Creating Sort Orderings

Synopsis

Describes how to create EOSortOrderings used either to specify fetch order or to sort an array in memory.

Discussion

An array of EOSortOrderings is used within EOF to specify the sort order for a fetch, as well as to specify a sort order to sort an array of enterprise objects already in memory. An EOSortOrdering consists of a key, for example, lastName , and a sort direction, for example, caseInsensitiveAscending . For database fetches, the key can be either an attribute of the object or an attribute path such as studio.name . When sorting an array in memory, the key can be any key that the object can respond to via valueForKey or valueForKeyPath . This allows you to sort on values returned from methods of the object. For example, you can sort on a derived attribute like fullName , even though it is a method.

Creating an array of EOSortOrdering objects defines a complete sort specification. Since a sort ordering is completely generic, it can be used with EOFetchSpecifications and in-memory filters.

Sorting During Fetches

An EOFetchSpecification object can be given an array of EOSortOrderings to be applied during the fetch. It is the database adaptor's responsibility to use the array of sort orderings and return rows in the specified sorted order. The standard relational database adaptors included with EOF convert the array of EOSortOrdering objects into a SQL ORDER BY clause.

The following example fetches all movies that have a title starting with "S", and requests the database to sort them first by the category (case-insensitive ascending) and then by the title (case-insensitive descending).

Creating a sort ordering (Java)

 
public WOComponent fetch() {    EOEditingContext ec=session().defaultEditingContext();    EOQualifier qual=EOQualifier.qualifierWithQualifierFormat         ("title like 'S*'", null);    Object orderings[]={        EOSortOrdering.sortOrderingWithKey("category",             EOSortOrdering.CompareCaseInsensitiveAscending),        EOSortOrdering.sortOrderingWithKey("title",             EOSortOrdering.CompareCaseInsensitiveDescending)};    EOFetchSpecification fs=new EOFetchSpecification        ("Movie", qual, new NSArray(orderings));    movies=ec.objectsWithFetchSpecification(fs);    return null;}

Note
WebScript does not know about the names describing sort direction, since they are defined using #define in EOSortOrdering.h . Since WebScript will convert a string object into an Objective-C selector when necessary, uncomment the definitions for sort direction when using WebScript.

Creating a sort ordering (Objective-C and WebScript)

 
- fetch {    /* Uncomment these definitions for WebScript    id EOCompareAscending=@"compareAscending:";    id EOCompareDescending=@"compareDescending:";    id EOCompareCaseInsensitiveAscending=@"compareCaseInsensitiveAscending:";    id EOCompareCaseInsensitiveDescending=        @"compareCaseInsensitiveDescending:";    */    EOEditingContext *ec=[[self session] defaultEditingContext];    EOQualifier *qual=[EOQualifier qualifierWithQualifierFormat:        @"title like 'S*'"];    NSArray *orderings=[NSArray arrayWithObjects:        [EOSortOrdering sortOrderingWithKey:@"category"              selector: EOCompareCaseInsensitiveAscending],        [EOSortOrdering sortOrderingWithKey:@"title"             selector: EOCompareCaseInsensitiveDescending], nil];    EOFetchSpecification *fs=[EOFetchSpecification         fetchSpecificationWithEntityName: @"Movie"        qualifier: qual sortOrderings: orderings];    movies =[ec objectsWithFetchSpecification: fs];    return nil;}

SQL log

 
[<ODBCChannel: 0xae0f70> evaluateExpression: <ODBCSQLExpression: "SELECT  t0.`CATEGORY`, t0.`DATE_RELEASED`, t0.`LANGUAGE`, t0.`MOVIE_ID`, t0.`POSTER_NAME`, t0.`REVENUE`, t0.`STUDIO_ID`, t0.`TITLE`, t0.`TRAILER_NAME` FROM `MOVIE` t0  WHERE t0.`TITLE` like ? ORDER BY UCASE(t0.`CATEGORY`) asc, UCASE(t0.`TITLE`) desc" withBindings:(1:S%(title))>]

 
Object orderings[]={ 
    EOSortOrdering.sortOrderingWithKey("category",  
        EOSortOrdering.CompareCaseInsensitiveAscending), 
    EOSortOrdering.sortOrderingWithKey("title", 
        EOSortOrdering.CompareCaseInsensitiveDescending)}; 
 
// This returns a new array in sorted order. 
NSArray newSortedArray=sortedArrayUsingKeyOrderArray 
    (originalArray, new NSArray(orderings)); 
 
// This resorts the mutableArray itself. 
sortArrayUsingKeyOrderArray 
    (originalMutableArray, new NSArray(orderings));

 
/* Uncomment these definitions for WebScript 
id EOCompareAscending=@"compareAscending:"; 
id EOCompareDescending=@"compareDescending:"; 
id EOCompareCaseInsensitiveAscending=@"compareCaseInsensitiveAscending:"; 
id EOCompareCaseInsensitiveDescending=@"compareCaseInsensitiveDescending:"; 
*/ 
 
NSArray *orderings=[NSArray arrayWithObjects: 
    [EOSortOrdering sortOrderingWithKey:@"category" 
        selector: EOCompareCaseInsensitiveAscending], 
    [EOSortOrdering sortOrderingWithKey:@"title" 
        selector: EOCompareCaseInsensitiveDescending], nil]; 
 
// This returns a new array in sorted order. 
NSArray *newSortedArray=[originalArray  
    sortedArrayUsingKeyOrderArray: orderings]; 
 
// This resorts the mutableArray itself. 
[originalMutableArray  sortUsingKeyOrderArray: orderings];

See Also

• Fetching with an Editing Context
• Creating Fetch Specifications Programmatically
• Creating EOQualifiers Programmatically
• EOSortOrdering class specification in the Enterprise Objects Framework Reference
• EOFetchSpecification class specification in the Enterprise Objects Framework Reference
• EOEditingContext class specification in the Enterprise Objects Framework Reference

Questions

• How do I fetch records in sorted order?
• What is the EOF equivalent of the SQL ORDER BY clause?
• How do I sort an array in memory?
• How do I get case-insensitive sort to work with MSAccess?

Keywords

• Sort
• ORDER BY
• EOSortOrdering
• UPPER
• UCASE

Revision History

21 July, 1998. David Scheck. First Draft.
19 November 1998. Clif Liu. Second Draft.