Domain-Driven Design with RAP: Modeling Business Domains

┌─────────────────────────────────────────────────────────────┐
│                    ENTERPRISE                                │
│  ┌─────────────────────┐    ┌─────────────────────────────┐ │
│  │  SALES CONTEXT      │    │  LOGISTICS CONTEXT          │ │
│  │  ┌───────────────┐  │    │  ┌───────────────────────┐  │ │
│  │  │ Order (BO)    │  │    │  │ Shipment (BO)         │  │ │
│  │  │ Customer      │──┼────┼──│ DeliveryAddress       │  │ │
│  │  │ OrderItem     │  │    │  │ ShipmentItem          │  │ │
│  │  └───────────────┘  │    │  └───────────────────────┘  │ │
│  │  ┌───────────────┐  │    │  ┌───────────────────────┐  │ │
│  │  │ Product (ref) │◄─┼────┼──│ Inventory (BO)        │  │ │
│  │  └───────────────┘  │    │  │ StockLevel            │  │ │
│  └─────────────────────┘    │  └───────────────────────┘  │ │
│                              └─────────────────────────────┘ │
└─────────────────────────────────────────────────────────────┘

" ROOT ENTITY = Aggregate Root
@AbapCatalog.viewEnhancementCategory: [#NONE]
@AccessControl.authorizationCheck: #CHECK
@EndUserText.label: 'Order - Root Entity (Aggregate)'

define root view entity ZI_Order
  as select from zorder
  composition [0..*] of ZI_OrderItem as _Items
  association [0..1] to ZI_Customer as _Customer
    on $projection.CustomerId = _Customer.CustomerId
{
  key order_id       as OrderId,
      customer_id    as CustomerId,
      order_date     as OrderDate,
      @Semantics.amount.currencyCode: 'CurrencyCode'
      total_amount   as TotalAmount,
      @Semantics.currencyCode: true
      currency_code  as CurrencyCode,
      status         as Status,

      " Administrative fields
      @Semantics.user.createdBy: true
      created_by     as CreatedBy,
      @Semantics.systemDateTime.createdAt: true
      created_at     as CreatedAt,

      " Associations
      _Items,
      _Customer
}

" CHILD ENTITY - Part of the Order Aggregate
@AbapCatalog.viewEnhancementCategory: [#NONE]
@AccessControl.authorizationCheck: #CHECK
@EndUserText.label: 'Order Item - Child Entity'

define view entity ZI_OrderItem
  as select from zorder_item
  association to parent ZI_Order as _Order
    on $projection.OrderId = _Order.OrderId
  association [1..1] to ZI_Product as _Product
    on $projection.ProductId = _Product.ProductId
{
  key order_id       as OrderId,
  key item_id        as ItemId,
      product_id     as ProductId,
      quantity       as Quantity,
      @Semantics.amount.currencyCode: 'CurrencyCode'
      unit_price     as UnitPrice,
      @Semantics.currencyCode: true
      currency_code  as CurrencyCode,

      " Calculated field
      quantity * unit_price as LineTotal,

      _Order,
      _Product
}

" Value Object as CDS Structure
@EndUserText.label: 'Address Value Object'
define structure zs_address {
  street      : abap.char(60);
  house_number: abap.char(10);
  postal_code : abap.char(10);
  city        : abap.char(40);
  country     : land1;
}

" Usage in Entity
define root view entity ZI_Customer
  as select from zcustomer
{
  key customer_id    as CustomerId,
      customer_name  as CustomerName,

      " Value Object: Address
      street         as AddressStreet,
      house_number   as AddressHouseNumber,
      postal_code    as AddressPostalCode,
      city           as AddressCity,
      country        as AddressCountry
}

managed implementation in class zbp_i_order unique;
strict ( 2 );

define behavior for ZI_Order alias Order
persistent table zorder
lock master
authorization master ( instance )
etag master LastChangedAt
{
  create;
  update;
  delete;

  " Items are created/changed through Order
  association _Items { create; }

  " Ensure aggregate invariants
  validation validateOrderConsistency on save { create; update; }

  " Domain Events
  event OrderCreated;
  event OrderConfirmed;
}

define behavior for ZI_OrderItem alias OrderItem
persistent table zorder_item
lock dependent by _Order
authorization dependent by _Order
{
  update;
  delete;

  " No direct creation - only through Order
  field ( readonly ) OrderId;

  association _Order;
}

CLASS lhc_order DEFINITION INHERITING FROM cl_abap_behavior_handler.
  PRIVATE SECTION.
    METHODS validateOrderConsistency FOR VALIDATE ON SAVE
      IMPORTING keys FOR Order~validateOrderConsistency.
ENDCLASS.

CLASS lhc_order IMPLEMENTATION.
  METHOD validateOrderConsistency.
    " Check aggregate invariants
    READ ENTITIES OF zi_order IN LOCAL MODE
      ENTITY Order
      ALL FIELDS WITH CORRESPONDING #( keys )
      RESULT DATA(lt_orders).

    " Load items
    READ ENTITIES OF zi_order IN LOCAL MODE
      ENTITY Order BY \_Items
      ALL FIELDS WITH CORRESPONDING #( keys )
      RESULT DATA(lt_items).

    LOOP AT lt_orders INTO DATA(ls_order).
      " Invariant 1: At least one item required
      DATA(lt_order_items) = FILTER #( lt_items
        WHERE OrderId = ls_order-OrderId ).

      IF lines( lt_order_items ) = 0.
        APPEND VALUE #(
          %tky = ls_order-%tky
          %msg = new_message_with_text(
            severity = if_abap_behv_message=>severity-error
            text     = 'Order must contain at least one item'
          )
        ) TO reported-order.
        APPEND VALUE #( %tky = ls_order-%tky ) TO failed-order.
        CONTINUE.
      ENDIF.

      " Invariant 2: Total amount must match items
      DATA(lv_calculated_total) = REDUCE decfloat34(
        INIT sum = CONV decfloat34( 0 )
        FOR item IN lt_order_items
        NEXT sum = sum + ( item-Quantity * item-UnitPrice )
      ).

      IF ls_order-TotalAmount <> lv_calculated_total.
        APPEND VALUE #(
          %tky = ls_order-%tky
          %element-TotalAmount = if_abap_behv=>mk-on
          %msg = new_message_with_text(
            severity = if_abap_behv_message=>severity-error
            text     = 'Total amount does not match items'
          )
        ) TO reported-order.
        APPEND VALUE #( %tky = ls_order-%tky ) TO failed-order.
      ENDIF.
    ENDLOOP.
  ENDMETHOD.
ENDCLASS.

METHOD create_order_with_items.
  " Deep Insert - Create aggregate as a whole
  MODIFY ENTITIES OF zi_order
    ENTITY Order
    CREATE FIELDS ( CustomerId OrderDate TotalAmount CurrencyCode Status )
    WITH VALUE #( (
      %cid       = 'ORDER_1'
      CustomerId = iv_customer_id
      OrderDate  = cl_abap_context_info=>get_system_date( )
      TotalAmount = lv_total
      CurrencyCode = 'EUR'
      Status     = 'NEW'
    ) )

    CREATE BY \_Items
    FIELDS ( ProductId Quantity UnitPrice CurrencyCode )
    WITH VALUE #(
      ( %cid_ref = 'ORDER_1'
        %target  = VALUE #(
          ( %cid       = 'ITEM_1'
            ProductId  = 'PROD001'
            Quantity   = 2
            UnitPrice  = '100.00'
            CurrencyCode = 'EUR' )
          ( %cid       = 'ITEM_2'
            ProductId  = 'PROD002'
            Quantity   = 1
            UnitPrice  = '250.00'
            CurrencyCode = 'EUR' )
        )
      )
    )
    MAPPED DATA(lt_mapped)
    FAILED DATA(lt_failed)
    REPORTED DATA(lt_reported).

  " All or nothing - transactional
  IF lt_failed IS NOT INITIAL.
    " Rollback automatic through RAP Runtime
    RAISE EXCEPTION TYPE cx_order_creation_failed.
  ENDIF.

  COMMIT ENTITIES.
ENDMETHOD.

" Interface for Domain Service
INTERFACE zif_pricing_service.
  METHODS calculate_order_total
    IMPORTING
      it_items         TYPE ztt_order_items
      iv_customer_tier TYPE zdd_customer_tier
    RETURNING
      VALUE(rs_result) TYPE zs_pricing_result.

  METHODS apply_discount
    IMPORTING
      iv_subtotal      TYPE decfloat34
      iv_discount_code TYPE zdd_discount_code
    RETURNING
      VALUE(rv_total)  TYPE decfloat34.
ENDINTERFACE.

" Implementation
CLASS zcl_pricing_service DEFINITION
  PUBLIC FINAL CREATE PUBLIC.

  PUBLIC SECTION.
    INTERFACES zif_pricing_service.

  PRIVATE SECTION.
    METHODS get_customer_discount
      IMPORTING iv_tier TYPE zdd_customer_tier
      RETURNING VALUE(rv_discount) TYPE decfloat34.
ENDCLASS.

CLASS zcl_pricing_service IMPLEMENTATION.
  METHOD zif_pricing_service~calculate_order_total.
    " Calculate subtotal
    DATA(lv_subtotal) = REDUCE decfloat34(
      INIT sum = CONV decfloat34( 0 )
      FOR item IN it_items
      NEXT sum = sum + ( item-quantity * item-unit_price )
    ).

    " Apply customer discount
    DATA(lv_discount) = get_customer_discount( iv_customer_tier ).
    DATA(lv_discount_amount) = lv_subtotal * lv_discount / 100.

    rs_result-subtotal = lv_subtotal.
    rs_result-discount_percentage = lv_discount.
    rs_result-discount_amount = lv_discount_amount.
    rs_result-total = lv_subtotal - lv_discount_amount.
  ENDMETHOD.

  METHOD zif_pricing_service~apply_discount.
    " Validate and apply discount code
    SELECT SINGLE discount_percentage
      FROM zdiscount_codes
      WHERE code = @iv_discount_code
        AND valid_from <= @cl_abap_context_info=>get_system_date( )
        AND valid_to >= @cl_abap_context_info=>get_system_date( )
      INTO @DATA(lv_percentage).

    IF sy-subrc = 0.
      rv_total = iv_subtotal * ( 1 - lv_percentage / 100 ).
    ELSE.
      rv_total = iv_subtotal.
    ENDIF.
  ENDMETHOD.

  METHOD get_customer_discount.
    CASE iv_tier.
      WHEN 'GOLD'.
        rv_discount = 15.
      WHEN 'SILVER'.
        rv_discount = 10.
      WHEN 'BRONZE'.
        rv_discount = 5.
      WHEN OTHERS.
        rv_discount = 0.
    ENDCASE.
  ENDMETHOD.
ENDCLASS.

CLASS lhc_order DEFINITION INHERITING FROM cl_abap_behavior_handler.
  PRIVATE SECTION.
    METHODS recalculateTotal FOR MODIFY
      IMPORTING keys FOR ACTION Order~recalculateTotal
      RESULT result.
ENDCLASS.

CLASS lhc_order IMPLEMENTATION.
  METHOD recalculateTotal.
    " Load Order and Items
    READ ENTITIES OF zi_order IN LOCAL MODE
      ENTITY Order
      ALL FIELDS WITH CORRESPONDING #( keys )
      RESULT DATA(lt_orders).

    READ ENTITIES OF zi_order IN LOCAL MODE
      ENTITY Order BY \_Items
      ALL FIELDS WITH CORRESPONDING #( keys )
      RESULT DATA(lt_items).

    READ ENTITIES OF zi_order IN LOCAL MODE
      ENTITY Order BY \_Customer
      FIELDS ( CustomerTier )
      WITH CORRESPONDING #( keys )
      RESULT DATA(lt_customers).

    " Instantiate Domain Service
    DATA(lo_pricing) = NEW zcl_pricing_service( ).

    LOOP AT lt_orders INTO DATA(ls_order).
      " Get items and customer data
      DATA(lt_order_items) = FILTER #( lt_items
        WHERE OrderId = ls_order-OrderId ).
      DATA(ls_customer) = VALUE #( lt_customers[
        CustomerId = ls_order-CustomerId ] OPTIONAL ).

      " Call Domain Service
      DATA(ls_pricing) = lo_pricing->zif_pricing_service~calculate_order_total(
        it_items         = CORRESPONDING #( lt_order_items )
        iv_customer_tier = ls_customer-CustomerTier ).

      " Update Aggregate
      MODIFY ENTITIES OF zi_order IN LOCAL MODE
        ENTITY Order
        UPDATE FIELDS ( TotalAmount DiscountAmount )
        WITH VALUE #( (
          %tky           = ls_order-%tky
          TotalAmount    = ls_pricing-total
          DiscountAmount = ls_pricing-discount_amount
        ) ).
    ENDLOOP.

    " Return result
    READ ENTITIES OF zi_order IN LOCAL MODE
      ENTITY Order
      ALL FIELDS WITH CORRESPONDING #( keys )
      RESULT result.
  ENDMETHOD.
ENDCLASS.

" Behavior Definition with Events
managed implementation in class zbp_i_order unique;

define behavior for ZI_Order alias Order
{
  " ... Standard operations ...

  " Declare Domain Events
  event OrderCreated parameter zs_order_created_event;
  event OrderConfirmed parameter zs_order_confirmed_event;
  event OrderShipped parameter zs_order_shipped_event;
  event OrderCancelled;
}

" Event Payload Definition
@EndUserText.label: 'Order Created Event'
define abstract entity ZA_OrderCreatedEvent
{
  OrderId      : abap.numc(10);
  CustomerId   : abap.numc(10);
  OrderDate    : abap.dats;
  TotalAmount  : abap.dec(15,2);
  CurrencyCode : abap.cuky;
  ItemCount    : abap.int4;
}

CLASS lhc_order IMPLEMENTATION.
  METHOD confirmOrder.
    " Change status
    MODIFY ENTITIES OF zi_order IN LOCAL MODE
      ENTITY Order
      UPDATE FIELDS ( Status ConfirmedAt )
      WITH VALUE #( FOR key IN keys
        ( %tky        = key-%tky
          Status      = 'CONFIRMED'
          ConfirmedAt = utclong_current( ) ) )
      FAILED failed
      REPORTED reported.

    " Read current data
    READ ENTITIES OF zi_order IN LOCAL MODE
      ENTITY Order
      ALL FIELDS WITH CORRESPONDING #( keys )
      RESULT DATA(lt_orders).

    " Raise Domain Event
    LOOP AT lt_orders INTO DATA(ls_order).
      RAISE ENTITY EVENT zi_order~OrderConfirmed
        FROM VALUE #( (
          %key       = ls_order-%key
          %param     = VALUE zs_order_confirmed_event(
            order_id       = ls_order-OrderId
            customer_id    = ls_order-CustomerId
            confirmed_at   = ls_order-ConfirmedAt
            total_amount   = ls_order-TotalAmount
            currency_code  = ls_order-CurrencyCode
          )
        ) ).
    ENDLOOP.

    " Result
    result = CORRESPONDING #( lt_orders ).
  ENDMETHOD.
ENDCLASS.

CLASS zcl_logistics_event_handler DEFINITION
  PUBLIC FINAL CREATE PUBLIC.

  PUBLIC SECTION.
    INTERFACES if_rap_event_handler.
ENDCLASS.

CLASS zcl_logistics_event_handler IMPLEMENTATION.
  METHOD if_rap_event_handler~handle_event.
    CASE iv_event_name.
      WHEN 'ORDERCONFIRMED'.
        " Read event data
        DATA ls_event TYPE zs_order_confirmed_event.
        ls_event = CORRESPONDING #( is_event_data ).

        " Create Shipment in Logistics Context
        MODIFY ENTITIES OF zi_shipment
          ENTITY Shipment
          CREATE FIELDS ( OrderId CustomerId Status )
          WITH VALUE #( (
            %cid       = 'SHIP_1'
            OrderId    = ls_event-order_id
            CustomerId = ls_event-customer_id
            Status     = 'PENDING'
          ) )
          MAPPED DATA(lt_mapped)
          FAILED DATA(lt_failed)
          REPORTED DATA(lt_reported).

        IF lt_failed IS INITIAL.
          COMMIT ENTITIES.
        ENDIF.
    ENDCASE.
  ENDMETHOD.
ENDCLASS.

" Entity names correspond to business terms
define root view entity ZI_SalesOrder      " Sales Order
define view entity ZI_SalesOrderItem       " Sales Order Item
define view entity ZI_DeliveryNote         " Delivery Note
define view entity ZI_Invoice              " Invoice
define root view entity ZI_Customer        " Customer

" Field names are self-explanatory
@EndUserText.label: 'Sales Order'
define root view entity ZI_SalesOrder
{
  key order_number        as OrderNumber,        " Order Number
      customer_number     as CustomerNumber,     " Customer Number
      order_date          as OrderDate,          " Order Date
      requested_delivery  as RequestedDelivery,  " Requested Delivery Date
      net_value           as NetValue,           " Net Value
      tax_amount          as TaxAmount,          " Tax Amount
      gross_value         as GrossValue,         " Gross Value
      payment_terms       as PaymentTerms,       " Payment Terms
      shipping_method     as ShippingMethod,     " Shipping Method
      order_status        as OrderStatus         " Order Status
}

" Custom data elements for business terms
@EndUserText.label: 'Order Number'
@AbapCatalog.dataMaintenance: #ALLOWED
define type zdd_order_number : abap.numc(10);

@EndUserText.label: 'Customer Number'
define type zdd_customer_number : abap.numc(10);

@EndUserText.label: 'Order Status'
define type zdd_order_status : abap.char(2);

" Usage in table and CDS
define table zsales_order {
  key client       : abap.clnt not null;
  key order_number : zdd_order_number not null;
  customer_number  : zdd_customer_number;
  order_status     : zdd_order_status;
}

" Interface to external system
INTERFACE zif_external_product_service.
  METHODS get_product
    IMPORTING iv_external_id TYPE string
    RETURNING VALUE(rs_product) TYPE zs_external_product.
ENDINTERFACE.

" Anti-Corruption Layer
CLASS zcl_product_acl DEFINITION
  PUBLIC FINAL CREATE PUBLIC.

  PUBLIC SECTION.
    METHODS constructor
      IMPORTING io_external_service TYPE REF TO zif_external_product_service.

    METHODS get_product_for_order
      IMPORTING iv_product_id TYPE zdd_product_id
      RETURNING VALUE(rs_product) TYPE zs_order_product
      RAISING cx_product_not_found.

  PRIVATE SECTION.
    DATA mo_external_service TYPE REF TO zif_external_product_service.

    METHODS translate_product
      IMPORTING is_external TYPE zs_external_product
      RETURNING VALUE(rs_internal) TYPE zs_order_product.
ENDCLASS.

CLASS zcl_product_acl IMPLEMENTATION.
  METHOD constructor.
    mo_external_service = io_external_service.
  ENDMETHOD.

  METHOD get_product_for_order.
    " Fetch external product
    DATA(ls_external) = mo_external_service->get_product(
      CONV #( iv_product_id ) ).

    IF ls_external IS INITIAL.
      RAISE EXCEPTION TYPE cx_product_not_found.
    ENDIF.

    " Translate to own domain model
    rs_product = translate_product( ls_external ).
  ENDMETHOD.

  METHOD translate_product.
    " Map to own structure
    rs_internal-product_id = is_external-sku.
    rs_internal-name = is_external-title.
    rs_internal-price = is_external-list_price.
    rs_internal-currency = is_external-currency_iso.

    " Map external categories to internal
    CASE is_external-category_code.
      WHEN 'ELEC'.
        rs_internal-product_group = 'ELECTRONICS'.
      WHEN 'FURN'.
        rs_internal-product_group = 'FURNITURE'.
      WHEN OTHERS.
        rs_internal-product_group = 'OTHER'.
    ENDCASE.
  ENDMETHOD.
ENDCLASS.

┌─────────────────────────────────────────────────────────────────┐
│                       CONTEXT MAP                                │
├─────────────────────────────────────────────────────────────────┤
│                                                                  │
│   ┌──────────────┐         Events          ┌──────────────────┐ │
│   │    SALES     │ ──────────────────────► │    LOGISTICS     │ │
│   │   Context    │   OrderConfirmed        │     Context      │ │
│   │              │   OrderCancelled        │                  │ │
│   │  [Upstream]  │                         │   [Downstream]   │ │
│   └──────────────┘                         └──────────────────┘ │
│          │                                          │           │
│          │ API Call                                 │           │
│          ▼                                          │           │
│   ┌──────────────┐                                  │           │
│   │   PRODUCT    │ ◄────────────────────────────────┘           │
│   │   Context    │        ACL (Read-Only)                       │
│   │              │                                              │
│   │  [Upstream]  │                                              │
│   └──────────────┘                                              │
│          │                                                       │
│          │ Conformist                                            │
│          ▼                                                       │
│   ┌──────────────┐                                              │
│   │   EXTERNAL   │                                              │
│   │   Catalog    │                                              │
│   │   (SAP S/4)  │                                              │
│   └──────────────┘                                              │
└─────────────────────────────────────────────────────────────────┘

" GOOD: Order is Aggregate Root with Items as Children
define root view entity ZI_Order
  composition [0..*] of ZI_OrderItem as _Items  " Part of the Aggregate

" BAD: Aggregate too large
define root view entity ZI_Order
  composition [0..*] of ZI_OrderItem as _Items
  composition [0..*] of ZI_Invoice as _Invoices     " Own Aggregate!
  composition [0..*] of ZI_Shipment as _Shipments   " Own Aggregate!

" Determination updates derived values in the Aggregate
determination calculateTotals on modify {
  field Quantity, UnitPrice;  " On item changes
}

METHOD calculateTotals.
  " Sum all items
  DATA(lv_total) = REDUCE decfloat34(
    INIT sum = CONV decfloat34( 0 )
    FOR item IN lt_items
    NEXT sum = sum + item-LineTotal
  ).

  " Update Root Entity
  MODIFY ENTITIES OF zi_order IN LOCAL MODE
    ENTITY Order
    UPDATE FIELDS ( TotalAmount )
    WITH VALUE #( ( %tky = ls_order-%tky
                    TotalAmount = lv_total ) ).
ENDMETHOD.

" Repository Interface for Aggregate
INTERFACE zif_order_repository.
  METHODS find_by_id
    IMPORTING iv_order_id TYPE zdd_order_id
    RETURNING VALUE(rs_order) TYPE zs_order_aggregate
    RAISING cx_not_found.

  METHODS find_by_customer
    IMPORTING iv_customer_id TYPE zdd_customer_id
    RETURNING VALUE(rt_orders) TYPE ztt_order_aggregates.

  METHODS save
    IMPORTING is_order TYPE zs_order_aggregate
    RAISING cx_save_failed.
ENDINTERFACE.

" RAP-based Implementation
CLASS zcl_order_repository DEFINITION
  PUBLIC FINAL CREATE PUBLIC.

  PUBLIC SECTION.
    INTERFACES zif_order_repository.
ENDCLASS.

CLASS zcl_order_repository IMPLEMENTATION.
  METHOD zif_order_repository~find_by_id.
    READ ENTITIES OF zi_order
      ENTITY Order
      ALL FIELDS WITH VALUE #( ( OrderId = iv_order_id ) )
      RESULT DATA(lt_orders)
      FAILED DATA(lt_failed).

    IF lt_failed IS NOT INITIAL OR lt_orders IS INITIAL.
      RAISE EXCEPTION TYPE cx_not_found.
    ENDIF.

    " Load items
    READ ENTITIES OF zi_order
      ENTITY Order BY \_Items
      ALL FIELDS WITH VALUE #( ( OrderId = iv_order_id ) )
      RESULT DATA(lt_items).

    " Assemble Aggregate
    rs_order-header = CORRESPONDING #( lt_orders[ 1 ] ).
    rs_order-items = CORRESPONDING #( lt_items ).
  ENDMETHOD.
ENDCLASS.

" GOOD: Business Action
action confirmOrder result [1] $self;
action shipOrder parameter ZA_ShipmentDetails result [1] $self;
action cancelOrder parameter ZA_CancellationReason result [1] $self;

" BAD: Technical Action
action setStatusConfirmed result [1] $self;
action updateShippingData parameter ZA_ShippingData result [1] $self;