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我有一个名为 的实体Attribute，它有 2 个属性attribute_name和attribute_value.

这Attribute entity与另一个名为Project. 我想像所有一样插入它，attribute_name以使一个项目相同并且只是attribute_value不同。

当我输入数据时，我将这些属性用于两个不同数组中的实体，并使用循环Attribute将它们保存在继续单击按钮中。Savefor

为了保持attribute_name区别，我检查它们是否已经存在于数据库中，如果是，那么我只保存attribute_value. 但它仍然将“attributes_name”插入为NULL. 正在为 保存数据attributes_name。

因此，当我第二次单击“保存”按钮时，我得到的文本字段是以前的两倍。它们是空的。

NSFetchRequest * request = [[NSFetchRequest alloc] init];
    [request setEntity:[NSEntityDescription entityForName:@"Attributes" inManagedObjectContext:self.context]];
    [request setPredicate:[NSPredicate predicateWithFormat:@"attribute_name in %@", applicationDelegate.attributesTextArray]];
    NSError * error;
    NSArray * anArray = [context executeFetchRequest:request error:&error];

    for (int i = 0; i < [applicationDelegate.attributesTextArray count]; i++) {

        attributesObject = (Attributes*)[NSEntityDescription insertNewObjectForEntityForName:@"Attributes" inManagedObjectContext:self.context];
        if (anArray.count == 0) {
            attributesObject.attribute_name = [applicationDelegate.attributesTextArray objectAtIndex:i];
            attributesObject.attribute_value = [applicationDelegate.attributeGradesArray objectAtIndex:i];
        } else {
            attributesObject.attribute_value = [applicationDelegate.attributeGradesArray objectAtIndex:i];
        }

        [testArray addObject:attributesObject];
    } 
    for (int o=0; o<[testArray count]; o++) {

        NSData * retrievedData = [[NSUserDefaults standardUserDefaults] objectForKey:@"ProjectManagedObject"];
        NSURL * retrievedUrl = [NSKeyedUnarchiver unarchiveObjectWithData:retrievedData];
        NSManagedObjectID * projectObjectId = [applicationDelegate.persistentStoreCoordinator managedObjectIDForURIRepresentation:retrievedUrl];

        projectObject = (Project*)[applicationDelegate.managedObjectContext objectWithID:projectObjectId];
        [projectObject addAttributesObject:[testArray objectAtIndex:o]];
        NSError * error;
        if (![context save:&error]) {
            NSLog(@"UNABLE TO SAVE DATA: %@", [error userInfo]);
        }

这里到底出了什么问题？

更新：

NSFetchRequest * fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription * entity = [NSEntityDescription entityForName:@"Project" inManagedObjectContext:context];
    [fetchRequest setEntity:entity];
    NSError * error;
    NSArray * fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
    NSLog(@"OBJECT FETCHED:%d", [fetchedObjects count]);

    if (fetchedObjects.count != 0) {
        Project * project_ = [fetchedObjects objectAtIndex:applicationDelegate.projectNumber];
        NSArray * saved_attributes = [project_.attributes allObjects];
        if (saved_attributes.count != 0) {
             //Update "attribute-value"
} else {
             // create new attribute and insert both "attribute_name" and "attribute_value" ?
}
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1 回答 1

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你的线路

attributesObject = (Attributes*)[NSEntityDescription insertNewObjectForEntityForName:@"Attributes" inManagedObjectContext:self.context];

创建一个新的“属性”对象，与之前是否找到具有匹配名称的对象无关。如果要更新现有对象，则必须设置获取对象的属性，而不是创建新对象。

于 2013-08-07T07:49:14.707 回答