PATH Documentation > WebObjects 4.5 > EOControl Reference

EOKeyComparisonQualifier

Inherits from:
EOQualifier : NSObject

Conforms to:
EOQualifierEvaluation

EOQualifierSQLGeneration

Declared in:
EOControl/EOQualifier.h

Class Description

EOKeyComparisonQualifier is a subclass of EOQualifier that compares a named property of an object with a named value of another object. For example, to return all of the employees whose salaries are greater than those of their managers, you might use an expression such as "salary > manager.salary", where "salary" is the left key and "manager.salary" is the right key. The "left key" is the property of the first object that's being compared to a property in a second object; the property in the second object is the "right key." Both the left key and the right key might be key paths. You can use EOKeyComparisonQualifier to compare properties of two different objects or to compare two properties of the same object.

EOKeyComparisonQualifier adopts the EOQualifierEvaluation protocol, which defines the method evaluateWithObject: for in-memory evaluation. When an EOKeyComparisonQualifier object receives an evaluateWithObject: message, it evaluates the given object to determine if it satisfies the qualifier criteria.

In addition to performing in-memory filtering, EOKeyComparisonQualifier can be used to generate SQL. When it's used for this purpose, the key should be a valid property name of the root entity for the qualifier (or a valid key path).

Adopted Protocols

EOQualifierEvaluation
- evaluateWithObject:

EOQualifierSQLGeneration (EOAccess)
- sqlStringForSQLExpression:

- schemaBasedQualifierWithRootEntity:

Instance Methods

evaluateWithObject:

- (BOOL)evaluateWithObject:object

Returns YES if the object object satisfies the qualifier, NO otherwise. When an EOKeyComparisonQualifier object receives an evaluateWithObject: message, it evaluates object to determine if it meets the qualifier criteria. This method can raise one of several possible exceptions if an error occurs. If your application allows users to construct arbitrary qualifiers (such as through a user interface), you may want to write code to catch any exceptions and properly respond to errors (for example, by displaying a panel saying that the user typed a poorly formed qualifier).

initWithLeftKey:operatorSelector:rightKey:

- initWithLeftKey:(NSString *)leftKey operatorSelector:(SEL)selector rightKey:(NSString *)rightKey

Initializes the receiver to compare the properties named by leftKey and rightKey, using the operator selector selector, one of:

Enterprise Objects Framework supports SQL generation for these selectors only.

For example, the following excerpt creates an EOKeyComparisonQualifier qual that has the left key "lastName", the operator selector EOQualifierOperatorEqual, and the right key "member.lastName". Once constructed, the qualifier qual is used to filter an in-memory array. The code excerpt returns an array of Guest objects whose lastName properties have the same value as the lastName property of the guest's sponsoring member (this example is based on the Rentals sample database).

NSArray *guests;    /* Assume this exists. */
EOQualifier *qual = [[EOKeyComparisonQualifier alloc] 
    initWithLeftKey:@"lastName"
    operatorSelector:EOQualifierOperatorEqual
    rightKey:@"member.lastName"];

return [guests filteredArrayUsingQualifier:qual];