RestKit - Object Manager

Episode #53 | 18 minutes | published on February 14, 2013

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This episode covers some additional pieces of RestKit, abstracting network requests even further by providing a route & mapping for a given object and utilizing RKObjectManager to perform the work for us. Instead of using a live API, we verify the behavior using SenTestingKit.

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Our Data Model

For this example we will work with a simple domain model representing a wiki.

@interface WKCategory : NSObject

@property (nonatomic, copy) NSString *name;

@end

@interface WKWikiPage : NSObject

@property (nonatomic, assign) NSInteger pageID;
@property (nonatomic, strong) NSString *title;
@property (nonatomic, strong) NSString *body;
@property (nonatomic, strong) WKSlug *slug;
@property (nonatomic, strong) WKCategory *category;

@end

@interface WKSlug : NSObject

@property (nonatomic, copy) NSString *value;

@end

With this model in place, we can create a simple test class to assert some behaviors.

Testing Path Patterns

Using a path pattern, we can generate URLs for resources, easily substituting tokens in the pattern
with values from keypaths on our objects.

- (void)testPathBuilding {
    WKWikiPage *page = [[WKWikiPage alloc] init];
    page.pageID = 15;
    page.slug = [[WKSlug alloc] init];
    page.slug.value = @"my-new-page";

    page.category = [[WKCategory alloc] init];
    page.category.name = @"RestKit";

    NSString *path = RKPathFromPatternWithObject(@"/wiki/:category.name/:pageID/:slug.value\\.html", page);
    NSLog(@"PATH: %@", path);

    STAssertEqualObjects(@"/wiki/RestKit/15/my-new-page.html", path, nil);
}

Here you can see that path segments are used as keypaths in the provided objects in order to
construct the desired URL.

Testing Routes

RKRoute is a class that uses Path Patterns in order to dynamically figure out what URL to
use for a given HTTP request.

For this test we'll need to provide a hook to allow for intercepting the actual HTTP requests
so they are not sent, but also to add assertions on the request sent.

@interface TestObjectManager : RKObjectManager
@property (nonatomic, strong) NSMutableArray *enqueuedOperations;
@end

@implementation TestObjectManager

- (void)enqueueObjectRequestOperation:(RKObjectRequestOperation *)objectRequestOperation {
    if (!self.enqueuedOperations) {
        self.enqueuedOperations = [NSMutableArray array];
    }

    [self.enqueuedOperations addObject:objectRequestOperation];
}

@end

Now that this is in place, we can use it instead of RKObjectManager when in our tests. The requests
will be caught by this method and never sent to super. We can now write our test:

- (void)testRouting {
    RKRoute *route = [RKRoute routeWithClass:[WKWikiPage class]
                                 pathPattern:@"pages/:pageID\\.json"
                                      method:RKRequestMethodAny];
    [self.objectManager.router.routeSet addRoute:route];

    WKWikiPage *page = [[WKWikiPage alloc] init];
    page.pageID = 15;

    [self.objectManager getObject:page
                             path:nil
                       parameters:nil
                          success:^(RKObjectRequestOperation *operation,
                                    RKMappingResult *mappingResult) {
                          } failure:^(RKObjectRequestOperation *operation,
                                      NSError *error) {
                          }];

    STAssertEquals(1, (int)self.objectManager.enqueuedOperations.count, nil);
    RKObjectRequestOperation *op = [self.objectManager.enqueuedOperations objectAtIndex:0];

    NSURL *url = op.HTTPRequestOperation.request.URL;
    NSString *urlString = [url description];
    STAssertEqualObjects(@"http://api.example.com/v2/pages/15.json", urlString, nil);
}

Testing Request Descriptors

RKRequestDescriptor can be added to an RKObjectManager to automatically convert an object
to it's desired representation for a request. For example if we wanted to create a new WKWikiPage
and save it on the server via an HTTP POST, we'd have to convert the page object
to a form-encoded or json structure for the request.

- (void)testRequestDescriptor {
    RKRoute *route = [RKRoute routeWithClass:[WKWikiPage class]
                                 pathPattern:@"pages/:pageID\\.json"
                                      method:RKRequestMethodAny];
    [self.objectManager.router.routeSet addRoute:route];

    WKWikiPage *page = [[WKWikiPage alloc] init];
    page.pageID = 15;
    page.slug = [[WKSlug alloc] init];
    page.slug.value = @"my-new-page";
    page.title = @"This is my new page";
    page.body = @"This is the body";

    page.category = [[WKCategory alloc] init];
    page.category.name = @"RestKit";

    RKObjectMapping *categoryRequestMapping = [RKObjectMapping requestMapping];
    [categoryRequestMapping addAttributeMappingsFromArray:@[@"name"]];

    RKObjectMapping *reqMapping = [RKObjectMapping requestMapping];
    [reqMapping addAttributeMappingsFromArray:@[@"title", @"body"]];
    [reqMapping addAttributeMappingsFromDictionary:@{@"slug.value": @"slug"}];
    [reqMapping addRelationshipMappingWithSourceKeyPath:@"category"
                                                mapping:categoryRequestMapping];

    RKRequestDescriptor *requestDescriptor = [RKRequestDescriptor requestDescriptorWithMapping:reqMapping
                                                                                   objectClass:[WKWikiPage class]
                                                                                   rootKeyPath:@"page"];
    [self.objectManager addRequestDescriptor:requestDescriptor];
    self.objectManager.requestSerializationMIMEType = RKMIMETypeJSON;
    [self.objectManager postObject:page
                              path:nil
                        parameters:nil
                           success:nil
                           failure:nil];

    STAssertEquals(1, (int)self.objectManager.enqueuedOperations.count, nil);
    RKObjectRequestOperation *op = [self.objectManager.enqueuedOperations objectAtIndex:0];
    NSData *data = op.HTTPRequestOperation.request.HTTPBody;
    NSString *json = [[NSString alloc] initWithData:data
                                           encoding:NSUTF8StringEncoding];
    NSLog(@"BODY: %@", json);
}

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