Question

我是Realm的新手，并且查询问题会让我疯狂几天。我有2个简单的类Dog和Person as：

class Dog: Object {
    dynamic var dogName = ""
    dynamic var dogAge = 1
    var owners: [Person] {
       return linkingObjects(Person.self, forProperty: "dogs")
    }
}

class Person: Object {
    dynamic var firstName = ""
    let dogs = List<Dog>()
}

向Realm添加数据后，我有以下数据：

奥斯卡有3只狗，分别是A，B和C，年龄分别为4,6和9
Jennifer有3只狗，分别是D，E和F，年龄分别为1,2和7
一只名叫Z的狗，8岁，没有主人。

的

let database = try! Realm()
// Query all Dogs- It should have 7 dogs
let allDogs = database.objects(Dog)
print("A total of \(allDogs.count) dogs")   // 7 dogs - correct

// Query All dogs between age of 4 and 12 - there should be 5 dogs

let agedDogs = database.objects(Dog).filter("dogAge BETWEEN {4,12}")
print("Dogs between Age 4 and 12 = \(agedDogs.count) \n")   // 5 dogs - OK

我想知道所有agedDog，其中有多少属于奥斯卡？我试过了：

let specificOwnerAgedDogs = agedDogs.filter("ANY owners.firstName = 'Oscar'")
print("Oscar Dogs between Age 4 and 12 = \(specificOwnerAgedDogs)")

但是此查询会导致错误：

由于未捕获的异常“无效的属性名称”而终止应用，原因：在“狗”类型的对象中找不到“属性”所有者

我正在使用Realm Swift和Swift 2.1.1。

Answer 1

Realm Swift does not yet support provide direct support for queries that traverse inverse relationships，例如owners类的Dog属性。这是我们正在努力的事情，它应该在不久的将来成为Realm Swift版本。

目前，您可以通过在Swift中执行某些过滤而不是在谓词中来解决此限制：

let specificOwners = database.objects(Person).filter("firstName = 'Oscar'")
let specificOwnerAgedDogs = specificOwners.flatMap() { owner in
    owner.dogs.filter() { $0.dogAge >= 4 && $0.dogAge <= 12 }
}

Answer 2

let noOwn = agedDogs.flatMap {
   (ndog) -> Dog? in
   ndog.owners == [] ? ndog : nil
}

我使用此代码查找没有任何所有者的所有oldDogs的列表？有没有想过这个？

查询反向关系

2 个答案: