BTP & Integrationintermediate

BTP CAP Part 5: Domain Modeling with Entities, Associations, Compositions and Aspects

Key takeaway

Model the domain well in CDS: entities with keys (cuid), reusable aspects (managed, temporal), types and code lists, associations (references) vs compositions (contained children with deep insert/delete), and modeling patterns that keep services and UIs simple.

Explanation

📌 KEY POINTS
✅ Use aspects from @sap/cds/common: cuid (UUID key), managed (created/modified fields), Currency, Country, CodeList.
✅ Associations reference independent entities (e.g. Order → Customer).
✅ Compositions model contained children (e.g. Order → Items) with deep insert, update and cascade delete.
✅ Keep the domain model independent of any single UI or consumer.
⚠️ Modeling independent entities (like Address shared by many) as compositions causes unexpected cascade deletes.

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▶ WHERE WE ARE
Part 4 covered SaaS. Now the model itself.

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▶ 1. ENTITIES & KEYS

cuid, natural keys where needed.

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▶ 2. ASPECTS

managed, temporal, custom aspects.

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▶ 3. ASSOCIATIONS

To-one, to-many with backlink (on).

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▶ 4. COMPOSITIONS

Contained children; deep operations.

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▶ 5. PATTERNS

Code lists, localized texts, reuse.

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▶ STEP BY STEP

Model Orders with composition of Items.
Associate Orders to Customers.
Test deep insert via OData.

✅ CHECKPOINT: deleting an order deletes its items but not the customer.

Code example

ABAP Code

===== db/schema.cds =====using { cuid, managed, Currency, sap.common.CodeList } from '@sap/cds/common';entity Orders : cuid, managed {  customer : Association to Customers;  items    : Composition of many OrderItems on items.parent = $self;  currency : Currency;  status   : Association to OrderStatus;}entity OrderItems : cuid { parent : Association to Orders; product : String; qty : Integer; }entity Customers : cuid { name : String; }entity OrderStatus : CodeList { key code : String(1); }

Real project scenario

An application modeled Address as a composition of Customer and of Order; deleting an order deleted addresses still used by customers. Remodeling Address as an associated entity fixed the data loss.

Common mistakes

Compositions for shared entities.
No aspects.
UI-driven modeling.
Late renames.
Missing backlinks.

Best practices

Composition only for contained data.
Use common aspects.
Consumer-independent model.
Stable names.
Proper on-conditions.

Interview angle

Questions: "Association vs composition?", "What are aspects?", "What is deep insert?"
Strong answer: keys/aspects, associations, compositions, patterns, lifecycle implications.

Practice this lesson

Quick check

1. What is the key distinguishing behavior of a 'composition' relationship compared to an 'association' in a CDS data model?

2. Deleting an order also deleted addresses still used by customers. What modeling error caused this?

3. Which aspect from @sap/cds/common adds created/modified timestamps and users?

Interview questions

1. An order-management CAP model causes accidental data loss and complex services. How do you improve the domain model?

Answer it in your own words first, then compare.

2. What are the most important design decisions, trade-offs, and best practices in CAP?