Currently I have several instances where I need to send a group of objects to the server:
{
"things": [
{
//object stuff
},
{
//object stuff
},
...
]
}
So what I've been doing is defining an intermediate object MyThingPayload
#interface MyThingPayload
#property (nonatomic, strong) NSArray *things;
#end
And then when mapping
RKObjectMapping *mapping = [RKObjectMapping mappingForClass:NSClassFromString(#"MyThingPayload")];
[mapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:#"things"
toKeyPath:#"things"
withMapping:[self entityMappingForManagedThingObject]]];
Seems like unnecessary overhead. Is there a way to do this without the intermediate object that holds an array?
You need an intermediate object to provide the structure to be used during serialisation. It doesn't need to be a custom class though, it can just be an NSDictionary containing the correct key and NSArray value.
Related
I am trying to map objects from two separate json files (while seeding an sqlite db with RestKit). The files are connected by a foreign id file1Code.
The structure looks like this:
File 1:
[ {
"code": "1",
"activ": false,
"name": "Joe"
},
{
"code": "2",
"activ": false,
"name": "John"
}
]
File 2:
[
{
"code": 666000,
"name": "Hausarzt",
"file1Code": "1",
"activ": false
}
]
Entity for File 1 looks like this:
#interface File1Entity : KeyTab
Entity for File 2 looks like this:
#interface File2Entity : KeyTab
#property (nonatomic, retain) File1Entitiy *file1Obj;
// Transient
#property (nonatomic, retain) NSNumber *file1Code;
KeyTab (from which both inherit) looks like this:
#interface KeyTab : NSManagedObject
#property (nonatomic, retain) NSNumber * code;
#property (nonatomic, retain) NSString * name;
#property (nonatomic, retain) NSNumber * activ;
Now I am trying to use the "Connecting Non-Nested Relationships Using Foreign Keys" from the RestKit documentation found here.
I am using addConnectionForRelationship like this:
[file2EntityMapping addConnectionForRelationship:#"file1Obj"
connectedBy:#{#"file1Code": #"code"}];
But get the error message "Cannot connect relationship: invalid attributes given for source entity" since file1Obj is a property and not an attribute.
Is this the right way to do this in RestKit?
You need to add file1Code as a transient attribute on File2Entity and set it during the mapping. The foreign key connection is completed after the mapping so the original JSON is no longer available (hence the error that the data doesn't exist).
I'm a newcomer to Cocoa programming, having never got into Objective-C. Now, I am trying to learn it with Swift by going through the Aaron Hillegrass book “Cocoa Programming for Mac OS X, 4e" and implementing everything there in Swift instead of Obj-C. It has been going okay so far, but I hit a roadblock in Chapter 8 (the RaiseMan application).
Here is the Objective-C code from the book:
The header:
#import <Foundation/Foundation.h>
#interface Person : NSObject {
NSString *personName;
float expectedRaise;
}
#property (readwrite, copy) NSString *personName;
#property (readwrite) float expectedRaise;
#end
And here is the implementation
#import "Person.h"
#implementation Person
#synthesize personName;
#synthesize expectedRaise;
- (id)init
{
self = [super init];
if (self) {
expectedRaise = 0.05;
personName = #"New Person";
}
return self;
}
#end
You are then supposed to go to Interface Builder, get an Array Controller, specify Person as its class, and add personName and expectedRaise as its keys.
I rewrote the Person class in Swift as follows:
import Cocoa
class Person: NSObject {
var personName = String()
var expectedRaise = Float()
}
and connected it to the ArrayController as the book told me to.
There is also some code in the Document file:
init() {
employees = NSMutableArray()
println("hi")
super.init()
// Add your subclass-specific initialization here.
var p = Person()
p.personName = "New Person"
p.expectedRaise = 0.05
}
Here is what the interface looks like (SO won't let me post it directly) https://www.dropbox.com/s/e5busxes9ex3ejd/Screenshot%202014-06-13%2019.02.37.png
When I try to run the app and click the "add employees" button, I get this error in the console:
"RaiseMan[9290:303] Cannot find object class with name Person"
So, my question is: what am I doing wrong?
Short answer: you need to specify the class namespace (module name) in Interface Builder: RaiseMan.Person
Details and other options:
This is because Swift adds a prefix to the name of every class injected into the Objective-C runtime in order to avoid name collisions. The prefix follows this convention: _TtC$$AppName%%ClassName, where $$ is the length of AppName and %% is the length of ClassName (see this other SO question for more info).
So in order for the array controller to be able to instantiate the Person class, you need to provide the mangled name in Interface Builder: _TtC8RaiseMan6Person.
Another option is to provide an explicit Objective-C name for your Swift class by using the #objc(<#name#>) attribute:
#objc(Person)
class Person: NSObject {
}
In that case, you can provide the name specified in your #objc attribute to Interface Builder (e.g. Person). See the Using Swift with Cocoa and Objective-C guide for more details.
If I'm reading your example right, and assuming your init() method belongs in the Person class, you need to put the init() method inside the class braces.
Also, declare variables of a certain type with the following format:
var/let (name): (type)(optional)
So, for your example, you would instead have for the Person class:
class Person {
var personName: String
var expectedRaise: Float?
init() {...}
}
You don't necessarily have to subclass from NSObject if you don't need to; in Swift objects don't have to subclass from NSObject (or another parent) if they don't require it. And the "Float?" means that it is of type Optional Float, meaning that it is a Float that may have a value, or it may have no value, depending if the person is expected to get a raise or not (or you may not want it Optional and just set the value to 0).
Keep in mind, if you have multiple build targets, every new class you create needs to be added to that build target. If you don't have its target membership set to the build target, Swift will not find the class file.
I currently have a cardType attribute on my entity, which in the old model could be "Math", "Image" or "Text". In the new model, I'll be using just "Math" and "Text" and also have a hasImage attribute, which I want to set to true if the old cardType was Image (which I want to change to "Text").
Lastly, I have a set of another entity, "card", of which a set can be associated with a deck, and in each of those, I'll also have hasImage which I want to set to true if the deck was of "Image" type before.
Is this all possible using the Value Expression in the Mapping Model I've created between the two versions, or will I have to do something else?
I can't find any document telling me exactly what is possible in the Value Expression (Apple's doc - http://developer.apple.com/library/mac/#documentation/cocoa/conceptual/CoreDataVersioning/Articles/vmMappingOverview.html%23//apple_ref/doc/uid/TP40004735-SW3 - only has a very simple transformation). If I have to do something else, what would that be? This seems simple enough that an expression should be able to do it.
One thing you can do is create a custom migration policy class that has a function mapping your attribute from the original value to a new value. For example I had a case where I needed to map an entity called MyItems that had a direct relationship to a set of values entities called "Items" to instead store an itemID so I could split the model across multiple stores.
The old model looked like this:
The new model looks like this:
To do this, I wrote a mapping class with a function called itemIDForItemName and it was defined as such:
#interface Migration_Policy_v1tov2 : NSEntityMigrationPolicy {
NSMutableDictionary *namesToIDs;
}
- (NSNumber *) itemIDForItemName:(NSString *)name;
#end
#import "Migration_Policy_v1tov2.h"
#implementation Migration_Policy_v1tov2
- (BOOL)beginEntityMapping:(NSEntityMapping *)mapping manager:(NSMigrationManager *)manager error:(NSError **)error {
namesToIDs = [NSMutableDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:1],#"Apples",
[NSNumber numberWithInt:2],#"Bananas",
[NSNumber numberWithInt:3],#"Peaches",
[NSNumber numberWithInt:4],#"Pears",
[NSNumber numberWithInt:5],#"Beef",
[NSNumber numberWithInt:6],#"Chicken",
[NSNumber numberWithInt:7],#"Fish",
[NSNumber numberWithInt:8],#"Asparagus",
[NSNumber numberWithInt:9],#"Potato",
[NSNumber numberWithInt:10],#"Carrot",nil];
return YES;
}
- (NSNumber *) itemIDForItemName:(NSString *)name {
NSNumber *iD = [namesToIDs objectForKey:name];
NSAssert(iD != nil,#"Error finding ID for item name:%#",name);
return iD;
}
#end
Then for the related Mapping Name for the attribute in your mapping model you specify the Value Expression as the result of your function call as such:
FUNCTION($entityPolicy,"itemIDForItemName:",$source.name) **
You also have to set the Custom Policy Field of your Mapping Name for that attribute to your mapping class name (in this case Migration_Policy_v1tov2).
**note this should match the selector signature of the method
Imagine an CoreData entity (e.g. named searchEngine).
NSManagedObjectContext manages some "instances" of this entity.
The end-user is going to be able to select his "standard searchEngine" with a NSPopupButton.
The selected object of NSPopupButton should be binded to the NSUserDefaults.
The problem:
1) #try{save}
a) If you try to save the selected "instance" directly to NSUserDefaults there comes something like this:-[NSUserDefaults setObject:forKey:]: Attempt to insert non-property value ' (entity: searchEngine; id: 0x156f60 ; data: {
url = "http://google.de/";
someAttribute = 1;
name = "google";
})' of class 'searchEngine'.
b) If you try to convert the "instance" to NSData comes this:-[searchEngine encodeWithCoder:]: unrecognized selector sent to instance 0x1a25b0
So any idea how to get this entities in a plist-compatible data?
2) #try{registerDefaults}
Usually the registerDefaults: method is implemented in + (void)initialize. The problem here is that this method is called before CoreData loads the saved entities from his database. So I can't set a default to a no-existing object, right?
I know, long questions... but: try{[me provide:details]} ;D
If you need to store a reference to a specific managed object, use the URI representation of its managed object ID:
NSURL *moIDURL = [[myManagedObject objectID] URIRepresentation];
You can then save the URL to user defaults.
To retrieve the managed object, you use:
NSManagedObjectID *moID = [myPersistentStoreCoordinator managedObjectIDForURIRepresentation:moIDURL];
NSManagedObject *myManagedObject = [myContext objectWithID:moID];
The only caveat is that you must ensure that the original managed object ID is permanent -- this is not a problem if you've already saved the object, alternatively you can use obtainPermanentIDsForObjects:error:.
Here's the cleanest and shortest way to currently do this using the setURL and getURL methods added in 4.0 to avoid extra calls to NSKeyedUnarchiver and NSKeyedArchiver:
Setter:
+ (void)storeSomeObjectId:(NSManagedObjectID *)objectId
{
[[NSUserDefaults standardUserDefaults] setURL:[objectId URIRepresentation]
forKey:#"someObjectIdKey"];
[[NSUserDefaults standardUserDefaults] synchronize];
}
Getter:
+ (SomeManagedObject *)getObjectByStoredId
{
NSURL *uri = [[NSUserDefaults standardUserDefaults] URLForKey:#"someObjectIdKey"];
NSManagedObjectID *objectId = [self.persistentStoreCoordinator managedObjectIDForURIRepresentation:uri];
SomeManagedObject *object = [self.managedObjectContext objectWithID:objectId];
}
You wouldn't want to try and archive a core data entity and store it. Instead, you would store the key or some other known attribute and use it to fetch the entity when the application starts up.
Some example code (slightly modified from the example posted in the Core Data Programming Guide):
NSManagedObjectContext *moc = [self managedObjectContext];
NSEntityDescription *entityDescription = [NSEntityDescription
entityForName:#"SearchEngine" inManagedObjectContext:moc];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:entityDescription];
NSPredicate *predicate = [NSPredicate predicateWithFormat:
#"engineName LIKE[c] '%#'", selectedEngineName];
[request setPredicate:predicate];
NSError *error = nil;
NSArray *array = [moc executeFetchRequest:request error:&error];
if (array == nil)
{
// Deal with error...
}
This way you save the name in the user defaults and fetch the entity when necessary.
My model saves the record's UUID to the UserDefaults in order to launch the last opened record in the next app launch.
public class Patient: NSManagedObject {
override public func awakeFromInsert() {
super.awakeFromInsert()
uuid = UUID()
}
extension Patient {
#NSManaged public var uuid: UUID
#NSManaged ...
}
It is a good practice to identify each record with an unique ID (UUID). You can save the UUID as string simply calling uuid.uuidString.
I have replaced an NSTextField with an NSTokenField so that I can perform some auto-completion. The value of the NSTextField was bound to a NSString attribute of a controller class. Now that I have changed the NSTextField to an NSTokenField the value has changed to an NSArray.
How do I make the NSTokenField value binding be an NSString?
The changing of the value from an NSString to an NSArray seems like bad OO design. I though that a subclass should be able replace a superclass without any modifications to the subclass.
If all you want is autocompletion, and not tokenization, you can achieve this by using a plain NSTextField and implementing the delegate method:
- (NSArray *)control:(NSControl *)control textView:(NSTextView *)textView completions:(NSArray *)words forPartialWordRange:(NSRange)charRange indexOfSelectedItem:(NSInteger *)index
(This method is actually declared in NSControl, NSTextField's superclass.)
If you do want to have tokenization, then you will have to provide an NSArray for the object value to be displayed in the token field. As explained in the NSTokenField programming guide, the array you provide will be a mix of strings and objects. Strings will be displayed as-is, and any non-string objects will be displayed as tokens in the token field. You would need to implement the various NSTokenField delegate methods to provide a string to be displayed for each represented object in your array.
It does appear that the Cocoa Bindings Reference states that the object bound to the value of an NSTokenField should be a string or number, but in my experience, this is incorrect, and the token field should be bound to an NSArray, just like when using setObjectValue:
You can subclass your own NSValueTransformer and set it in your binding.
NSTokenField's value binding accepts an NSString or NSNumber binding, not an NSArray. How have you determined that it is wanting an NSArray?
The best way to do this (as Cocoafan pointed out) is to use Value Transformers. Value transformers allow you convert the object-type used your model into a type that's suitable for a view. Here is a very simple String/Array transformer that allows you to store your data as a comma separated string but will convert it back and forth to an array of strings.
#interface StringArrayTransformer: NSValueTransformer {}
#end
#implementation StringArrayTransformer
+ (Class)transformedValueClass { return [NSString class]; }
+ (BOOL)allowsReverseTransformation { return YES; }
- (id)transformedValue:(id)value {
NSString *string = (NSString*) value;
return [string componentsSeparatedByString:#", "];
}
-(id)reverseTransformedValue:(id)value {
NSArray *array = (NSArray*)value;
return [array componentsJoinedByString:#", "];
}
#end
If you're using bindings for your NSTokenField then to use this the transformer simply select the NSTokenField in Interface Builder, then in the Bindings Inspector on the right hand side, for the Value binding, set the "Value Transformer" to StringArrayTransformer as per below.