EOKeyValueCoding

Implemented by:

EOKeyValueCodingAdditions

EOEnterpriseObject

EOCustomObject

EOGenericRecord

Implements:

(com.apple.client.eocontrol only) NSKeyValueCoding

Package:

com.apple.client.eocontrol

com.apple.yellow.eocontrol

Interface Description

The EOKeyValueCoding interface defines Enterprise Objects Framework's main data transport mechanism, in which the properties of an object are accessed indirectly by name (or key), rather than directly through invocation of an accessor method or as instance variables. Thus, all of an object's properties can be accessed in a consistent manner. EOCustomObject and EOGenericRecord provide default implementations of EOKeyValueCoding, which are sufficient for most purposes.

The basic methods for accessing an object's values are takeValueForKey, which sets the value for the property identified by the specified key, and valueForKey, which returns the value for the property identified by the specified key. The default implementations provided by EOCustomObject use the accessor methods normally implemented by objects (or to access instance variables directly if need be), so that you don't have to write special code simply to integrate your objects into the Enterprise Objects Framework.

The corresponding methods takeStoredValueForKey and storedValueForKey are similar, but they're considered to be a private API, for use by the Framework for transporting data to and from trusted sources. For example, takeStoredValueForKey is used to initialize an object's properties with values fetched from the database, whereas takeValueForKey is used to modify an object's properties to values provided by a user or other business logic. How these methods work and how they're used by the framework is discussed in more detail in the section "Stored Value Methods".

The remaining methods, handleQueryWithUnboundKey, handleTakeValueForUnboundKey, and unableToSetNullForKey, are provided to handle error conditions. The default versions of handleQueryWithUnboundKey and handleTakeValueForUnboundKey throw an exception.

For more information on EOKeyValueCoding, see the sections:

• "Stored Value Methods"
• "Type Checking and Type Conversion"

Constants

EOKeyValueCoding defines the following int constants to be used as possible arguments for the createKeyValueBindingForKey and keyValueBindingForKey methods. The argument indicates whether the return value, a EOKeyValueCoding.KeyBinding object, binds a class/key pair to a mechanism to set the value for a key or to retrieve it.

Interfaces Implemented

NSKeyValueCoding (com.apple.client.eocontrol only)

takeValueForKey

valueForKey

Method Types

Accessing values

storedValueForKey

takeStoredValueForKey

takeValueForKey

valueForKey

Handling error conditions

handleQueryWithUnboundKey

handleTakeValueForUnboundKey

unableToSetNullForKey

Instance Methods

handleQueryWithUnboundKey

public abstract Object handleQueryWithUnboundKey(String key)

handleTakeValueForUnboundKey

public abstract void handleTakeValueForUnboundKey( Object value, String key)

storedValueForKey

public abstract Object storedValueForKey(String key)

1. Searches for a private accessor method based on key (a method preceded by an underbar). For example, with a key of "lastName", storedValueForKey looks for a method named _getLastName or _lastName.
2. If a private accessor isn't found, searches for an instance variable based on key and returns its value directly. For example, with a key of "lastName", storedValueForKey looks for an instance variable named _lastName or lastName.
3. If neither a private accessor or an instance variable is found, storedValueForKey searches for a public accessor method based on key. For the key "lastName", this would be getLastName or lastName.
4. If key is unknown, storedValueForKey calls handleTakeValueForUnboundKey.

This different search order allows an object to bypass processing that is performed before returning a value through public API. However, if you always want to use the search order in valueForKey, you can implement the static method useStoredAccessor to return false. And as with valueForKey, you can prevent direct access of an instance variable with the method the static method accessInstanceVariablesDirectly.

takeStoredValueForKey

public abstract void takeStoredValueForKey( Object value, String key)

1. Searches for a private accessor method based on key (a method preceded by an underbar). For example, with a key of "lastName", takeStoredValueForKey looks for a method named _setLastName.
2. If a private accessor isn't found, searches for an instance variable based on key and sets its value directly. For example, with a key of "lastName", takeStoredValueForKey looks for an instance variable named _lastName or lastName.
3. If neither a private accessor or an instance variable is found, takeStoredValueForKey searches for a public accessor method based on key. For the key "lastName", this would be setLastName.
4. If key is unknown, takeStoredValueForKey calls handleTakeValueForUnboundKey.

This different search order allows an object to bypass processing that is performed before setting a value through public API. However, if you always want to use the search order in takeValueForKey, you can implement the static method useStoredAccessor to return false. And as with valueForKey, you can prevent direct access of an instance variable with the method the static method accessInstanceVariablesDirectly.

takeValueForKey

public abstract void takeValueForKey( Object value, String key)

The default implementation provided by EOCustomObject works as follows:

1. Searches for a public accessor method of the form set Key , invoking it if there is one.
2. If a public accessor method isn't found, searches for a private accessor method of the form _set Key , invoking it if there is one.
3. If an accessor method isn't found and the static method accessInstanceVariablesDirectly returns true, takeValueForKey searches for an instance variable based on key and sets the value directly. For the key "lastName", this would be _lastName or lastName.
4. If neither an accessor method nor an instance variable is found, the default implementation invokes handleTakeValueForUnboundKey.

unableToSetNullForKey

public abstract void unableToSetNullForKey(String key)

valueForKey

public abstract Object valueForKey(String key)

The default implementation provided by EOCustomObject works as follows:

1. Searches for a public accessor method based on key. For example, with a key of "lastName", valueForKey looks for a method named getLastName or lastName.
2. If a public accessor method isn't found, searches for a private accessor method based on key (a method preceded by an underbar). For example, with a key of "lastName", valueForKey looks for a method named _getLastName or _lastName.
3. If an accessor method isn't found and the static method accessInstanceVariablesDirectly returns true, valueForKey searches for an instance variable based on key and returns its value directly. For the key "lastName", this would be _lastName or lastName.
4. If neither an accessor method nor an instance variable is found, the default implementation invokes handleQueryWithUnboundKey.