Types of Association in CDS ?

DPM125 — Tue, 05 Aug 2025 18:50:30 +0000

Exposed Associations

An exposed association is one that is defined in a CDS view and is made available (exposed) to consumers of the view — such as other CDS views, analytical queries, or OData services. You define the association using the association […] to clause and then expose it using an alias (typically starting with an underscore _) in the SELECT list.

define view ZI_SalesOrder as select from ZSalesOrderHeader
{
    key SalesOrderID,
    CustomerID,

    association [0..1] to ZI_Customer as _Customer 
        on _Customer.CustomerID = ZSalesOrderHeader.CustomerID

    // Exposing the association
    _Customer
}

Key Points:

You can reuse exposed associations in other views.
Useful in modular CDS design.
Can be traversed via path expressions (e.g., _Customer.Name).

Ad-hoc Associations

Ad-hoc associations are associations that are used inline (on-the-fly) via path expressions, without needing to expose the association explicitly in the SELECT list. If an association (like _Customer) is already defined in a view (exposed or implicit), you can use it ad-hoc in the SELECT or WHERE clause without re-exposing it.

define view ZI_SalesOrder as select from ZSalesOrderHeader
{
    key SalesOrderID,
    _Customer.Name    // Ad-hoc usage of the association
}

Key Points:

No need to expose _Customer again in the select list.
You’re just traversing the association to access fields of the target entity.
Makes CDS views more compact and readable.

What is the difference between association vs Joins in CDS ?

DPM125 — Tue, 05 Aug 2025 18:30:22 +0000

Association An association is a declarative relationship between CDS entities (like foreign keys), defined using the association keyword. Key Characteristics: Lazy/Evaluated-on-demand: Data from the association is not fetched unless it is explicitly accessed using a path expression (like to_customer.name). Navigation-style access: You can access associated data using dot (.) notation. Defined once, reused many times: Associations can be defined once and used in multiple views or queries. Cardinality can be defined: e.g. [0..1], [1..*].

define view ZSalesOrder as select from sales_order
association [0..1] to customer as _Customer on $projection.customer_id = _Customer.id
{
key sales_order_id,
customer_id,
_Customer.name
}

Here, _Customer is an association. It won’t trigger a join unless _Customer.name is accessed.

Join

A join is an explicit operation in CDS to combine two data sources based on a condition, much like in SQL. Key Characteristics: Eager execution: The join happens immediately during view evaluation. More control: You control the type of join (INNER, LEFT OUTER, etc.). Typically used when data from both tables is always needed.

define view ZSalesOrderJoin as select from sales_order
inner join customer on sales_order.customer_id = customer.id
{
sales_order.id,
customer.name
}

Here, a real-time INNER JOIN is performed.

When to Use What?

Use Association:

When modeling data relationships.
When you want flexibility and better performance for optional fields.
When the associated data isn’t always needed.

Use Join:

When you always need data from both sources.
When performing aggregations or filters based on joined fields.
When doing complex multi-joins with specific types (e.g. inner join).

association – SAP EWM Help

Types of Association in CDS ?

Exposed Associations

Ad-hoc Associations

What is the difference between association vs Joins in CDS ?

When to Use What?