TBoldListHandle¶

TBoldListHandle is used to get a list from a root using an OCL expression

Declaration¶

TBoldListHandle = class(TBoldCursorHandle, IBoldOCLComponent)

Hierarchy¶

Description¶

A TBoldListHandle is used to represent a list obtained by applying an OCL expression relative to the value of a TBoldElementHandle that is set using the RootHandle.

A handle can keep it's value current by using the subscription mechanism in Bold. This behavior is controlled by the Subscribe property.

The list is obtained by calling GetAsList on the value obtained by evaluating Expression. This means that if the result of the evaluation is an individual element rather than a List, a list of one element will be created.

The list may be further modified by a filtering and/or sorting. This is done by setting the BoldFilter and/or BoldComparer properties.

The list will in most cases be a list of Business Objects (TBoldObject), but can be a list of any TBoldElement, e.g. a list of strings (TBAString).

In addition to keeping a list, a TBoldListHandle also holds a current position in the list. The Value property will be this element, rather that the whole list. The list itself can be accessed through the list property.

Usage

The most common use of the component is placing it on a form or datamodule, connecting its RootHandle to another handle, and setting the expression.

It can now be used by connecting Bold-aware controls to it. If it is connected to a multi-valued control, such as a TBoldGrid, the elements of its List will be displayed. If it is connected to a single-valued control, such as a TBoldEdit, Value, i.e. CurrentElement, will be displayed in the control.

It can also be used by other handles. In this case they will be evaluated relative to Value.

Implementation notes

Like all handles, TBoldListHandle acts as an adapter between the business object/server world and the IDE/Client world.

TBoldListHandle has a rather complex internal structure. Depending on the properties it will internally aggregate other handles to perform OCL-evaluation, sorting and filtering.

Properties¶

Name	Summary	Notes
BoldComparer	Optional reordering/sorting component
BoldFilter	Optional filter component
EvaluateInPS	If Expression should be evaluated in the database, or in memory.
Expression	OCL expression to evaluate the resulting list element
MutableListExpression	List expression yielding mutable list
Variables	Allows the expression to have more than one context

BoldComparer¶

property BoldComparer: TBoldComparer;

Setting the BoldComparer property will use the comparer to sort the list produced by Expression.

Note

Note that a sorted list is regarded as derived and may therefore not be modified. However, the `MutableList` property will understand the concept of comparers, and can be used for some list-manipulations

Note

In most cases sorting can be done directly in `Expression`, by using BoldSoft's extensions to OCL. This often more efficient convenient, and should be done whenever possible.

BoldFilter¶

property BoldFilter: TBoldFilter;

Setting the BoldFilter property will apply the filter to the list produced by Expression.

Note

A filtered list is regarded as derived and may therefore not be modified.

Note

In most cases filtering can be done directly in `Expression`. This is often far more convenient, and should be done whenever possible.

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

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

For further information, see Ocl2Sql

Expression¶

property Expression: TBoldExpression;

Expression is a string containing an OCL expression. The list of the handle is defined by evaluating Expression with BoldHandle.Value as the context, and then calling AsList.

At design-time the property editor provides support in writing the expression.

MutableListExpression¶

property MutableListExpression: TBoldExpression;

The list as described by the Expression may be immutable, i.e. not possible to change. This is the case of any any kind of derived lists; Person.allInstances->orderBy(firstName).

If a TBoldNavigator is connected to the list handle, it will not be possible to add objects to the list by pressing the [+] button, nor delete objects by pressing the [-] button. To overcome this, specify an expression yielding a mutable list; Person.allInstances. This expression will be used if the list produced by the Expression-property is immutable.

The resulting mutable list is accessible via the MutableList property.

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 instance of TBoldListHandle	override
Destroy	Destroys an instance of TBoldListHandle	override
GetMutableList	Overrides TBoldAbstractListHandle.GetMutableList	protected, override
GetRootHandle	Overrides TBoldRootedHandle.GetRootHandle	protected, override
Loaded	Overrides TComponent.Loaded	protected, override
MarkOutOfDate	Forces a refresh of the value	override
Notification	Overrides TComponent.Notification	protected, override
RefersToComponent	Determines if this instance of TBoldListHandle in some way is referring to the component passed as parameter.	override
SetRootHandle	Overrides TBoldRootedHandle.SetRootHandle	protected, override
SetStaticSystemHandle	Overrides TBoldNonSystemHandle.SetStaticSystemHandle	protected, override
SetSubscribe	Overrides TBoldRootedHandle.SetSubscribe	protected, override

Create¶

constructor Create(Owner: TComponent); override; See also Ancestor Method

Use Create to create an instance of TBoldListHandle.

Destroy¶

destructor Destroy; override; See also Ancestor Method

Do not call Destroy, call Free instead.

GetMutableList¶

function GetMutableList: TBoldList; override; See also Ancestor Method

Overrides GetMutableList

GetRootHandle¶

function GetRootHandle: TBoldElementHandle; override; See also Ancestor Method

Overrides GetRootHandle

Loaded¶

procedure Loaded; override; See also Ancestor Method

Overrides TComponent.Loaded

MarkOutOfDate¶

procedure MarkOutOfDate; override; See also Ancestor Method

Call MarkOutOfDate to force the component to refresh its value.

Notification¶

procedure Notification(AComponent: TComponent; Operation: TOperation); override;

Overrides TComponent.Notification

RefersToComponent¶

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

Determines if this instance of TBoldListHandle in some way is referring to the component passed as parameter.

SetRootHandle¶

procedure SetRootHandle(const Value: TBoldElementHandle); override; See also Ancestor Method

Overrides SetRootHandle

SetStaticSystemHandle¶

procedure SetStaticSystemHandle(Value: TBoldAbstractSystemHandle); override; See also Ancestor Method

Overrides SetStaticSystemHandle

SetSubscribe¶

procedure SetSubscribe(Value: Boolean); override; See also Ancestor Method

Overrides SetSubscribe

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