ios - 核心数据过滤

Question

我有一个核心数据结构如下：

Business <-------->> Employee <-------->> Address

每个企业有多个员工，每个员工可以有多个地址。

从业务对象中，我希望能够获得指定特定条件的一个NSArray或NSSet所有对象。Address例如，所有街道名称都必须是唯一的。

我知道我可以覆盖，isEqual:但我猜这会产生意想不到的结果。否则，我一直在考虑使用valueForKeyPath:@"@distinctUnionOfObjects"，但我认为我不能通过条件。

这是我到目前为止的一些代码：

    NSMutableArray *addressArray = [NSMutableArray array];
    NSArray *employees = [Employee sortedArray];

    //loop through employees
    for (Employee *employee in employees) {
        for (Address *address in employee.addresses) {
            [addressArray addObject:address];
        }
    }

    //filter out duplicates
    addressArray = [addressArray valueForKeyPath:@"@distinctUnionOfObjects.city"];

这段代码给了我一个独特城市的列表，但是，我想要一个包含Address具有唯一city值（或其他条件）的对象的集合。

Answer 1

我找到了一种使用LinqToObjectiveC 库的方法：

NSArray* addressesWithUniqueCities = [input distinct:^id(id address) {
    return [address city];
}];

看源码，底层实现如下：

typedef id (^Selector)(id item);

-(NSArray *)distinct:(Selector)keySelector
{
    NSMutableSet* keyValues = [[NSMutableSet alloc] init];
    NSMutableArray* distinctSet = [[NSMutableArray alloc] init];
    for (id item in self) {
        id keyForItem = keySelector(item);
        if (![keyValues containsObject:keyForItem]) {
            [distinctSet addObject:item];
            [keyValues addObject:keyForItem];
        }
    }
    return distinctSet;
 }

我的最终代码最终是：

    NSMutableArray *addressArray = [NSMutableArray array];
    NSArray *employees = [Employee sortedEmployees];

    //loop through employees
    for (Employee *employee in employees) {
        for (Address *address in employee.addresses) {
            [addressArray addObject:address];
        }
    }

    //filter out duplicates
    NSArray *distinctAddressArray = [addressArray distinct:^id(id address) {
        return [address addressLine];
    }];

    return distinctAddressArray;

Answer 2

我不确定这是你的意思，但你可以尝试类似：（未经测试）

+ (NSMutableArray*) addressesForBusiness:(Business*)business
                         sectionProperty:(NSString*)sectionProperty
{

    NSFetchRequest* request = [[NSFetchRequest alloc] initWithEntityName:@"Address"];
    request.predicate = [NSPredicate predicateWithFormat:@"employee.business == %@",business.objectID];
    request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:sectionProperty ascending:YES]];

    NSArray* addresses = [business.managedObjectContext executeFetchRequest:request error:NULL];
    NSMutableArray* sections = [NSMutableArray new];
    NSMutableArray* currentSection = [NSMutableArray new];
    NSManagedObject* prevAddress = nil;
    for (NSManagedObject* address in addresses) {
        if (prevAddress && ([[address valueForKey:sectionProperty] isEqual:[prevAddress valueForKey:sectionProperty]])) {
            currentSection = [NSMutableArray new];
            [sections addObject:currentSection];
        }
        prevAddress = address;
        [currentSection addObject:address];
    }

    return sections;
}

这将返回一个数组数组，其中每个内部数组都保存具有相同属性值的对象。在您的示例中，您可以调用：

[[self class] addressesForBusiness:someBusiness sectionProperty:addressLine];