NSPredicate-谓词使用总结

简介

NSPredicate类主要用来指定过滤器的条件,该对象可以准确的描述所需条件，对每个对象通过谓词进行筛选，判断是否与条件相匹配。谓词是指在计算机中表示计算真假值的函数。原理和用法都类似于SQL查询中的where，作用相当于数据库的过滤取。主要用于从集合中分拣出符合条件的对象或者数据模型，也可以用于字符串的正则匹配.  
一般的, NSPredicate的筛选过滤的条件可以是, 逻辑运算符号(> , < , =),范围运算符(IN,BETWEEN),字符的包含/匹配/模糊搜索(BEGINSWITH,ENDSWITH,CONTAINS,LIKE), 正则表达式(MATCHES)等.

NSPredicate用法

1.谓词过滤筛选的过程

1.创建NSPredicate NSPredicate *predicate = [NSPredicate predicateWithFormat:@"过滤条件"];  2.判断指定的对象是否满足NSPredicate创建的过滤条件  [predicate evaluateWithObject:model];  3.将array通过创建的predicate进行过滤,并返回符合条件的数据  NSArray *resultArr = [array filteredArrayUsingPredicate:predicate]; 
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这些方法既适用于字符串这样的简单对象的过滤, 又适用于数据模型的过滤.

举例: 
对简单的字符串数组进行包含过滤

    NSArray *array=[@"abc",@"adbzc",@"adboc",@"skenabc",@"aksalkjjbc2c",@"111abc",@"a22bc4",@"abc4444",@"asdfad",@"alkmbc",@"abcopjoj",@"abjoc",@"khujabc",@"abc9074",];     NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF CONTAINS[cd] %@", @"abc"];    NSArray *resultArr = [array filteredArrayUsingPredicate:predicate];    NSLog(@"%@",resultArr);
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谓词过滤的筛选条件

1.逻辑运算符号(> , < , = , >= , <=) 
还可以跟逻辑运算符一起使用的: &&, || ,AND, OR 谓词不区分大小写

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"age > 20"];  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"height > 180 && age > 10"];  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"height > 180 OR age > 10"];
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2.范围运算符(IN,BETWEEN)

NSPredicate *predicate = [NSPredicate predicateWithFormat:"age BETWEEN {1,5}"];  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name IN {'abc' , 'def' , '123'}"];  
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3.字符串之开头和结尾(BEGINSWITH,ENDSWITH) 
BEGINSWITH:以**开头 
ENDSWITH:以**结尾

//name以N打头NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name BEGINSWITH 'N'"];  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name BEGINSWITH[c] 'M'"];  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name BEGINSWITH[d] 'C'"];  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name BEGINSWITH[cd] 'w'"];  
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注:字符串类的筛选条件中, [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。

4.字符串之包含和模糊查询(CONTAINS,LIKE) 
CONTAINS:包含某个字符串 
LIKE:模糊查询

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name CONTAINS 'N'"]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name LIKE '*N*'"];NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name LIKE[cd] '???er*"];
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注:LIKE中的?表示一个任意字符, *表示通配符

5.字符串匹配查询(SELF) 
以上说的都是对象中的属性匹配的筛选条件，如果数组中都是字符串,即非属性匹配查询, 需要用到SELF.

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF CONTAINS[cd] %@", @"abc"];
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6.正则表达式(MATCHES) 
NSPredicate 使用MATCHES 匹配正则表达式，正则表达式的写法采用international components 
for Unicode (ICU)的正则语法。 

NSString *regex = @"^A.+e$";//以A 开头，以e 结尾的字符。  NSPredicate *pre= [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regex];  
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举例

例一

NSArray *array=[NSArray arrayWithObjects:person1,person2,person3,person4,...,nil];  //方法一:手动过滤出age小于20的person数组NSPredicate *predicate = [NSPredicate predicateWithFormat:@"age < 20"];  for(Person *person in array){      if([predicate evaluateWithObject:person]){     //判断指定的对象是否满足    }  }  //方法二:直接获取过滤出age小于20的person数组NSArray *persons = [array filteredArrayUsingPredicate:predicate];//获取所有age小于20的person 
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例二

将self.dataSourceArray模型数组中, 对 groupname 和 diseasename两个分别进行筛选, 将筛选模型添加到self.resulArr中, 并去重.

    NSPredicate *namePredicate = [NSPredicate predicateWithFormat:@"groupname CONTAINS[cd] %@",searchString];    NSArray *nameArr = [self.dataSourceArray filteredArrayUsingPredicate:namePredicate];    NSPredicate *diseasePredicate = [NSPredicate predicateWithFormat:@"diseasemc CONTAINS[cd] %@",searchString];    NSArray *diseaseArr = [self.dataSourceArray filteredArrayUsingPredicate:diseasePredicate];    NSMutableSet *set = [NSMutableSet setWithArray:nameArr];    [set addObjectsFromArray:diseaseArr];    self.resultArr = [set sortedArrayUsingDescriptors:@[[[NSSortDescriptor alloc] initWithKey:@"groupname" ascending:YES]]];
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总结和注意

1.NSPredicate既适用于属性匹配,对数据模型或者dic进行过滤; 又适用于简单字符串的非属性匹配. 区别只是谓词的条件用法不同. 
2.在字符串筛选的谓词条件中, [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。 
3.在例子中, filteredArrayUsingPredicate语句是进行过滤的执行. 然后, 我们进入到NSPredicate类中, 可以发现, NSPredicateSupport对NSArray,NSMutableArray,NSSet,NSMutableSet,NSOrderedSet,NSMutableOrderedSet这些类都是适用的.

@interface NSArray<ObjectType> (NSPredicateSupport)- (NSArray<ObjectType> *)filteredArrayUsingPredicate:(NSPredicate *)predicate;    // evaluate a predicate against an array of objects and return a filtered array@end@interface NSMutableArray<ObjectType> (NSPredicateSupport)- (void)filterUsingPredicate:(NSPredicate *)predicate;    // evaluate a predicate against an array of objects and filter the mutable array directly@end@interface NSSet<ObjectType> (NSPredicateSupport)- (NSSet<ObjectType> *)filteredSetUsingPredicate:(NSPredicate *)predicate NS_AVAILABLE(10_5, 3_0);    // evaluate a predicate against a set of objects and return a filtered set@end@interface NSMutableSet<ObjectType> (NSPredicateSupport)- (void)filterUsingPredicate:(NSPredicate *)predicate NS_AVAILABLE(10_5, 3_0);    // evaluate a predicate against a set of objects and filter the mutable set directly@end@interface NSOrderedSet<ObjectType> (NSPredicateSupport)- (NSOrderedSet<ObjectType> *)filteredOrderedSetUsingPredicate:(NSPredicate *)p NS_AVAILABLE(10_7, 5_0);    // evaluate a predicate against an ordered set of objects and return a filtered ordered set@end@interface NSMutableOrderedSet<ObjectType> (NSPredicateSupport)- (void)filterUsingPredicate:(NSPredicate *)p NS_AVAILABLE(10_7, 5_0);  // evaluate a predicate against an ordered set of objects and filter the mutable ordered set directly@end
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