StackOverflow2013

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POCore Data, One-To-Many Relationship
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copied!<p>I new to iOS development and doing some test with the core data. It was all fine until I started playing with relationship. In context:</p> <p>I have 2 entity: Article and Category.</p> <p>Article has two members idArticle and text. Articles has to have a single Category. Category has two members idCategory and name. Category can have 0 or several Articles.</p> <p>Article:</p> <ul> <li>idArticle</li> <li>text</li> <li>category (Relationship to Category, Inverse = articles, minimum optional, maximum 1)</li> </ul> <p>Category:</p> <ul> <li>idCategory</li> <li>name</li> <li>articles (To many Relationship to Article, Inverse = category, minimum optional, maximum unlimited)</li> </ul> <p>While I am adding an article. I am first surprise to not only have article1.category but also article1.idCategory and article1.name! I have currently set all my attributes, relationship to optional. Whatever I do, when I add a new article using the code below, it will add a new Category as well which will contain idCategory = 0 and name = nil if I dont set article.idCategory and article.name! or to the corresponding value if I set them. However, I don't want it to create that category, I just want to add an existing category. article.category works fine; it add the article to the right category! If I only set article.category; article.idCategory will = 0 and article.name = nil.</p> <p>I suppose that I could delete the newly created category but I want my code to be neat. I have search the web but didnt find similar example with that problem. I am not dealing with any GUI here. My code:</p> <pre><code> - (BOOL)createNewGmtArticle:(NSNumber*)articleID title:(NSString*)paramTitle text:(NSString*)paramText date:(NSDate*)paramDate categoryID:(NSNumber*)paramCategoryID categoryName:(NSString*)paramCategoryName { GasMattersTodayArticles *gmtArticle = [NSEntityDescription insertNewObjectForEntityForName:@"GasMattersTodayArticles" inManagedObjectContext:self.managedObjectContext]; // Look the given entitiy GasMattersTodayArticles in the given managed obj context if(gmtArticle != nil) { // Fill article gmtArticle.idArticle = articleID; gmtArticle.text = paramText; gmtArticle.category = [self getGmtCategoryWithId:paramCategoryID]; //gmtArticle.idCategory = gmtArticle.category.idCategory; //gmtArticle.name = gmtArticle.category.name; NSError *savingError = nil; if([self.managedObjectContext save:&savingError]) // flush all unsaved data of the context to the persistent store { NSLog(@"Successfully saved the context"); return YES; } else { NSLog(@"Failed to save the context. Error = %@", savingError); return NO; } } NSLog(@"Failed to create the new article"); return NO; } </code></pre> <p>and</p> <pre><code>-(GasMattersTodayCategory *)getGmtCategoryWithId:(NSNumber*)categoryID { // Create the fetch request first NSDictionary *subs = [NSDictionary dictionaryWithObject:categoryID forKey:@"SEARCH_KEY"]; NSFetchRequest *fetchRequest = [self.managedObjectModel fetchRequestFromTemplateWithName:@"CategoryWithKey" substitutionVariables:subs]; // Entity whose contents we want to read NSEntityDescription *entity = [NSEntityDescription entityForName:@"GasMattersTodayCategory" inManagedObjectContext:self.managedObjectContext]; // Tell the request that we want to read the content of the person entity [fetchRequest setEntity:entity]; // Excecute the fetch request on the context NSError* requestError = nil; GasMattersTodayCategory *category = [[self.managedObjectContext executeFetchRequest:fetchRequest error:&requestError] lastObject]; // Make sur we get a category if(category != nil) { return category; } else { NSLog(@"Could not find any Category entities with this Id in the context."); return nil; } } </code></pre> <p>Thanks! This super basic task is currently ruining my sunday!</p>

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