Dependencies

Overview

With Dependencies, you can replace parts of Spree core with your custom code: Services and Workflows, CanCanCan Abilities (used for Permissions), and API Serializers (used for generating JSON API responses).

Replacing a whole class means keeping your copy in sync with every Spree release. If you only need to run code inside an existing flow — validating, reacting, or contributing data to a calculation — use a hook instead. Hooks survive upgrades.

Application (global) customization

This will change every aspect of the application (both APIs, Admin Panel, and Storefront). In your config/initializers/spree.rb file, you can set the following:

Spree.cart_update_service = MyStore::CartUpdate

or using the block syntax:

Spree.dependencies do |dependencies|
  dependencies.cart_update_service = MyStore::CartUpdate
end

Now let’s create your custom service.

mkdir -p app/services/my_store && touch app/services/my_store/cart_update.rb

And add the following code to it:

module MyStore
  class CartUpdate < Spree::Carts::Update
    def call(cart:, params:)
      result = super

      MyStore::ErpSync.push(result.value) if result.success?

      result
    end
  end
end

Inheriting and calling super keeps Spree’s behaviour and adds yours around it, which is usually what you want — a full rewrite means re-implementing logic that changes between releases.

Replacing a workflow

Workflow-backed seams end in _workflow (cart_add_item_workflow, carts_complete_workflow, payment_capture_workflow, …). A replacement subclasses the workflow and overrides perform:

module MyStore
  class AddItem < Spree::Carts::AddItem
    def perform(variant:, cart: nil, **rest)
      super

      # your logic, then the standard result
    end
  end
end

Spree.cart_add_item_workflow = MyStore::AddItem

Before writing this, check whether a hook covers your case — carts.add_item.validate and carts.add_item.after_item_added handle most reasons people replace this class, and they don’t need maintaining across upgrades.

Using dependencies in your code

When you need to use a dependency in your code, you can access it directly via the Spree module:

# Returns the resolved class (not a string)
Spree.cart_add_item_workflow.call(cart: cart, variant: variant, quantity: 1)

# For API dependencies, use the Spree.api accessor
Spree.api.storefront_cart_serializer.new(order).serializable_hash

Controller level customization

If you need to replace serializers or Services in a specific API endpoint you can create a code decorator:

mkdir -p app/controllers/spree && touch app/controllers/spree/cart_controller_decorator.rb

and add the following code to it:

module Spree
  module CartControllerDecorator
    def resource_serializer
      MyNewAwesomeCartSerializer
    end

    def add_item_service
      MyNewAwesomeAddItemToCart
    end
  end

  CartController.prepend(CartControllerDecorator)
end

This will change the serializer in this API endpoint to MyNewAwesomeCartSerializer and also it will swap the default add_item_service to MyNewAwesomeAddItemToCart. Different API endpoints can have different dependency injection points. You can review their source code to see what you can replace.

API level customization

Storefront API and Platform API have separate Dependencies injection points so you can easily customize one without touching the other. In your Spree initializer (config/initializers/spree.rb) please add:

Spree.api.storefront_cart_serializer = MyNewAwesomeCartSerializer
Spree.api.storefront_cart_add_item_service = MyNewAwesomeAddItemToCart

This will swap the default Cart serializer and Add Item to Cart service for your custom ones within all Storefront API endpoints that use those classes. You can mix and match both global and API-level customizations:

Spree.cart_add_item_workflow = MyNewAwesomeAddItemToCart
Spree.api.storefront_cart_add_item_service = AnotherAddItemToCart

The second line will have precedence over the first one, and the Storefront API will use AnotherAddItemToCart and the rest of the application will use MyNewAwesomeAddItemToCart.

Debugging dependencies

Spree provides rake tasks to help you debug and inspect dependencies:

List all dependencies

bin/rake spree:dependencies:list

This will output all dependencies with their current values:

[CORE]
cart_add_item_workflow          Spree::Carts::AddItem
carts_create_service            Spree::Carts::Create
cart_recalculate_workflow       Spree::Carts::Recalculate [OVERRIDDEN]
...

[API]
storefront_cart_serializer      Spree::V2::Storefront::CartSerializer
storefront_cart_add_item_service  MyApp::CartAddItem [OVERRIDDEN]
...

You can use grep to filter results:

bin/rake spree:dependencies:list | grep cart

Show only overridden dependencies

bin/rake spree:dependencies:overrides

This shows only the dependencies that have been customized, along with their original and current values:

[Core OVERRIDES]
cart_recalculate_workflow  Spree::Carts::Recalculate -> MyApp::CartRecalculate (config/initializers/spree.rb:15)

[API OVERRIDES]
storefront_cart_add_item_service  Spree::Carts::AddItem -> MyApp::CartAddItem (config/initializers/spree.rb:20)

Validate all dependencies

bin/rake spree:dependencies:validate

This validates that all dependencies can be resolved to valid classes. If any dependency points to a non-existent class, it will report an error:

..........F.........
1 invalid dependencies:
  [Core] cart_add_item_workflow: uninitialized constant NonExistentClass

Programmatic introspection

You can also inspect dependencies programmatically:

# Check all current values
Spree::Dependencies.current_values
# => [{name: :cart_add_item_workflow, current: MyApp::CartAddItem, default: 'Spree::Carts::AddItem', overridden: true}, ...]

# Check if a specific dependency is overridden
Spree::Dependencies.overridden?(:cart_add_item_workflow)
# => true

# Get override information (where it was set)
Spree::Dependencies.override_info(:cart_add_item_workflow)
# => {value: MyApp::CartAddItem, source: "config/initializers/spree.rb:15", set_at: 2024-01-15 10:30:00}

# Validate all dependencies resolve to valid classes
Spree::Dependencies.validate!
# => true (or raises Spree::DependencyError)

Renamed seams in Spree 6.0

Seams backed by a workflow were renamed from *_service to *_workflow in 6.0:

Legacy name	Current name
`cart_add_item_service`	`cart_add_item_workflow`
`cart_recalculate_service`	`cart_recalculate_workflow`
`carts_complete_service`	`carts_complete_workflow`
`cart_merge_strategy`	`cart_merge_workflow`
`order_cancel_service`	`order_cancel_workflow`
`order_complete_service`	`order_complete_workflow`
`fulfillment_create_service`	`fulfillment_create_workflow`
`payments_handle_webhook_service`	`payments_handle_webhook_workflow`

The legacy names stay readable for one release, but assigning to one no longer has any effect — the override is recorded and a deprecation warning names the seam to port to. A class written against the old service contract isn’t interchangeable with the workflow the new call sites use, so applying it silently would break checkout in ways that are hard to trace.If you override any of these, move to the *_workflow name and make sure your class subclasses the workflow. The legacy names are removed in Spree 6.1.

Backwards compatibility

The legacy string-based syntax is still supported for backwards compatibility:

# Legacy syntax (still works)
Spree::Dependencies.carts_create_service = 'MyStore::CartCreate'
result = Spree::Dependencies.carts_create_service.constantize

# New syntax (recommended)
Spree.carts_create_service = MyStore::CartCreate
result = Spree.carts_create_service

Both syntaxes can coexist, but the new syntax is recommended as it’s more concise and provides better error messages at assignment time.

Default values

Default values can be easily checked by:

Using the rake task: bin/rake spree:dependencies:list
Looking at the source code:
- Application (global) dependencies
- API level dependencies

Tutorial

Admin Panel

Customization Reference

Overview

Application (global) customization

Replacing a workflow

Using dependencies in your code

Controller level customization

API level customization

Debugging dependencies

List all dependencies

Show only overridden dependencies

Validate all dependencies

Programmatic introspection

Renamed seams in Spree 6.0

Backwards compatibility

Default values

​Overview

​Application (global) customization

​Replacing a workflow

​Using dependencies in your code

​Controller level customization

​API level customization

​Debugging dependencies

​List all dependencies

​Show only overridden dependencies

​Validate all dependencies

​Programmatic introspection

​Renamed seams in Spree 6.0

​Backwards compatibility

​Default values

Overview

Application (global) customization

Replacing a workflow

Using dependencies in your code

Controller level customization

API level customization

Debugging dependencies

List all dependencies

Show only overridden dependencies

Validate all dependencies

Programmatic introspection

Renamed seams in Spree 6.0

Backwards compatibility

Default values