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WOAssociation
Inherits from: Object
Implements: Cloneable
Package: com.webobjects.appserver
Class Description
The WOAssociation class declares the programmatic interface to objects that represent the values of WebObject attributes, as specified in a declarations file. You rarely need to create subclasses of WOAssociation, except in situations where you need to subclass WODynamicElement.
The purpose of a WOAssociation object is to provide a unified interface to values of different types. For example, consider these declarations:
TREENAME1:WOString {value = "Ash"}; TREENAME2:WOString {value = treeName}; TREENAME3:WOString {value = selectedTree.name};
At runtime, the WebObjects parser scans an HTML template and these declarations and creates three WOString dynamic element objects. In the first case, the WOString's value attribute is assigned a constant string. In the second, it's associated with the treeName variable of the component in which the dynamic element is declared. In the third, value is associated with the name attribute of the component's selectedTree variable. The search path for the value can be arbitrarily deep, depending on the needs of your application:
MAYOR:WOString {value = country.state.city.mayor.name};
To resolve a path such as this, WebObjects accesses each part in turn. First, it looks for the component's country variable. If the component responds to a country message, it sends one to determine the value; otherwise, it directly accesses the component's country instance variable to determine the value. Next, it checks the country object for a state attribute, using the same strategy of looking for an accessor method named state and then, if necessary, accessing the state variable's value directly. It continues in this way until the ultimate value is determined.
WOAssociation objects present the WebObjects framework with a unified interface to attribute values, whether their values are static or dynamic. The value attribute for TREENAME1 in the example above will never change during the course of program execution, but the other WOStrings have values that are potentially dynamic, and so will have to be determined at runtime. Since the value of any WOAssociation can be determined by sending it a valueInComponent message, objects that use WOAssociation objects don't have to be concerned with how values are resolved. The WODynamicElement class makes extensive use of this feature. See the WODynamicElement class specification for more information.
Method Types
Creation associationWithKeyPath associationWithValue Obtaining association attributes bindingInComponent booleanValueInComponent isValueConstant isValueConstantInComponent isValueSettable isValueSettableInComponent keyPath Setting and retrieving value setValue valueInComponent Debugging setDebugEnabledForBinding
Constructors
WOAssociation
protected WOAssociation()
Static Methods
associationWithKeyPath
public static WOAssociation associationWithKeyPath(String aKeyPath)
TREENAME3:WOString {value = selectedTree.name};
it invokes associationWithKeyPath to create a WOAssociation whose key is "selectedTree.name". When the resulting WOAssociation is asked for its value, it searches for the value of the name attribute of in the current component's selectedTree attribute.
If aKeyPath is null, the value of the WOAssociation is also null.
See Also: associationWithValue
associationWithValue
public static WOAssociation associationWithValue(Object aValue)
TREENAME3:WOString {value = "Time Flies!"};
it invokes this method to create a WOAssociation whose value is "Time Flies!".
See Also: associationWithKeyPath
Instance Methods
bindingInComponent
public abstract String bindingInComponent(WOComponent aComponent)
booleanValueInComponent
public boolean booleanValueInComponent(WOComponent aComponent)
false
if the binding is to a boolean variable or constant with a value of false
, the binding is to a null value, the binding is to a numeric value equivalent to zero, the binding is to a string that can be interpreted as a number whose value is zero, or the binding is to a string whose value is "false" or "no" (independent of case). Otherwise, this method returns true
.
isValueConstant
public boolean isValueConstant()
See Also: associationWithValue, isValueSettable
isValueConstantInComponent
public boolean isValueConstantInComponent(WOComponent aComponent)
See Also: associationWithValue, isValueSettableInComponent
isValueSettable
public boolean isValueSettable()
See Also: associationWithKeyPath, isValueConstant
isValueSettableInComponent
public boolean isValueSettableInComponent(WOComponent aComponent)
See Also: associationWithKeyPath, isValueConstant
keyPath
public abstract String keyPath()
setDebugEnabledForBinding
public void setDebugEnabledForBinding(String aBindingName, String aDeclarationName, String aDeclarationType)
setValue
public void setValue( Object aValue, WOComponent aComponent)
Finds the attribute of aComponent pointed to by the left-hand-side of the receiver and sets its value to aValue. This method throws an exception if the receiver's value is not settable. For example, sending a setValue message to a WOAssociation created from this declaration,
USER:WOTextField {value = userName};
sets the current component's userName variable to the value typed into the WOTextField.
One way in which the WebObjects framework uses this method is to synchronize the values of nested components. When attributes in child and parent components are associated with one another and changes occur in one component, this method is invoked to migrate those changes to the other component. See the reusable components chapter in the WebObjects Developer's Guide for more information.
See Also: valueInComponent
toString
public String toString()
valueInComponent
public Object valueInComponent(WOComponent aComponent)
DOWNPAYMENT:WOString {value = downpayment};
returns the value of the current component's downpayment variable.
Sending a value message to a WOAssociation created from this declaration,
DOWNPAYMENT:WOString {value = "$5000.00"};
returns the value "$5000.00" (independent of the current component).
This method raises an exception if it cannot resolve the WOAssociation's value with the current component.
One way in which the WebObjects framework uses this method is to synchronize the values of nested components. When attributes in child and parent components are associated with one another and changes occur in one component, this method is invoked to migrate those changes to the other component. See the reusable components chapter in the WebObjects Developer's Guide for more information.
See Also: setValue
© 2001 Apple Computer, Inc. (Last Published April 15, 2001)