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EOQualifier


Inherits from:
NSObject
Conforms to:
NSCopying
Declared in:
EOControl/EOQualifier.h



Class Description

EOQualifier is an abstract class for objects that hold information used to restrict selections on objects or database rows according to specified criteria. With the exception of EOSQLQualifier (EOAccess), qualifiers aren't based on SQL and they don't rely upon an EOModel (EOAccess). Thus, the same qualifier can be used both to perform in-memory searches and to fetch from the database.

You never instantiate an instance of EOQualifier. Rather, you use one of its subclasses-one of the following or your own custom EOQualifier subclass:


Subclass Purpose
EOKeyValueQualifier Compares the named property of an object to a supplied value, for example, "weight > 150".
EOKeyComparisonQualifier Compares the named property of one object with the named property of another, for example "name = wife.name".
EOAndQualifier Contains multiple qualifiers, which it conjoins. For example, "name = 'Fred' AND age < 20".
EOOrQualifier Contains multiple qualifiers, which it disjoins. For example, "name = 'Fred' OR name = 'Ethel'".
EONotQualifier Contains a single qualifier, which it negates. For example, "NOT (name = 'Fred')".
EOSQLQualifier Contains unstructured text that can be transformed into a SQL expression. EOSQLQualifier provides a way to create SQL expressions with any arbitrary SQL. Because EOSQLQualifiers can't be evaluated against objects in memory and because they contain database and SQL-specific content, you should use EOQualifier wherever possible.

The protocol EOQualifierEvaluation defines how qualifiers are evaluated in memory. To evaluate qualifiers in a database, methods in EOSQLExpression (EOAccess) and EOEntity (EOAccess) are used to generate SQL for qualifiers. Note that all of the SQL generation functionality is contained in the access layer.

For more information on using EOQualifiers, see the sections




Constants

In EOQualifier.h, EOControl defines the following selector constants to represent the qualifier operators:


EOQualifierOperatorEqual EOQualifierOperatorGreaterThanOrEqualTo
EOQualifierOperatorNotEqual EOQualifierOperatorContains
EOQualifierOperatorLessThan EOQualifierOperatorLike
EOQualifierOperatorGreaterThan EOQualifierOperatorCaseInsensitiveLike
EOQualifierOperatorLessThanOrEqualTo  



Adopted Protocols

NSCopying


Method Types

Creating a qualifier
+ qualifierWithQualifierFormat:
+ stringForOperatorSelector:
+ qualifierToMatchAllValues:
+ qualifierToMatchAnyValue:
- qualifierWithBindings:requiresAllVariables:
In-memory filtering
- evaluateWithObject:
Converting strings and operators
+ operatorSelectorForString:
+ stringForOperatorSelector:
Get EOQualifier operators
+ allQualifierOperators
+ relationalQualifierOperators
Accessing a qualifiers keys
- allQualifierKeys
- addQualifierKeysToSet:
Accessing a qualifier's binding keys
- bindingKeys
- keyPathForBindingKey:
Validating a qualifier's keys
- validateKeysWithRootClassDescription:


Class Methods


allQualifierOperators

+ (NSArray *)allQualifierOperators

Returns an NSArray containing all of the operators supported by EOQualifier: =, !=, <, <=, >, >=, "like", and "caseInsensitiveLike".

See Also: + relationalQualifierOperators


operatorSelectorForString:

+ (SEL)operatorSelectorForString:(NSString *)aString

Returns an operator selector based on the string aString. This method is used in parsing a qualifier. For example, the following statement returns the selector isNotEqualTo:.
selector = [EOQualifier operatorSelectorForString:@"!="];

The possible values of aString are =, ==, !=, <, >, <=, >=, "like", and "caseInsensitiveLike".

You'd probably only use this method if you were writing your own qualifier parser.

See Also: + stringForOperatorSelector:


qualifierToMatchAllValues:

+ (EOQualifier *)qualifierToMatchAllValues:(NSDictionary *)values

Takes a dictionary of search criteria, from which the method creates EOKeyValueQualifiers (one for each dictionary entry). The method ANDs these qualifiers together, and returns the resulting EOAndQualifier.

qualifierToMatchAnyValue:

+ (EOQualifier *)qualifierToMatchAnyValue:(NSDictionary *)values

Takes a dictionary of search criteria, from which the method creates EOKeyValueQualifiers (one for each dictionary entry). The method ORs these qualifiers together, and returns the resulting EOOrQualifier.

qualifierWithQualifierFormat:

+ (EOQualifier *)qualifierWithQualifierFormat:(NSString *)qualifierFormat, ...

Parses the format string qualifierFormat, uses it to create an EOQualifier, and returns the EOQualifier.

Based on the content of qualifierFormat, this method generates a tree of the basic qualifier types. For example, the format string "firstName = 'Joe' AND department = 'Facilities'" generates an EOAndQualifier that contains two "sub" EOKeyValueQualifiers. The following code excerpt shows a typical way to use the qualifierWithQualifierFormat: method. The excerpt constructs an EOFetchSpecification, which includes an entity name and a qualifier. It then applies the EOFetchSpecification to the EODisplayGroup's data source and tells the EODisplayGroup to fetch.

EODisplayGroup *displayGroup;     /* Assume this exists.*/
EOFetchSpecification *fetchSpec;
EODatabaseDataSource *dataSource;
    
dataSource = [displayGroup dataSource];    
fetchSpec = [EOFetchSpecification 
    fetchSpecificationWithEntityName:@"Member"
    qualifier:[EOQualifier qualifierWithQualifierFormat:
            @"cardType = 'Visa' "]
    sortOrderings:nil];    
[dataSource setFetchSpecification:fetchSpec];
[displayGroup fetch];

qualifierWithQualifierFormat performs no verification to ensure that keys referred to by the format string qualifierFormat exist. It raises an NSInvalidArgumentException if qualifierFormat contains any syntax errors.


qualifierWithQualifierFormat:arguments:

+ (EOQualifier *)qualifierWithQualifierFormat:(NSString *)qualifierFormat arguments:(NSArray *)arguments

Parses the format string qualifierFormat and the specified arguments, uses them to create an EOQualifier, and returns the EOQualifier. This method is equivalent to qualifierWithQualifierFormat: except that format characters (for example, %@, %d, %f) in qualifierFormat cause the method to search in the arguments array for values rather than in a variable argument list. Note that although %d and %f can be used when constructing qualifiers, they don't work with most other string formatting methods such as NSString's stringWithFormat:.

qualifierWithQualifierFormat:varargList:

+ (EOQualifier *)qualifierWithQualifierFormat:(NSString *)format varargList:(va_list)args

Parses the format string qualifierFormat and the corresponding arguments in args, uses the arguments to create an EOQualifier, and returns the EOQualifier. This method is equivalent to qualifierWithQualifierFormat:.

relationalQualifierOperators

+ (NSArray *)relationalQualifierOperators

Returns an NSArray containing all of the relational operators supported by EOQualifier: =, !=, <, <=, >, and >=. In other words, returns all of the EOQualifier operators except for the ones that work exclusively on strings: "like" and "caseInsensitiveLike".

See Also: + allQualifierOperators


stringForOperatorSelector:

+ (NSString *)stringForOperatorSelector:(SEL)aSelector

Returns a string representation of the selector aSelector. For example, the following statement returns the string "!=":
operator = [EOQualifier stringForOperatorSelector:EOQualifierOperatorNotEqual];

The possible values for selector are as follows:

You'd probably use this method only if you were writing your own parser.

See Also: + operatorSelectorForString:



Instance Methods


addQualifierKeysToSet:

- (void)addQualifierKeysToSet:(NSMutableSet *)qualKeys

Adds the receiver's qualifier keys to qualKeys. The subclasses in the EOControl framework do this by traversing the tree of qualifiers. Node qualifiers (such as EOAndQualifier) recursively invoke this method until they reach a leaf qualifier (such as EOKeyValueQualifier) which adds its key to the set.

Subclasses of EOQualifier must implement this method.


allQualifierKeys

- (NSSet *)allQualifierKeys

Returns an NSSet of strings, which are the left-hand sides of all the qualifiers in the receiver. For example, if you have a qualifier

salary > 10000 AND manager.lastName = 'smith'

allQualifierKeys returns an array containing the strings "salary" and "manager.lastName".

Subclasses should not override this method, instead they should override addQualifierKeysToSet:.


bindingKeys

- (NSArray *)bindingKeys

Returns an array of strings which are the names of the known variables. Multiple occurrences of the same variable will only appear once in this list.

evaluateWithObject:

- (BOOL)evaluateWithObject:(id)object

Implemented by subclasses to return YES if object matches the criteria specified in the receiver, NO otherwise. The argument, object, should be an enterprise object, a snapshot dictionary, or something that implements key-value coding.

keyPathForBindingKey:

- (NSString *)keyPathForBindingKey:(NSString *)key

Returns a string which is the "left-hand-side" of the variable in the qualifier. e.g. If you have a qualifier "salary > $amount and manager.lastName = $manager", then calling bindingKeys would return the array ("amount", "manager"). Calling keyPathForBindingKey would return salary for amount, and manager.lastname for manager.

qualifierWithBindings:requiresAllVariables:

- (EOQualifier *)qualifierWithBindings:(NSDictionary *)bindings requiresAllVariables:(BOOL)requiresAll

Returns a new qualifier substituting all variables with values found in bindings. If requiresAll is YES, any variable not found in bindings raises an EOQualifierVariableSubstitutionException. If requiresAll is NO, missing variable values cause the qualifier node to be pruned from the tree.

validateKeysWithRootClassDescription:

- (NSException *)validateKeysWithRootClassDescription:(EOClassDescription *)classDesc

Ensures that the receiver contains keys and key paths that belong to or originate from classDesc. This method returns an NSInternalInconsistencyException if an unknown key is found, otherwise it returns nil to indicate that the keys contained by the qualifier are valid.


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