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Programming__WebObjects-EOF-Using EOF-Fetching

Version 7.1 by David LeBer on 2008/03/14 23:41

Overview

There are many ways to specify what Entities to fetch using EOF.

  1. Model a Fetch Specification in EntityModeler
  2. Create a FetchSpecification in code 
  3. Use EOUtilities helper methods
  4. User helper fetch methods in your Entity.java (if generated using a more advanced EOGenerator template).

EOGenerator, Velocity EOGenerator, JavaEOGenerator

For complete details please read the EOF Documentation, the rest of this article will give some simple examples of the different kinds of fetches.

Examples

Model a Fetch Specification in EntityModeler

Create the Fetch Specfication

1. Open your model in EntityModeler and select an Entity to define a fetch spec for.
2. Click on the "New Fetch Specification" tool bar button.
3. In the Properties tab, give the new Fetch Specification a name. ie: userForLoginCredentials
4. Enter a qualifier string in the text area provided. ie: (username = $username) and (password = $password)

Binding variables (eg: $username) will be replaced by user supplied values when the Fetch Specification is called.

Fetch using a Modeled Fetch Specification


String username; //Assume exists
String password; //Assume exists
EOEditingContext editingContext; //Assume exists
NSMutableDictionary bindings = new NSMutableDictionary();
bindings.takeValueForKey(username, Person.USERNAME_KEY);
bindings.takeValueForKey(password, Person.PASSWORD_KEY);
String fetchSpecName = "userForLoginCredentials";
String entityName = Person.ENTITY_NAME;
NSArray objects = EOUtilities.objectsWithFetchSpecificationAndBindings(editingContext, entityName, fetchSpecName, bindings);

Create a Fetch Specification in code

Build a simple qualifier

EOKeyValueQualifier qualifier = new EOKeyValueQualifier(keyName, EOQualifier.QualifierOperatorEqual, value);

Build a more complex qualifier


EOKeyValueQualifier qual1 = new EOKeyValueQualifier(keyName1, EOQualifier.QualifierOperatorEqual, value1);
EOKeyValueQualifier qual2 = new EOKeyValueQualifier(keyName2, EOQualifier.QualifierOperatorEqual, value2);
EOAndQualifier finalQual = new EOAndQualifier(new NSArray(new object[] \{qual1, qual2\}));

Build a Fetch Specification


NSArray sortOrderings; // Assume Exists (or null for no defined sort)
EOQualifier qualifier; // Assume Exists (or null for all objects)
EOFetchSpecification fetchSpec = new EOFetchSpecification("EntityName", qualifier, sortOrderings);

Fetch with the Fetch Specification


String username; //Assume exists
String password; //Assume exists
EOEditingContext editingContext; //Assume exists
EOKeyValueQualifier usernameQual = new EOKeyValueQualifier(Person.USERNAME_KEY, EOQualifier.QualifierOperatorEqual, username);
EOKeyValueQualifier passwordQual = new EOKeyValueQualifier(Person.PASSWORD_KEY, EOQualifier.QualifierOperatorEqual, password);
EOAndQualifier credentialsQual = new EOAndQualifier(new NSArray(new object[] \{usernameQual, passwordQual\}));
EOFetchSpecification userForCredentialsFetchSpec = new EOFetchSpecification(Person.ENTITY_NAME, credentialsQual, null);
NSArray fetchedObjects = editingContext.objectsWithFetchSpecification(userForCredentialsFetchSpec);

 

EOUtilities

EOUtilities has several helper methods for simplifying your fetchs, we've already used "objectsWithFetchSpecificationAndBindings" above.

Also look at:


String username; //Assume exists
EOEditingContext editingContext; //Assume exists
EOEnterpriseObject eo = EOUtilities.objectMatchingKeyAndValue(editingContext, Person.ENTITY_NAME, Person.USERNAME_KEY, username);

EOEditingContext editingContext; //Assume exists
NSDictionary bindings; //Assume exists
EOEnterpriseObject eo = EOUtilities.objectMatchingValues(editingContext, Person.ENTITY_NAME, bindings);

EOEditingContext editingContext; //Assume exists
NSArray objects = EOUtilities.objectsForEntityNamed(editingContext, Person.ENTITY_NAME);

String username; //Assume exists
EOEditingContext editingContext; //Assume exist
NSArray objects = EOUtilities.objectsMatchingKeyAndValue(editingContext, Person.ENTITY_NAME, Person.USERNAME_KEY, username);

EOEditingContext editingContext; //Assume exists
NSDictionary bindings; //Assume exists
NSArray objects = EOUtilities.objectsMatchingValues(editingContext, Person.ENTITY_NAME, bindings);

EOGenerator Template Helper Methods.

Depending on your EOGenerator templates you may have auto generated methods in your Entity.java class that will make fetching objects easier. Look for methods like:


EOEditingContext editingContext; //Assume exists
NSArray people Person.fetchAllPeople(editingContext);

EOEditingContext editingContext; //Assume exists
EOQualifier qualifer; //Assume exists
NSArray people Person.fetchPeople(editingContext, qualifier);