NSPredicate and nspredicate

NSPredicate and nspredicate

Cocoa provides a class named NSPredicate, which is used to specify filter conditions and describe the query method using NSPredicate. The principle is similar to querying in a database. The NSPredicate class can be used in database-style APIs, commonly used for Core Data and Spotlight. This article describes how to use a certain category, such as garage (garage class) and car (car), for example only. The creation code is not listed. Understanding the usage of predicate is the key.

Create Predicate.

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name == 'Herbie'"];

Calculate Predicate

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"engine.horsepowe > 150"];    NSArray *cars = [garage cars];    for (Car *car in [garage cars]) {        if ([predicate evaluateWithObject:car]) {            NSLog(@"%@",car.name);        }    }

Traverse the array to retrieve objects that meet the conditions.

Array Filter

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"engine.horsepowe > 150"];    NSArray *results;    results = [cars filteredArrayUsingPredicate:predicate];

Suppose you have a variable array and you need to remove all items that do not belong to the array. Use the following methods:

    NSMutableArray *carsCopy = [cars mutableCopy];    [carsCopy filterUsingPredicate:predicate];

Flexible Predicate construction

There are two ways,

First format specifier

    NSPredicate *predicate1, *predicate2, *predicate3;        predicate1 = [NSPredicate predicateWithFormat:@"engine.horsepowe > %d",50];        predicate2 = [NSPredicate predicateWithFormat:@"name == %@",@"Herbie"];        predicate3 = [NSPredicate predicateWithFormat:@"%k == %@", @"name", @"Herbie"];

The second method is to put the variable name in a string, which is similar to the environment variable.

This predicate is equivalent to predicate3 and predicate2 in the first one.

    NSPredicate *predicateTemplate = [NSPredicate predicateWithFormat:@"name == $NAME"];        NSDictionary *varDict;    varDict = [NSDictionary dictionaryWithObjectsAndKeys:@"Herbie",@"NAME", nil];        NSPredicate *predicate = [predicateTemplate predicateWithSubstitutionVariables:varDict];

This predicate is equivalent to predicate1 in the first one.

    predicateTemplate = [NSPredicate predicateWithFormat:@"engine.horsepower > $POWER"];        varDict = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:150], @"POWER", nil];        predicate = [predicateTemplate predicateWithSubstitutionVariables:varDict];

Predicate Operator

Common operators supporting C language ==><>=! = <>& |! AND OR NOT

    predicate = [NSPredicate predicateWithFormat:@"(engine.horsepower > 50) AND (engine.horsepower < 200)"];    results = [cars filteredArrayUsingPredicate:predicate];

Array Operators

    predicate = [NSPredicate predicateWithFormat:@"engine.horsepower BETWEEN{50,200}"];

Equivalent

    NSArray *betweens = [NSArray arrayWithObjects:[NSNumber numberWithInt:50],[NSNumber numberWithInt:200],nil];    predicate = [NSPredicate predicateWithFormat:@"engine.horsepower BEWEEN %@",betweens];

SELF keyword response predicate calculation object

    NSArray *names1 = [NSArray arrayWithObjects:@"Herbie",@"Badger",@"Judge",@"Elvis", nil];    NSArray *names2 = [NSArray arrayWithObjects:@"Judge",@"Paper Car",@"Badger",@"Phoenix", nil];        predicate = [NSPredicate predicateWithFormat:@"SELF IN %@", names1];    results = [names2 filteredArrayUsingPredicate:predicate];    NSLog(@"%@", results);

The answer is:

(
Judge,

Badger

)

String Operators

BEGINSWITH check whether a string starts with another string

ENDSWITH checks whether a string ends with another string

CONTAINS checks whether a string is inside another string
For example, if "name BEGINSWITH 'bad'" is used to match a Badger, It is case sensitive. If it matches a BADGer, it cannot match.
To ignore the rules such as uppercase and lowercase letters and heavy notes, you can add [cd] "name BEGINSWITH [cd] 'herb'" to match Herbie. Generally, it is better to add [cd ].

LIKE Operator
"Name LIKE '* er *'" will match any name containing er, equivalent to CONTAINS "name LIKE '??? Er * '"will match Paper Car but will not match Badger. er is limited to three characters. If you are keen on regular expressions, you can use the MATCHES operator, assign it a regular expression.

Reprinted please indicate the original:Http://blog.csdn.net/marvindev