NSPredicate谓词查询

1、谓词：在计算机语言的环境下，谓词是指条件表达式的求值返回真或假的过程。 Cocoa框架中的NSPredicate用于查询，原理和用法都类似于SQL中的where，作用相当于数据库的过滤器。 根据条件查询name = 德玛 NSString *sqlString = select * from Student where name = 德玛; sqlite3_prepare(db, sqlString.UTF8String, -1, &stmt, NULL) 在没有用这个类时，我们要获取两个数组中某些特定的元素时，需要写代码一一对比，但是使用了这个类，只需要三四行代码就够了。 在iOS开发中，系

2、统提供了NSPredicate这个类给我们进行一些匹配、筛选操作，非常方便。创建了6个学生,并初始化,存放到数组中 Student *stu1 = Student studentWithName:li age:8 gender:nan; Student *stu2 = Student studentWithName:li age:10 gender:nv; Student *stu3 = Student studentWithName:wang age:12 gender:nan; Student *stu4 = Student studentWithName:wang age:14 gend

3、er:nan; Student *stu5 = Student studentWithName:zhang age:16 gender:nv; Student *stu6 = Student studentWithName:zhang age:18 gender:nan; Student *stu7 = Student studentWithName:zhao age:20 gender:nv; Student *stu8 = Student studentWithName:zhao age:22 gender:nan; Student *stu9 = Student studentWithN

4、ame:sun age:24 gender:nv; Student *stu10 = Student studentWithName:sun age:26 gender:nan; NSArray *studentAry = stu1,stu2,stu3,stu4,stu5,stu6,stu7,stu8,stu9,stu10; 在不使用NSPredicate这个类的时候,要获取数组中学生姓名是li的人,我们这样做 NSMutableArray *liAry = NSMutableArray array; for (Student *student in studentAry) if (stude

5、 isEqualToString:li) liAry addObject:student; NSLog(姓名是li%,liAry); 在不使用NSPredicate这个类的时候,要获取数组中学生姓名以z开头的人,我们这样做 NSMutableArray *zAry = NSMutableArray array; for (Student *student in studentAry) NSString *name = ; NSString *firstLetter = name substringToIndex:1; if (firstLetter isE

6、qualToString:z) zAry addObject:student; NSLog(姓名以z开头%,zAry); 在不使用NSPredicate这个类的时候,要获取数组中学生姓名以g结尾的人,我们这样做 NSMutableArray *gAry = NSMutableArray array; for (Student *student in studentAry) NSString *name = ; NSString *lastLetter = name substringFromIndex:name.length - 1; if (lastLetter is

7、EqualToString:i) gAry addObject:student; NSLog(姓名以g结尾%,gAry); 在不使用NSPredicate这个类的时候,要获取数组中学生姓名包含a的人,我们这样做 NSMutableArray *aAry = NSMutableArray array; for (Student *student in studentAry) NSString *name = ; for (int i = 0; i (int)name.length; i+) NSString *letter = name substringWithRang

8、e:NSMakeRange(i, 1); if (letter isEqualToString:a) aAry addObject:student; NSLog(%,aAry); 在不使用NSPredicate这个类的时候,要获取数组中学生姓名包含an的人,我们这样做 NSMutableArray *anAry = NSMutableArray array; for (Student *student in studentAry) NSString *name = ; for (int i = 0; i (int)name.length - 1; i+) NSStrin

9、g *nowLetter = name substringWithRange:NSMakeRange(i, 1); NSString *nextLetter = name substringWithRange:NSMakeRange(i + 1, 1); if (nowLetter isEqualToString:a & nextLetter isEqualToString:n) anAry addObject:student; NSLog(%,anAry); 使用NSPredicate,可以替我们省去很多代码 NSPredicate继承自NSObeject, 创建一个谓词语句 + (NSPr

10、edicate *)predicateWithFormat:(NSString *)predicateFormat, .; 回顾以前的知识 + (instancetype)sortDescriptorWithKey:(nullable NSString *)key ascending:(BOOL)ascending NS_AVAILABLE(10_6, 4_0); - (NSArray *)sortedArrayUsingDescriptors:(NSArray *)sortDescriptors; - (void)sortUsingDescriptors:(NSArray *)sortDes

11、criptors; - (NSArray *)sortedArrayUsingSelector:(SEL)comparator; - (void)sortUsingSelector:(SEL)comparator; 谓词语句的执行对象是集合的时候 interface NSArray (NSPredicateSupport) - (NSArray *)filteredArrayUsingPredicate:(NSPredicate *)predicate; end interface NSMutableArray (NSPredicateSupport) - (void)filterUsingP

12、redicate:(NSPredicate *)predicate; end 谓词语句的执行对象是对象的时候 - (BOOL)evaluateWithObject:(nullable id)object; / evaluate a predicate against a single object 和字符串相关的 NSPredicate *predicate2 = NSPredicate predicateWithFormat: CONTAINS %,li; NSLog(姓名中包含li字符串%,studentAry filteredArrayUsingPredicate:pr

13、edicate2); NSPredicate *predicate3 = NSPredicate predicateWithFormat:name BEGINSWITH %,z; NSLog(姓名以小写z开头%,studentAry filteredArrayUsingPredicate:predicate3); NSPredicate *predicate4 = NSPredicate predicateWithFormat:name ENDSWITH %,g; NSLog(姓名以小写g结尾%,studentAry filteredArrayUsingPredicate:predicate4

14、); NSPredicate *predicate5 = NSPredicate predicateWithFormat: = %,li; NSLog(姓名等于字符串li%,studentAry filteredArrayUsingPredicate:predicate5); 注:c不区分大小写 d不区分发音符号即没有重音符号 cd既不区分大小写，也不区分发音符号。 范围运算符 BETWEEN ,IN NSPredicate *predicate6 = NSPredicate predicateWithFormat:age BETWEEN18,30; NSLog(%,stud

15、entAry filteredArrayUsingPredicate:predicate6); NSPredicate *predicate7 = NSPredicate predicateWithFormat:age IN18,30,25; NSLog(%,studentAry filteredArrayUsingPredicate:predicate7); 比较运算符 = = != NSPredicate *predicate8 = NSPredicate predicateWithFormat:age %d,20; NSLog(%,studentAry filteredArrayUsin

16、gPredicate:predicate8); NSPredicate *predicate9 = NSPredicate predicateWithFormat:age = %d,20; NSLog(%,studentAry filteredArrayUsingPredicate:predicate9); 逻辑运算符 | & ! NSPredicate *preciate10 = NSPredicate predicateWithFormat:age %d,10,20; NSLog(年龄小于15岁或者大于20岁的%,studentAry filteredArrayUsingPredicate

17、:preciate10); NSPredicate *preciate11 = NSPredicate predicateWithFormat:name BEGINSWITH % & age %d,z,20; NSLog(年龄小于15岁或者大于20岁的%,studentAry filteredArrayUsingPredicate:preciate11); NSPredicate *preciate12 = NSPredicate predicateWithFormat:age != %d,20; NSLog(年龄小于15岁或者大于20岁的%,studentAry filteredArrayU

18、singPredicate:preciate12); 通配符 *代表通配符是任意个任意字符的意思,?代表一个任意字符 (like 像,如同的意思) NSPredicate *predicate10 = NSPredicate predicateWithFormat:name like *h*; NSLog(%,studentAry filteredArrayUsingPredicate:predicate10); NSPredicate *predicate11 = NSPredicate predicateWithFormat:name like ?n*; NSLog(%,studentAr

19、y filteredArrayUsingPredicate:predicate11); 正则表达式 z|g 代表一个字符,z或者g z 代表以z开头 g$ 代表以g结尾 z* 代表z可以出现零次或多次,和0, z+ 代表z可以出现一次或多次,和1, z? 代表z可以出现零次或一次,和z0,1等价 zn 代表z出现n次 zn, 代表z出现至少n次 zn,m 代表z出现至少n次,最多m次 . 代表除n以外的任何单个字符 xyz 代表xyz中个任意一个字符 xyz 代表除了xyz三个字符外的任意字符 a-z 代表小写a到z之间任意字符 0-9 代表小写0到9之间任意字符 A-Z 代表小写A到Z之间任

20、意字符 a-z 代表除a到z之间任意字符 要是仅仅想使用限定符作为一个字符,而不是作为限定符来使用就在前面加 正则表达式 MATCHES /NSString *regex = z.g$; NSString *regex = a-z+; NSPredicate *predicate12 = NSPredicate predicateWithFormat: MATCHES %,regex; NSLog(%,studentAry filteredArrayUsingPredicate:predicate12); 如果数组中存放的是字符串 NSArray *ary1 = 12,456789,123789,123963; NSPredicate *predicate1 = NSPredicate predicateWithFormat:self CONTAINS %,123; NSLog(%,ary1 filteredArrayUsingPredicate:predicate1); NSPredicate *predicate111 = NSPredicate predicateWithFormat:self.length = %d,2; NSLog(%,ary1 filteredArrayUsingPredicate:pre