Associations

Associations define relationships between entities. They determine how objects reference each other and control behavior on deletion.

Association Types

Type	MDL Keyword	Cardinality	Description
Reference	`Reference`	Many-to-One	Many objects on the FROM side reference one object on the TO side
ReferenceSet	`ReferenceSet`	Many-to-Many	Objects on both sides can reference multiple objects

CREATE ASSOCIATION

[/** <documentation> */]
CREATE ASSOCIATION <Module>.<Name>
  FROM <ParentEntity>
  TO <ChildEntity>
  TYPE <Reference|ReferenceSet>
  [OWNER <Default|Both|Parent|Child>]
  [DELETE_BEHAVIOR <behavior>]

Reference (Many-to-One)

A Reference association means each object on the FROM side can reference one object on the TO side. Multiple FROM objects can reference the same TO object.

/** Order belongs to Customer (many-to-one) */
CREATE ASSOCIATION Sales.Order_Customer
  FROM Sales.Customer
  TO Sales.Order
  TYPE Reference
  OWNER Default
  DELETE_BEHAVIOR DELETE_BUT_KEEP_REFERENCES;

ReferenceSet (Many-to-Many)

A ReferenceSet association allows multiple objects on both sides to reference each other:

/** Order has many Products (many-to-many) */
CREATE ASSOCIATION Sales.Order_Product
  FROM Sales.Order
  TO Sales.Product
  TYPE ReferenceSet
  OWNER Both;

Owner Options

The owner determines which side of the association can modify the reference.

Owner	Description
`Default`	Child (FROM side) owns the association
`Both`	Both sides can modify the association
`Parent`	Only parent (TO side) can modify
`Child`	Only child (FROM side) can modify

Delete Behavior

Controls what happens when an associated object is deleted.

Behavior	MDL Keyword	Description
Keep references	`DELETE_BUT_KEEP_REFERENCES`	Delete the object, set references to null
Cascade	`DELETE_CASCADE`	Delete associated objects as well

/** Invoice must be deleted with Order */
CREATE ASSOCIATION Sales.Order_Invoice
  FROM Sales.Order
  TO Sales.Invoice
  TYPE Reference
  DELETE_BEHAVIOR DELETE_CASCADE;

Naming Convention

Association names typically follow the pattern Module.FromEntity_ToEntity:

Sales.Order_Customer       -- Order references Customer
Sales.Order_Product        -- Order references Product
Sales.Order_Invoice        -- Order references Invoice

DROP ASSOCIATION

Remove an association:

DROP ASSOCIATION Sales.Order_Customer;

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