TBoldExpressionHandle¶

A handle that uses an OCL expression to evaluate a value from its root handle.

Declaration¶

TBoldExpressionHandle = class(TBoldRootedHandle, IBoldOCLComponent)

Hierarchy¶

Description¶

TBoldExpressionHandle is a subclass of TBoldRootedHandle and everything in its description applies and is for the most part not repeated here.

Value
The value of the handle is defined by evaluating Expression with RootHandle.Value as the context.

Typing
The StaticBoldType of the handle is defined as the type of Expression in the context of StaticRootType. If the handle is connected to another handle StaticRootType will the the StaticBoldType of that handle, otherwise it will be determined through RootTypeName.

Bold Events
TBoldExpressionHandle is a subclass of TBoldSubscribableComponent, and can therefor by subscribed to using AddSmallSubscription. A TBoldExpressionHandle can send the following events:

beDestroying: Sent when the handle is about to be destroyed.
beValueIdentityChanged: Sent when Value has changed, i.e. when Value points to a new TBoldElement. Also sent if anything influencing StaticBoldType has changed.

Due to the lazy evaluation, "has changed" has a very specific meaning. It means that the next time the Value property is accessed it may return a different value from the previous time. It does not imply that this value has actually been calculated yet.

If several things occur that would change Value, but the Value property is not accessed in between, only the first will give rise to a beValueIdentityChanged event.

Note

The ValueIdentityChanged event is not sent when the contents of Value is changed. This is found out by subscribing to Value itself.

Properties¶

Name	Summary	Notes
EvaluateInPS	If the expression should be evaluated in the database, instead of in memory
Expression	Expression is a string containing an OCL expression.
Variables	Allows the expression to have more than one context

EvaluateInPS¶

property EvaluateInPS: Boolean;

Normally OCL expressions are evaluated in memory, but this can lead to great inefficiencies when numerous objects have to be loaded. If this property is set to true an attempt to execute the expression directly in the database will be made. If this fails, there will be an exception.

Note that if the expression is executed directly against the database, the result will be determined by the contents of the database, and any uncommited data in the object space will be disregarded.

Note

If this property is true, the component will ignore the setting of Subscribe.

For further information, see Ocl2Sql

Expression¶

property Expression: TBoldExpression;

The Value of the Handle is defined by evaluating Expression with RootHandle.Value as the context.

At design-time the property editor provides support in writing the expression, provided that either the handle is connected to another handle, or that RootTypeName (and optionally StaticSystemHandle) is set.

Bold Events
Since changing Expression indirectly changes Value the following events can be sent when setting Expression

beValueIndentityChanged: Sent if Expression is assigned a new value.

If the property is assigned with the same value as it already has the event will not be sent.

Also, the event will not be sent if it has previously been sent, and the Value property has not been accessed since then.

Variables¶

property Variables: TBoldOclVariables;

If the OCL expression requires more than one context, additional context must be imported using a TBoldOclVariables component

Methods¶

Name	Summary	Notes
create	Creates an instanc of TBoldExpressionHandle	override
DeriveAndSubscribe		protected, override
destroy	Destroys an instance of a TBoldExpressionHandle.	override
GetStaticBoldType		protected, override
RefersToComponent	Determine if there is a relationship to the component passed as parameter.	override

create¶

constructor create(owner: TComponent); override; See also Ancestor Method

Use Create to create an instance of TBoldExpressionHandle.

DeriveAndSubscribe¶

procedure DeriveAndSubscribe(DerivedObject: TObject; Subscriber: TBoldSubscriber); override; See also Ancestor Method

destroy¶

destructor destroy; override; See also Ancestor Method

Do not call Destroy directly, use Free.

GetStaticBoldType¶

function GetStaticBoldType: TBoldElementTypeInfo; override; See also Ancestor Method

RefersToComponent¶

function RefersToComponent(Component: TBoldSubscribableComponent): Boolean; override; See also Ancestor Method

RefersToComponent determins if there is a relationship between the TBoldExpressionHandle and the component passed as parameter. It is used internally to avoid circular dependencies between components.

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