures

Example Implementation

defmodule MyApp.User do
  use Ash.Resource

  actions do
    create :create do
      accept [:name, :email]
      argument :retries, :integer, default: 3, allow_nil?: false
      
      change before_transaction(fn changeset, _context ->
        # External API call before transaction
        case ExternalService.validate_email(changeset.attributes.email) do
          :ok -> changeset
          {:error, reason} -> Ash.Changeset.add_error(changeset, reason)
        end
      end)
      
      change before_action(fn changeset, _context ->
        # Final modifications before database
        Ash.Changeset.change_attribute(changeset, :created_at, DateTime.utc_now())
      end)
      
      change after_action(fn changeset, result, _context ->
        # Success-only operations within transaction
        Logger.info("User created: #{result.id}")
        {:ok, result}
      end)
      
      change fn changeset, context ->
        # Retry mechanism using after_transaction
        if changeset.arguments[:retries] > 0 do
          Ash.Changeset.after_transaction(changeset, fn 
            changeset, {:ok, result} ->
              # Success case - send notification and return result
              NotificationService.send_welcome_email(result)
              {:ok, result}
            changeset, {:error, _error} ->
              # Error case - retry with decremented counter
              __MODULE__
              |> Ash.Changeset.for_create(
                changeset.action.name, 
                Map.put(changeset.params, :retries, changeset.arguments.retries - 1), 
                scope: context
              )
              |> Ash.create()
          end)
        else
          # No retries left - add final after_transaction for cleanup
          Ash.Changeset.after_transaction(changeset, fn changeset, result ->
            case result do
              {:ok, user} -> 
                NotificationService.send_welcome_email(user)
                result
              error -> 
                Logger.error("User creation failed after all retries")
                error
            end
          end)
        end
      end
    end
  end
end

Key Points from Example:

  • Retry Logic: The after_transaction hook can transform a failed result into a new attempt
  • Result Transformation: Failed operations can become successful ones through retries
  • Context Preservation: The retry maintains the original context and decrements the retry counter
  • Conditional Behavior: Different after_transaction hooks based on retry availability
  • Final Cleanup: Even after retries are exhausted, cleanup operations still occur

This lifecycle ensures data consistency, proper error handling, and allows for complex business logic while maintaining transactional integrity.