realm cocoa: predicate to select items not related

问题

in a model like this:

class Order : RLMObject {
    dynamic var orderId = ""
    // ... other fields
}

class Product: RLMObject {
    dynamic var productId = ""
    dynamic var productName = ""
}

// This class relates products to orders, so an order may have multiple products and
// a product may appear in multiple orders
class OrderedProduct : RLMObject {
    dynamic var order: Order
    dynamic var product: Product
    dynamic var quantity: 1
}

Question: How do I select all products that are not part of an order?

here's how I am doing it right now:

let order = //... an order object user selected in the interface
let allOrderedProducts = OrderedProduct.objectsWhere("order.orderId  == %@", order.orderId)
var productIds = Array<String()
for op in allOrderedProducts {
    let orderedProduct = op as OrderedProduct
    productIds.append(orderedProduct.product.productId)
}

let allProductsNotInOrder = Product.objectsWhere("NOT (productId IN %@)", productIds)

It works, but I am not happy with it, is there a way to fetch allProductsNotInOrder in one db access.

Thanks.

来源：https://stackoverflow.com/questions/27728575/realm-cocoa-predicate-to-select-items-not-related

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