Realm 允许您按排序顺序接收查询结果。
let realm = try! Realm()
let dogs = realm.objects(Dog.self)
let dogsSorted = dogs.sorted(byKeyPath: "name", ascending: false)
我运行了这个测试来看看领域返回排序数据的速度有多快
import Foundation
import RealmSwift
class TestModel: Object {
@Persisted(indexed: true) var value: Int = 0
}
class RealmSortTest {
let documentCount = 1000000
var smallestValue: TestModel = TestModel()
func writeData() {
let realm = try! Realm()
var documents: [TestModel] = []
for _ in 0 ... documentCount {
let newDoc = TestModel()
newDoc.value = Int.random(in: 0 ... Int.max)
documents.append(newDoc)
}
try! realm.write {
realm.deleteAll()
realm.add(documents)
}
}
func readData() {
let realm = try! Realm()
let sortedResults = realm.objects(TestModel.self).sorted(byKeyPath: "value")
let start = Date()
self.smallestValue = sortedResults[0]
let end = Date()
let delta = end.timeIntervalSinceReferenceDate - start.timeIntervalSinceReferenceDate
print("Time Taken: \(delta)")
}
func updateSmallestValue() {
let realm = try! Realm()
let sortedResults = realm.objects(TestModel.self).sorted(byKeyPath: "value")
smallestValue = sortedResults[0]
print("Originally loaded smallest value: \(smallestValue.value)")
let newSmallestValue = TestModel()
newSmallestValue.value = smallestValue.value - 1
try! realm.write {
realm.add(newSmallestValue)
}
print("Originally loaded smallest value after write: \(smallestValue.value)")
let readStart = Date()
smallestValue = sortedResults[0]
let readEnd = Date()
let readDelta = readEnd.timeIntervalSinceReferenceDate - readStart.timeIntervalSinceReferenceDate
print("Reloaded smallest value \(smallestValue.value)")
print("Time Taken to reload the smallest value: \(readDelta)")
}
}
使用documentCount = 100000, readData() 输出：
Time taken to load smallest value: 0.48901796340942383
和 updateData() 输出：
Originally loaded smallest value: 2075613243102
Originally loaded smallest value after write: 2075613243102
Reloaded smallest value 2075613243101
Time taken to reload the smallest value: 0.4624580144882202
使用documentCount = 1000000, readData() 输出：
Time taken to load smallest value: 4.807577967643738
和 updateData() 输出：
Originally loaded smallest value: 4004790407680
Originally loaded smallest value after write: 4004790407680
Reloaded smallest value 4004790407679
Time taken to reload the smallest value: 5.2308430671691895
从排序的结果集中检索第一个文档所花费的时间随着存储在领域中的文档数量而不是正在检索的文档数量而缩放。这向我表明，领域是在查询时而不是在编写文档时对所有文档进行排序。有没有一种方法可以索引您的数据，以便您可以快速检索少量排序的文档？
编辑：
在评论中的讨论之后，我更新了代码以仅加载排序集合中的最小值。
编辑 2
我observe按照评论中的建议将代码更新为结果。
import Foundation
import RealmSwift
class TestModel: Object {
@Persisted(indexed: true) var value: Int = 0
}
class RealmSortTest {
let documentCount = 1000000
var smallestValue: TestModel = TestModel()
var storedResults: Results<TestModel> = (try! Realm()).objects(TestModel.self).sorted(byKeyPath: "value")
var resultsToken: NotificationToken? = nil
func writeData() {
let realm = try! Realm()
var documents: [TestModel] = []
for _ in 0 ... documentCount {
let newDoc = TestModel()
newDoc.value = Int.random(in: 0 ... Int.max)
documents.append(newDoc)
}
try! realm.write {
realm.deleteAll()
realm.add(documents)
}
}
func observeData() {
let realm = try! Realm()
print("Loading Data")
let startTime = Date()
self.storedResults = realm.objects(TestModel.self).sorted(byKeyPath: "value")
self.resultsToken = self.storedResults.observe { changes in
let observationTime = Date().timeIntervalSince(startTime)
print("Time to first observation: \(observationTime)")
let firstTenElementsSlice = self.storedResults[0..<10]
let elementsArray = Array(firstTenElementsSlice) //print this if you want to see the elements
elementsArray.forEach { print($0.value) }
let moreElapsed = Date().timeIntervalSince(startTime)
print("Time to printed elements: \(moreElapsed)")
}
}
}
我得到以下输出
Loading Data
Time to first observation: 5.252112984657288
3792614823099
56006949537408
Time to printed elements: 5.253015995025635
用观察者读取数据并没有减少读取数据的时间。