TWTValidation is a Cocoa framework for declaratively validating data. It provides a mechanism for validating individual objects and collections, and for combining multiple validators using logical operators to create more complex validations.

What’s New in 1.1

TWTValidation 1.1 adds several new validators and updates existing validators to be more flexible.

Additions

• TWTValueSetValidator validates that a value is in a set of valid values.
• TWTPrefixStringValidator ensures that a string has a given prefix.
• TWTSuffixStringValidator ensures that a string has a given suffix.
• TWTSubstringStringValidator validates that a string contains a particular substring.
• TWTWildcardPatternStringValidator validates that a string matches a wildcard pattern. Wildcard patterns support the use of the * and ? wildcard characters.
• TWTCharacterSetStringValidator validates that a string only contains characters in a given character set.

Updates

• TWTCollectionValidator checks that values respond to -count and conform to the NSFastEnumeration protocol before attempting to validate the value. Previously, if value did not meet those criteria, a crash would occur inside -validateValue:error:.
• Similarly, TWTKeyedCollectionValidator checks that values respond to -count and -objectForKey: and conform to the NSFastEnumeration protocol before attempting to validate the value.
• TWTNumberValidator now allows for exclusive minimum and maximum values, which validate that a value is strictly greater than a minimum or strictly less than a maximum, respectively.
• TWTKeyValueCodingValidator now attempts to get a key’s validators using -twt_validatorsForKey: before using +twt_validatorsForKey. This enables dynamic validators based on an instance’s state. See the class documentation for more information.
• All validation errors now include the failing validator in the error’s userInfo dictionary. This can be retrieved using -[NSError twt_failingValidator].

Features

• Simple, well-documented, and well-tested Objective-C API
• Flexible system for validating objects that makes few assumptions about your model classes
• Strong error reporting to help you understand which validators failed and why
• Built-in validators for validating numbers and strings
• Block validators to easily create validators with custom logic
• Compound validators that combine validators using logical operations like AND, OR, and NOT.
• Collection validators to validate a collection’s count and elements
• Keyed collection validators to validate a keyed collection’s count, keys, values, and specific key-value pairs
• Key-Value Coding validators to validate an object’s keys and values using validators defined by the object’s class
• An easy-to-extend API for creating your own reusable validators
• Works with both iOS and OS X

Installation

The easiest way to start using TWTValidation is to install it with CocoaPods.

pod 'TWTValidation', '~> 1.1'

You can also build it and include the built products in your project. For OS X, just add TWTValidation.framework to your project. For iOS, add TWTValidation’s public headers to your header search path and link in libTWTValidation.a, all of which can be found in the project’s build output directory.

Using TWTValidation

TWTValidation provides validators for a variety of use cases, but doesn’t constrain how you use them. All validators in TWTValidation inherit from TWTValidator, an abstract class that declares the primary interface to a validator, ‑validateValue:error:. This method validates the specified value and returns whether it passed validation. If the value failed to validate, an error describing why validation failed is returned indirectly via the error parameter.

Let’s step through each of the major subclasses of TWTValidator in turn. These are merely summaries of what’s possible. For more detailed information, check out the documentation in each class’s header.

Value Validators

Value validators inherit from TWTValueValidator. By itself, TWTValueValidator can only perform some basic validations: it can optionally ensure that a value is an instance of a specific class, not nil, and not the NSNull instance.

TWTValueValidator *validator = [TWTValueValidator valueValidatorWithClass:[NSNumber class]     
                                                                allowsNil:NO 
                                                               allowsNull:YES];

NSError *error = nil;
[validator validateValue:@10 error:&error];             // Returns YES
[validator validateValue:[NSNull null] error:&error];   // Returns YES
[validator validateValue:@"foo" error:&error];          // Returns NO
[validator validateValue:nil error:&error];             // Returns NO

More useful validations are performed by TWTValueValidator’s subclasses, TWTStringValidator and TWTNumberValidator. String validators can validate that a value is a string and has a given prefix or suffix; contains a given substring; matches a specified wildcard pattern or regular expression; or has a length within a specified range:

NSRegularExpression *regEx = [[NSRegularExpression alloc] initWithPattern:@"^[A-Z][a-z]+$"
                                                                  options:0
                                                                    error:NULL];

NSError *error = nil;
TWTStringValidator *validator = [TWTStringValidator stringValidatorWithRegularExpression:regEx 
                                                                                 options:0];
[validator validateValue:@"Uppercase" error:&error];    // Returns YES
[validator validateValue:@"lowercase" error:&error];    // Returns NO

validator = [TWTStringValidator stringValidatorWithMinimumLength:4 maximumLength:10];
[validator validateValue:@"Foobar" error:&error];       // Returns YES
[validator validateValue:@"Foo" error:&error];          // Returns NO

validator = [TWTStringValidator stringValidatorWithPrefix:@"foob" caseSensitive:NO];
[validator validateValue:@"Foobar" error:&error];       // Returns YES
[validator validateValue:@"Foo" error:&error];          // Returns NO

validator = [TWTStringValidator stringValidatorWithSuffix:@"oo" caseSensitive:YES];
[validator validateValue:@"Foobar" error:&error];       // Returns NO
[validator validateValue:@"Foo" error:&error];          // Returns YES

validator = [TWTStringValidator stringValidatorWithSubstring:@"OBA" caseSensitive:NO];
[validator validateValue:@"Foobar" error:&error];       // Returns YES
[validator validateValue:@"Foo" error:&error];          // Returns NO

validator = [TWTStringValidator stringValidatorWithPattern:@"*b*" caseSensitive:YES];
[validator validateValue:@"Foobar" error:&error];        // Returns YES
[validator validateValue:@"Foo" error:&error];           // Returns NO

validator = [TWTStringValidator stringValidatorWithCharacterSet:[NSCharacterSet letterCharacterSet]];
[validator validateValue:@"Foobar" error:&error];       // Returns YES
[validator validateValue:@":)" error:&error];           // Returns NO

Number validators ensure that a number is within a specified range and optionally has no fractional part.

TWTNumberValidator *validator = [[TWTNumberValidator alloc] initWithMinimum:@10 maximum:@20];

NSError *error = nil;
[validator validateValue:@15.333 error:&error];         // Returns YES
[validator validateValue:@3 error:&error];              // Returns NO

validator.exclusiveMinimum = YES;
[validator validateValue:@10 error:&error];              // Returns NO

validator.requiresIntegralValue = YES;
[validator validateValue:@15.333 error:&error];         // Returns NO

Compound Validators

Instances of TWTCompoundValidator, or simply compound validators, allow you to combine validators using logical operations like AND, OR, and NOT.

TWTNumberValidator *rangeValidator = [TWTNumberValidator numberValidatorWithMinimum:@2 maximum:@10];
TWTCompoundValidator *notValidator = [TWTCompoundValidator notValidatorWithSubvalidator:rangeValidator];

NSError *error = nil;
[notValidator validateValue:@3 error:&error];           // Returns NO
[notValidator validateValue:@0.123 error:&error];       // Returns YES
[notValidator validateValue:@"foo" error:&error];       // Returns YES, :-(

TWTNumberValidator *numberValidator = [[TWTNumberValidator alloc] init];
NSArray *subvalidators = @[ numberValidator, notValidator ];
TWTCompoundValidator *andValidator = [TWTCompoundValidator andValidatorWithSubvalidators:subvalidators];

[andValidator validateValue:@3 error:&error];           // Returns NO
[andValidator validateValue:@0.123 error:&error];       // Returns YES
[andValidator validateValue:@"foo" error:&error];       // Returns NO, :-)

TWTNumberValidator *integralValidator = [rangeValidator copy];
integralValidator.requiresIntegralValue = YES;
subvalidators = @[ andValidator, integralValidator ];
TWTCompoundValidator *orValidator = [TWTCompoundValidator orValidatorWithSubvalidators:subvalidators];

[orValidator validateValue:@3 error:&error];            // Returns YES
[orValidator validateValue:@7.33 error:&error];         // Returns NO
[orValidator validateValue:@0 error:&error];            // Returns YES
[orValidator validateValue:@"foo" error:&error];        // Returns NO

Block Validators

TWTBlockValidators allow you to specify a block to perform arbitrary validations.

TWTBlockValidator *validator = [[TWTBlockValidator alloc] initWithBlock:^BOOL(id value, NSError **error) {
    BOOL validated = [value isKindOfClass:[NSNumber class]] && value.integerValue % 2 == 0;
    if (!validated && error) {
        *error = [NSError twt_validationErrorWithCode:5 
                                                value:value 
                                 localizedDescription:NSLocalizedString(@"Value is not in set", nil)];
    }

    return validated;
}];

NSError *error = nil;
[validator validateValue:@"value1" error:&error];       // Returns YES
[validator validateValue:@"value4" error:&error];       // Returns NO

Collection Validators

You can validate a collection’s count and elements using an instance of TWTCollectionValidator. Collection validators use fast enumeration to get a collection’s elements. As such, it is primarily intended for validating arrays, sets, and ordered sets. However, it can work with any object that implements NSFastEnumeration and responds to ‑count.

TWTNumberValidator *countValidator = [[TWTNumberValidator alloc] initWithMinimum:@1 maximum:@3];

NSRegularExpression *regEx = [[NSRegularExpression alloc] initWithPattern:@"^[A-Z][a-z]+$"
                                                                  options:0
                                                                    error:NULL];
NSArray *elementValidators = @[ [TWTStringValidator stringValidatorWithRegularExpression:regEx 
                                                                                 options:0] ];

TWTCollectionValidator *validator = 
        [[TWTCollectionValidator alloc] initWithCountValidator:countValidator
                                             elementValidators:elementValidators];

NSError *error = nil;
id collection = [NSSet setWithObjects:@"Apple", @"Pear", @"Orange", nil];
[validator validateValue:collection error:&error];      // Returns YES

collection = @[ @"Apple", @"Pear", @"orange" ];
[validator validateValue:collection error:&error];      // Returns NO

collection = [NSOrderedSet orderedSetWithObjects:@"Apple", @"Pear", @"Orange", @"Grape", nil];
[validator validateValue:collection error:&error];      // Returns NO

Keyed Collection Validators

To validate dictionaries and map tables, use TWTKeyedCollectionValidators. These validator can validate a keyed collection’s count, keys, and values, as well as specific key-value pairs.

TWTNumberValidator *countValidator = [[TWTNumberValidator alloc] initWithMinimum:@1 maximum:@3];
TWTStringValidator *keyValidator = [[TWTStringValidator alloc] init];
TWTStringValidator *valueValidator = [[TWTNumberValidator alloc] init];

TWTNumberValidator *ageValidator = [[TWTNumberValidator alloc] initWithMinimum:@0 maximum:@130];
TWTKeyValuePairValidator *agePairValidator = [[TWTKeyValuePairValidator alloc] initWithKey:@"age"
                                                                            valueValidator:ageValidator]

TWTKeyedCollectionValidator *validator = 
        [[TWTKeyedCollectionValidator alloc] initWithCountValidator:countValidator
                                                      keyValidators:@[ keyValidator ]
                                                    valueValidators:@[ valueValidator ]
                                             keyValuePairValidators:@[ agePairValidator ]];

NSError *error = nil;
id collection = @{ @"key1" : @1 };
[validator validateValue:collection error:&error];      // Returns YES

collection = @{ @"key1" : @1, @"key2" : @2, @"key3" : @3, @"key4" : @4 };
[validator validateValue:collection error:&error];      // Returns NO

collection = @{ @1 : @2 };
[validator validateValue:collection error:&error];      // Returns NO

collection = @{ @"key1" : @"value1" };
[validator validateValue:collection error:&error];      // Returns NO

collection = @{ @"key1" : @1, @"key2" : @2, @"age" : @11 };
[validator validateValue:collection error:&error];      // Returns YES

collection = @{ @"key1" : @1, @"key2" : @2, @"age" : @-3 };
[validator validateValue:collection error:&error];      // Returns NO

Key-Value Coding Validators

Perhaps the most interesting and useful validators in TWTValidation are key-value coding validators. These objects—instances of TWTKeyValueCodingValidator—validate an object’s values for a given set of key-value coding compliant keys. It gets the validators to use for each key from the object’s class, in much the same way that key-value observing gets the key paths affecting a key. This is best explained using an example:

// Header File
@interface TWTSimplePerson : NSObject

@property (nonatomic, copy) NSString *firstName;
@property (nonatomic, copy) NSString *lastName;
@property (nonatomic, strong) NSNumber *age;

- (BOOL)isValid;

@end


// Implementation File
#import <TWTValidation/TWTValidation.h>

@interface TWTSimplePerson ()
@property (nonatomic, strong) TWTKeyValueCodingValidator *validator;
@end


@implementation TWTSimplePerson

- (instancetype)init
{
    self = [super init];
    if (self) {
        NSSet *keys = [NSSet setWithObjects:@"firstName", @"lastName", @"age", nil];
        _validator = [[TWTKeyValueCodingValidator alloc] initWithKeys:keys];
    }

    return self;
}


- (BOOL)isValid
{
    return [self.validator validateValue:self error:NULL];
}


// Key-value coding validators get the validators for their KVC keys by invoking -twt_validatorsForKey:
// and +twt_validatorsForKey: on the value’s class. The base implementations of those methods simply check
// to see if the class implements -twt_validatorsFor«Key» and +twt_validatorsFor«Key», where «Key» is the
// capitalized form of the KVC key. When you have multiple keys that use the same validators, you can override
// this implementation. Here, we return the same validators for firstName and lastName, but rely on the 
// superclass implementation to invoke -twt_validatorsForAge to get the validators for the age key.

+ (NSSet *)twt_validatorsForKey:(NSString *)key
{
    if ([key isEqualToString:@"firstName"] || [key isEqualToString:@"lastName"]) {
        return [NSSet setWithObject:[TWTStringValidator stringValidatorWithMinimumLength:1 maximumLength:20]];        
    } 

    return [super twt_validatorsForKey:key];
}


- (NSSet *)twt_validatorsForAge
{
    return [NSSet setWithObject:[[TWTNumberValidator alloc] initWithMinimum:@0 maximum:@130]];
}

@end

For a more detailed example of how to use key-value coding validators, see our example project.

Creating Custom Validators

If one of TWTValidation’s validators doesn’t meet your needs, it’s easy to add new validators or extend existing ones. Simply subclass TWTValidator or one of its subclasses and override ‑validateValue:error:. Take a look at any TWTValidator subclass for more guidance. We also provide some convenience methods for building error objects, which can be found in TWTValidationErrors.h.

Contributing, Filing Bugs, and Requesting Enhancements

If you would like to help fix bugs or add features to TWTValidation, send us a pull request!

We use GitHub issues for bugs, enhancement requests, and the limited support we provide, so open an issue for any of those.

License

All code is licensed under the MIT license. Do with it as you will.