EOSortOrdering

Inherits from:

NSObject

Conforms to:

NSCoding

NSObject (NSObject)

Declared in:

EOControl/EOSortOrdering.h

Class Description

An EOSortOrdering object specifies the way that a group of objects should be sorted, using a property key and a method selector for comparing values of that property. EOSortOrderings are used both to generate SQL when fetching rows from a database server, and to sort objects in memory. Both the EOFetchSpecification class and the added NSArray sorting methods accept an array of EOSortOrderings, which are applied in series to perform sorts by more than one property.

When an EOSortOrdering is used to fetch data from a relational database, it's rendered into an ORDER BY clause for a SQL SELECT statement according to the concrete adaptor you're using. For more information, see the class description for EOSQLExpression. The Framework predefines symbols for four comparison selectors, listed in the table below. The table also shows an example of how the comparison selectors can be mapped to SQL.

Using the mapping in the table above, the array of EOSortOrderings (nameOrdering) created in the following code example:

NSArray *nameOrdering = [NSArray arrayWithObjects:
    [EOSortOrdering sortOrderingWithKey:@"lastName" selector:EOCompareAscending],
    [EOSortOrdering sortOrderingWithKey:@"firstName" selector:EOCompareAscending],
    nil];

results in this ORDER BY clause:

order by (lastName) asc, (firstName) asc

In-Memory Sorting

Enterprise Objects Framework adds a method each to NSArray and NSMutableArray for sorting objects in memory. NSArray's sortedArrayUsingKeyOrderArray: returns a new array of objects sorted according to the specified EOSortOrderings. Similarly, NSMutableArray's sortUsingKeyOrderArray: sorts the provided array of objects in place. This code fragment, for example, sorts an array of Employee objects in place, by last name, then first name using the array of EOSortOrderings created above:

NSArray *sortedEmployees = [employees sortedArrayUsingKeyOrderArray:nameOrdering];

Constants

In EOSortOrdering.h, EOControl defines the following selector constants:

The first two can be used with any value class; the second two with NSString objects only. The sorting methods extract property values using key-value coding and apply the selectors to the values. If you use custom value classes, you should be sure to implement the appropriate comparison methods to avoid exceptions when sorting objects.

Adopted Protocols

NSCoding

- encodeWithCoder:

- initWithCoder:

Method Types

Creating instances

- initWithKey:selector:

Examining a sort ordering

- key

- selector

Class Methods

sortOrderingWithKey:selector:

+ (EOSortOrdering *)sortOrderingWithKey:(NSString *)key selector:(SEL)selector

See Also: - initWithKey:selector:

Instance Methods

initWithKey:selector:

- (id)initWithKey:(NSString *)key selector:(SEL)aSelector

See Also: + EOSortOrdering

key

- (NSString *)key

See Also: - selector

selector

- (SEL)selector

See Also: - key