Database Reference
In-Depth Information
-setValue:forUndefinedKey:
- (
void
)setValue:(id)value forUndefinedKey:(NSString*)key
{
[self willChangeValueForKey:key];
NSManagedObject *parameter = [self findParameter:key];
if
(!parameter) {
if
([[self defaults] valueForKey:key] &&
[value isEqualTo:[[self defaults] valueForKey:key]]) {
[self didChangeValueForKey:key];
return
;
}
parameter = [self createParameter:key];
}
else
{
if
([[self defaults] valueForKey:key] &&
[value isEqualTo:[[self defaults] valueForKey:key]]) {
[self willChangeValueForKey:key];
[[[self associatedDocument] managedObjectContext] deleteObject:parameter];
[self didChangeValueForKey:key];
return
;
}
}
if
([value isKindOfClass:[NSNumber class]]) {
[parameter setValue:[value stringValue] forKey:@
"value"
];
}
else if
([value isKindOfClass:[NSDate class]]) {
[parameter setValue:[value description] forKey:@
"value"
];
}
else
{
[parameter setValue:value forKey:@
"value"
];
}
[self didChangeValueForKey:key];
}
In addition to being able to access a parameter, we also need to set parameters.
This is done in the counterpart method of
-valueForUndefinedKey:
called
-setVal-
ue:forUndefinedKey:
. In this method, we first notify the system we are going to be
changing the value associated with the passed-in key. This is part of
KVO
and
is required so that notifications work correctly. After starting the
KVO
notifi-
cation, we attempt to retrieve the
NSManagedObject
from the parameters table.
If there is no
NSManagedObject
for the passed-in key, we check the
defaults
NSDictionary
to see whether there is a default. If there is a default set and the
passed-in value matches the default, we complete the
KVO
notification and
return. If the default value does not match the passed-in value, we create a
new
NSManagedObject
for the passed-in key.
If there is an
NSManagedObject
and a default set for the key, we compare the
default value to the passed-in value. If they match, we
delete
the
NSManagedOb-
ject
, which effectively resets the parameter to the default. Once we pass the
