Fetching with an Editing Context
Discussion
Instead of using a display group to fetch objects, you can fetch enterprise objects directly with an EOEditingContext. Fetching from an EOEditingContext gains you more control over how the objects are fetched and enables you to directly manipulate the object graph. To fetch objects with an editing context involves these steps:
For WebObjects applications, each session has its own editing context which is obtained by sending the defaultEditingContext message to the session:
anEditingContext = [[self session] defaultEditingContext];
To fetch the objects, you must create a qualifier that specifies what objects are qualified for this fetch. For example, to specify that all people having a lastName of "Smith" are qualified to be fetched, use:
aQualifier = [EOQualifier qualifierWithQualifierFormat:@"lastName = 'Smith'"];
3. Build the fetch specification.
Once the qualifier is created, you build the fetch specification. A basic fetch specification defines the entity to which this fetch is targeted, what objects are qualified for the fetch, and the order in which the fetched objects are sorted.
aFetchSpecification = [EOFetchSpecification fetchSpecificationWithEntityName: @"Document" qualifier: aQualifier sortOrderings:nil];
More details of the fetch specification can be specified by invoking the appropriate method to the fetch specification. For example, if you want existing objects to be overwritten with fetched values when they have been updated or changed, you can invoke setRefreshesRefetchedObjects:YES on aFetchSpecification .
When the fetch specification is built, you can fetch the objects from the editing context with the method objectsWithFetchSpecification .
NSArray * results = [aEditingContext objectsWithFetchSpecification: aFetchSpecification];
The results of this fetch is a an array of Enterprise Objects that meets the fetch specification you defined.
EOUtilities Convenience API
The EOUtilities Application Program Interface (API) is a collection of convenience methods to simplify common operations with EOF. It is implemented as a category on EOEditingContext in Objective-C and as an abstract class in Java. To perform the fetch above using EOUtilities use:
NSArray *Smiths = [[[self session] defaultEditingContext] objectsMatchingValue:@"Smith" forKey:@"lastName" entityNamed:@"document"];