Inherits From:
Object (Java Client)
NSObject (Yellow Box)
Implements:
NSCoding (Java Client only)
Package:
com.apple.client.eocontrol (Java Client)
com.apple.yellow.eocontrol (Yellow Box)
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. EOFetchSpecification objects use an array of EOSortOrderings, which are applied in series to perform sorts by more than one property.
Sorting with SQL
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.
Defined Name |
SQL Expression |
---|---|
CompareAscending | (key) asc |
CompareDescending | (key) desc |
CompareCaseInsensitiveAscending | upper(key) asc |
CompareCaseInsensitiveDescending | upper(key) desc |
Using the mapping in the table above, the array of EOSortOrderings (nameOrdering ) created in the following code example:
EOSortOrdering lastNameOrdering =
EOSortOrdering.sortOrderingWithKey("lastName", EOSortOrdering.CompareAscending);
EOSortOrdering firstNameOrdering =
(EOSortOrdering.sortOrderingWithKey("firstName", EOSortOrdering.CompareAscending);
NSMutableArray nameOrdering = new NSMutableArray();
nameOrdering.addObject(lastNameOrdering);
nameOrdering.addObject(firstNameOrdering);
results in this ORDER BY clause:
order by (lastName) asc, (firstName) asc
In-Memory Sorting
The methods sortedArrayUsingKeyOrderArray and sortArrayUsingKeyOrderArray are used to sort objects in memory. Given an array of objects and an array of EOSortOrderings, sortedArrayUsingKeyOrderArray returns a new array of objects sorted according to the specified EOSortOrderings. Similarly, sortArrayUsingKeyOrderArray 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:
SortOrdering.sortVectorUsingKeyOrderVector(employees, nameOrdering);
Comparison Methods
The predefined comparison methods are:
The first two can be used with any value class; the second two with java.lang.String 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.
EOSortOrdering
public EOSortOrdering (java.lang.String key, NSSelector selector)
Creates and returns a new EOSortOrdering object. If key and selector are provided, the new EOSortOrdering is initialized with them.
See also: + sortOrderingWithKey
sortArrayUsingKeyOrderArray
public static void sortArrayUsingKeyOrderArray (NSMutableArray objects, NSArray sortOrderings)
Sorts objects in place according to the EOSortOrderings in sortOrderings. The objects are compared by extracting the sort properties using the EnterpriseObject method valueForKey and sending them compare... messages. See the table in "Sorting with SQL" for a list of the compare methods.
See also: + sortedArrayUsingKeyOrderArray
sortOrderingWithKey
public static EOSortOrdering sortOrderingWithKey (java.lang.String key, NSSelector selector)
Creates and returns an EOSortOrdering based on key and selector.
See also: "Constructors"
sortedArrayUsingKeyOrderArray
public static NSArray sortedArrayUsingKeyOrderArray (NSArray objects, NSArray sortOrderings)
Creates and returns a new array by sorting objects according to the SortOrderings in sortOrderings. The objects are compared by extracting the sort properties using the added NSObject method valueForKey and sending them compare... messages. See the table in "Sorting with SQL" for a list of the compare methods.
key
public java.lang.String key ()
Returns the key by which the receiver orders items.
See also: - selector
selector
public NSSelector selector ()
Returns the method selector used to compare values when sorting.
See also: - key