iOS 的 NSPredicate 使用方法

基本使用

格式化参数

查找name是 Asriel 且 money 等于 50 的 Person

let fetchRequest = NSFetchRequest<Person>(entityName: "Person")
fetchRequest.predicate = NSPredicate(format: "name == %@ AND money == %i", "Asriel", 50)

完整的格式化说明符可以看官方文档，下面列举几个常用的：

• %@ 用于字符串、日期、数组等
• %i 用于整数
• %f 用于浮点数
• %K 用于 Keypath，实体属性

let integerPredicate = NSPredicate(format: "money == %i", 10000)
let doublePredicate = NSPredicate(format: "perimeter > %f", 3.14159)
let stringPredicate = NSPredicate(format: "name == %@", "Asriel")

// 下面两个是一样的效果
let datePredicate = NSPredicate(format: "due_date < %@", Date())
let keyPathDatePredicate = NSPredicate(format: "%K < %@", "due_date", Date())

比较

基本的比较符号有：==，>，<，!= 等

let equalPredicate = NSPredicate(format: "name == %@", "Steve Jobs")
let notEqualPredicate = NSPredicate(format: "name != %@", "Steve Jobs")

let greaterPredicate = NSPredicate(format: "money > %i", 10000)
let greaterOrEqualPredicate = NSPredicate(format: "money >= %i", 10000)

let lesserPredicate = NSPredicate(format: "money < %i", 10000)
let lesserOrEqualPredicate = NSPredicate(format: "money <= %i", 10000)

复合比较：OR，AND

// 匹配所有条件
let andPredicate = NSPredicate(format: "name == %@ AND money >= %i", "Steve Jobs", 10000)

// 匹配条件之一
let orPredicate = NSPredicate(format: "name == %@ OR money >= %i", "Steve Jobs", 10000)

不区分大小写比较：在比较符号后面加[c]

// 匹配 "jobs", "Jobs", "jObS"
let caseInsensitivePredicate = NSPredicate(format: "name ==[c] %@", "Jobs")

高级技巧

使用替换变量来重用 NSPredicate

使用$来表示变量，通过方法withSubstitutionVariables来替换变量，参数是字典类型。

// Persons' name : ["Asriel", "Asgore", "Toriel", "Frisk", "Flowey"]
let context = appDelegate.persistentContainer.viewContext
let fetchRequest = NSFetchRequest<Person>(entityName: "Person")

let reusablePredicate = NSPredicate(format: "name BEGINSWITH $startingName")

// 替换 $startingName 为 'As'
fetchRequest.predicate = reusablePredicate.withSubstitutionVariables(["startingName" : "As"])

do {
  people = try context.fetch(fetchRequest)
  // ["Asriel", "Asgore"]
} catch let error as NSError {
  print("Could not fetch. \(error), \(error.userInfo)")
}

// 再次重用reusablePredicate
// 替换 $startingName 为 'F'
fetchRequest.predicate = reusablePredicate.withSubstitutionVariables(["startingName" : "F"])

do {
  people += try context.fetch(fetchRequest)
  // ["Asriel", "Asgore", "Flowey", "Frisk"]
} catch let error as NSError {
  print("Could not fetch. \(error), \(error.userInfo)")
}

可以使用多个替换变量，比如name BEGINSWITH $startingName AND money > $amount，然后调用withSubstitutionVariables(["startingName" : "As", "amount": 50])

过滤数组对象

SELF 在格式化字符串里面表示数组里面的 每个元素。

let names = ["Kim Kardashian", "Kim Jong Un", "Jimmy Kimmel", "Ken"]

var filteredNames : [String] = []

// SELF 表示数组的每个元素
let containPredicate = NSPredicate(format: "SELF CONTAINS %@", "Kim")

filteredNames = names.filter({ name in
    // 如果元素满足条件，返回true，否则返回false
	containPredicate.evaluate(with: name)
})

print("\(filteredNames)")
// ["Kim Kardashian", "Kim Jong Un", "Jimmy Kimmel"]

例子

是否包含在数组里

let wantedItemIDs = [1, 2, 3, 5, 8, 13, 21]

// 获取在wantedItemIDs里面的记录
let inclusivePredicate = NSPredicate(format: "item_id IN %@", wantedItemIDs)

是否不包含在数组里

let unwantedItemIDs = [1, 2, 3, 5, 8, 13, 21]

// 获取不在wantedItemIDs里面的记录
let exclusivePredicate = NSPredicate(format: "NOT (item_id IN %@)", unwantedItemIDs)

是否以特定字符串开头

// Works for "Kim Jong Un", "Kim Kardashian"
let beginPredicate = NSPredicate(format: "name BEGINSWITH %@", "Kim")

// Works for "macintosh", "Macintosh"
let beginCaseInsensitivePredicate = NSPredicate(format: "name BEGINSWITH[c] %@", "mac")
// the [c] means case insensitive match

是否包含特定字符串

// Works for "Steven Paul Jobs", "Logan Paul"
let containPredicate = NSPredicate(format: "name CONTAINS %@", "Paul")

// Works for "Shop1", "shopping", "my shop", "bishop"
let containCaseInsensitivePredicate = NSPredicate(format: "name CONTAINS[c] %@", "shop")
// the [c] means case insensitive match

是否以特定字符串结束

// Works for "Steve Jobs", "Lisa Jobs"
let endPredicate = NSPredicate(format: "name ENDSWITH %@", "Jobs")

// Works for "mundane jobs", "Steve Jobs"
let endCaseInsensitivePredicate = NSPredicate(format: "name ENDSWITH[c] %@", "jobs")
// the [c] means case insensitive match

通配符

LIKE 用于通配符匹配，下面介绍匹配字符代表的意思：

• * 代表 0 个或者多个字符
• ? 代表 1 个字符

let filenameArr = ["img.png", "img1.png", "img2.png", "img10.png", "img100.png", "img200.txt", "img300.csv"]

let pngPredicate = NSPredicate(format: "SELF LIKE %@", "img*.png")

let imageArr = filenameArr.filter(){ filename in
	pngPredicate.evaluate(with: filename)
}
print(imageArr)
// ["img.png", "img1.png", "img2.png", "img10.png", "img100.png"]


let singleCharPngPredicate = NSPredicate(format: "SELF LIKE %@", "img?.png")

let imageArr2 = filenameArr.filter(){ filename in
	singleCharPngPredicate.evaluate(with: filename)
}
print(imageArr2)
// ["img1.png", "img2.png"]

正则表达式匹配

MATCHES 用于正则表达式

filename MATCHES 'img\\d{1,3}\\.png' 会匹配到在img和.png之间包含 1 到 3 个 数字的文件名，但不包括img1000.png。注意反斜杠需要加转义字符\。

let filenameArr = ["img.png", "img1.png", "imgABC.png", "img10.png", "img100.png", "img9000.png", "img12345.png"]

// matches filename that has 1-3 digits between 'img' and '.png'
let regexPredicate = NSPredicate(format: "SELF MATCHES %@", "img\\d{1,3}\\.png")

let filteredArr = filenameArr.filter(){ filename in
    regexPredicate.evaluate(with: filename)
}
print(filteredArr)
// ["img1.png", "img10.png", "img100.png"]