RestKit/Code/CoreData/RKManagedObjectMappingOperationDataSource.m

//
//  RKManagedObjectMappingOperationDataSource.m
//  RestKit
//
//  Created by Blake Watters on 7/3/12.
//  Copyright (c) 2012 RestKit. All rights reserved.
//
//  Licensed under the Apache License, Version 2.0 (the "License");
//  you may not use this file except in compliance with the License.
//  You may obtain a copy of the License at
//
//  http://www.apache.org/licenses/LICENSE-2.0
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.
//

#import "RKManagedObjectMappingOperationDataSource.h"
#import "RKObjectMapping.h"
#import "RKEntityMapping.h"
#import "RKLog.h"
#import "RKManagedObjectStore.h"
#import "RKMappingOperation.h"
#import "RKDynamicMappingMatcher.h"
#import "RKManagedObjectCaching.h"
#import "RKRelationshipConnectionOperation.h"
#import "RKMappingErrors.h"

// Set Logging Component
#undef RKLogComponent
#define RKLogComponent RKlcl_cRestKitCoreData

extern NSString * const RKObjectMappingNestingAttributeKeyName;

@interface RKManagedObjectMappingOperationDataSource ()
@property (nonatomic, strong, readwrite) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, strong, readwrite) id<RKManagedObjectCaching> managedObjectCache;
@end

@implementation RKManagedObjectMappingOperationDataSource

- (id)initWithManagedObjectContext:(NSManagedObjectContext *)managedObjectContext cache:(id<RKManagedObjectCaching>)managedObjectCache
{
    NSParameterAssert(managedObjectContext);

    self = [self init];
    if (self) {
        self.managedObjectContext = managedObjectContext;
        self.managedObjectCache = managedObjectCache;
    }

    return self;
}

- (id)mappingOperation:(RKMappingOperation *)mappingOperation targetObjectForRepresentation:(NSDictionary *)representation withMapping:(RKObjectMapping *)mapping
{
    NSAssert(representation, @"Mappable data cannot be nil");
    NSAssert(self.managedObjectContext, @"%@ must be initialized with a managed object context.", [self class]);

    if (! [mapping isKindOfClass:[RKEntityMapping class]]) {
        return [mapping.objectClass new];
    }

    RKEntityMapping *entityMapping = (RKEntityMapping *)mapping;
    id object = nil;
    id primaryKeyValue = nil;
    NSString *primaryKeyAttribute;

    NSEntityDescription *entity = [entityMapping entity];
    RKAttributeMapping *primaryKeyAttributeMapping = nil;

    primaryKeyAttribute = [entityMapping primaryKeyAttribute];
    if (primaryKeyAttribute) {
        // If a primary key has been set on the object mapping, find the attribute mapping
        // so that we can extract any existing primary key from the mappable data
        for (RKAttributeMapping *attributeMapping in entityMapping.attributeMappings) {
            if ([attributeMapping.destinationKeyPath isEqualToString:primaryKeyAttribute]) {
                primaryKeyAttributeMapping = attributeMapping;
                break;
            }
        }

        // Get the primary key value out of the mappable data (if any)
        if ([primaryKeyAttributeMapping.sourceKeyPath isEqualToString:RKObjectMappingNestingAttributeKeyName]) {
            RKLogDebug(@"Detected use of nested dictionary key as primaryKey attribute...");
            primaryKeyValue = [[representation allKeys] lastObject];
        } else {
            NSString* keyPathForPrimaryKeyElement = primaryKeyAttributeMapping.sourceKeyPath;
            if (keyPathForPrimaryKeyElement) {
                primaryKeyValue = [representation valueForKeyPath:keyPathForPrimaryKeyElement];
            } else {
                RKLogWarning(@"Unable to find source attribute for primaryKeyAttribute '%@': unable to find existing object instances by primary key.", primaryKeyAttribute);
            }
        }
    }

    if (! self.managedObjectCache) {
        RKLogWarning(@"Performing managed object mapping with a nil managed object cache:\n"
                      "Unable to update existing object instances by primary key. Duplicate objects may be created.");
    }

    // If we have found the primary key attribute & value, try to find an existing instance to update
    if (primaryKeyAttribute && primaryKeyValue && NO == [primaryKeyValue isEqual:[NSNull null]]) {
        object = [self.managedObjectCache findInstanceOfEntity:entity
                                       withPrimaryKeyAttribute:primaryKeyAttribute
                                                         value:primaryKeyValue
                                        inManagedObjectContext:self.managedObjectContext];

        if (object && [self.managedObjectCache respondsToSelector:@selector(didFetchObject:)]) {
            [self.managedObjectCache didFetchObject:object];
        }
    }

    if (object == nil) {
        object = [[NSManagedObject alloc] initWithEntity:entity
                           insertIntoManagedObjectContext:self.managedObjectContext];
        if (primaryKeyAttribute && primaryKeyValue && ![primaryKeyValue isEqual:[NSNull null]]) {
            [object setValue:primaryKeyValue forKey:primaryKeyAttribute];
        }

        if ([self.managedObjectCache respondsToSelector:@selector(didCreateObject:)]) {
            [self.managedObjectCache didCreateObject:object];
        }
    }

    return object;
}

// Mapping operations should be executed against managed object contexts with the `NSPrivateQueueConcurrencyType` concurrency type
- (BOOL)executingConnectionOperationsWouldDeadlock
{
    return [NSThread isMainThread] && [self.managedObjectContext concurrencyType] == NSMainQueueConcurrencyType && self.operationQueue;
}

- (void)emitDeadlockWarningIfNecessary
{
    if ([self executingConnectionOperationsWouldDeadlock]) {
        RKLogWarning(@"Mapping operation was configured with a managedObjectContext with the `NSMainQueueConcurrencyType` concurrency type"
                      " and given an operationQueue to perform background work. This configuration will lead to a deadlock with"
                      " the main queue waiting on the mapping to complete and the operationQueue waiting for access to the MOC."
                      " You should instead provide a managedObjectContext with the NSPrivateQueueConcurrencyType.");
    }
}

- (BOOL)commitChangesForMappingOperation:(RKMappingOperation *)mappingOperation error:(NSError **)error
{
    if ([mappingOperation.objectMapping isKindOfClass:[RKEntityMapping class]]) {
        [self emitDeadlockWarningIfNecessary];
        
        NSArray *connectionMappings = [(RKEntityMapping *)mappingOperation.objectMapping connectionMappings];
        if ([connectionMappings count] > 0) {            
            NSDictionary *userInfo = @{ NSLocalizedDescriptionKey: @"Cannot map an entity mapping that contains connection mappings with a data source whose managed object cache is nil." };
            NSError *localError = [NSError errorWithDomain:RKErrorDomain code:RKMappingErrorNilManagedObjectCache userInfo:userInfo];
            if (error) *error = localError;
            return NO;
        }

        for (RKConnectionMapping *connectionMapping in connectionMappings) {
            RKRelationshipConnectionOperation *operation = [[RKRelationshipConnectionOperation alloc] initWithManagedObject:mappingOperation.destinationObject
                                                                                                          connectionMapping:connectionMapping
                                                                                                         managedObjectCache:self.managedObjectCache];
            [operation setCompletionBlock:^{
                if ([mappingOperation.delegate respondsToSelector:@selector(mappingOperation:didConnectRelationship:usingMapping:)]) {
                    [mappingOperation.delegate mappingOperation:mappingOperation didConnectRelationship:connectionMapping.relationship usingMapping:connectionMapping];
                }
            }];
            if (self.parentOperation) [operation addDependency:self.parentOperation];
            NSOperationQueue *operationQueue = self.operationQueue ?: [NSOperationQueue currentQueue];
            [operationQueue addOperation:operation];
            RKLogTrace(@"Enqueued %@ dependent upon parent operation %@ to operation queue %@", operation, self.parentOperation, operationQueue);
        }
    }
    
    return YES;
}

@end