OCL Queries¶

OCL (Object Constraint Language) is a powerful query language for navigating and filtering objects in Bold. It's based on the OMG standard and provides a declarative way to express complex queries.

Basic Syntax¶

Important naming convention: In OCL, uppercase names like Customer refer to classes (metatypes), while lowercase names like orders refer to properties/associations on the current object. Customer.allInstances gets all Customer objects, while self.orders navigates from the current object to its orders.

Getting All Instances¶

Customer.allInstances

Navigating Associations¶

self.orders                    // One customer's orders
self.orders.orderLines         // All order lines from all orders

Filtering with Select¶

Customer.allInstances->select(age > 30)
Customer.allInstances->select(name = 'Acme')

Checking Existence¶

Customer.allInstances->select(orders->notEmpty)
Customer.allInstances->exists(totalPurchases > 10000)

Common Operations¶

Collection Operations¶

Operation	Type	Description	Example
`->select(expr)`	Collection	Filter elements	`orders->select(total > 100)`
`->reject(expr)`	Collection	Exclude elements	`orders->reject(cancelled)`
`->collect(expr)`	Collection	Transform elements	`orders->collect(total)`
`->exists(expr)`	Boolean	Any match?	`orders->exists(total > 1000)`
`->forAll(expr)`	Boolean	All match?	`orders->forAll(paid)`
`->isEmpty`	Boolean	Collection empty?	`orders->isEmpty`
`->notEmpty`	Boolean	Collection has items?	`orders->notEmpty`
`->size`	Integer	Count elements	`orders->size`
`->first`	Element	First element	`orders->first`
`->last`	Element	Last element	`orders->last`
`->at(n)`	Element	Element at index	`orders->at(0)`
`->includes(x)`	Boolean	Contains element?	`orders->includes(anOrder)`

Aggregation¶

orders->collect(total)->sum      // Sum of all totals
orders->collect(total)->avg      // Average
orders->collect(total)->max      // Maximum
orders->collect(total)->min      // Minimum

Sorting¶

Customer.allInstances->orderBy(name)
Customer.allInstances->orderDescending(createdDate)

Type Operations¶

Class Hierarchy Example¶

classDiagram
    Customer <|-- PremiumCustomer
    Customer <|-- RegularCustomer
    Customer : +name
    PremiumCustomer : +discountRate
    RegularCustomer : +loyaltyPoints

Type Checking Operations¶

self.oclIsKindOf(Customer)       // True for Customer, PremiumCustomer, RegularCustomer
self.oclIsTypeOf(Customer)       // True only for exact Customer type
self.oclAsType(PremiumCustomer)  // Cast to PremiumCustomer type

Using OCL in Delphi¶

Evaluate Expression¶

var
  Result: TBoldElement;
  Customers: TBoldObjectList;
begin
  Result := BoldSystem.EvaluateExpressionAsNewElement(
    'Customer.allInstances->select(orders->size > 5)',
    nil  // context object (self)
  );
  Customers := Result as TBoldObjectList;
end;

With Context Object¶

var
  Customer: TCustomer;
  OrderCount: Integer;
begin
  // 'self' refers to Customer
  OrderCount := BoldSystem.EvaluateExpressionAsInteger(
    'self.orders->size',
    Customer
  );
end;

In Bold Handles¶

// TBoldListHandle - for lists of objects
BoldListHandle1.Expression := 'Customer.allInstances->select(active)';

// TBoldExpressionHandle - for single values
BoldExpressionHandle1.Expression := 'self.orders->collect(total)->sum';

See TBoldListHandle and TBoldExpressionHandle for more details.

Advanced Examples¶

Complex Filtering¶

// Customers with at least one order over $1000 this year
Customer.allInstances->select(
  orders->exists(
    (total > 1000) and
    (orderDate.year = 2024)
  )
)

Note: Customer (uppercase) refers to the class/metatype, while orders (lowercase) is a navigation property on the current object. In OCL, Customer.allInstances accesses all instances of the Customer class, whereas self.orders navigates from the current object to its related orders.

// All products ordered by premium customers
Customer.allInstances
  ->select(oclIsKindOf(PremiumCustomer))
  ->collect(orders)
  ->collect(orderLines)
  ->collect(product)
  ->asSet

Conditional Logic¶

// If-then-else
if self.orders->isEmpty then
  'No orders'
else
  self.orders->size.toString + ' orders'
endif