C

Candidate class

All objects returned by executing a query or iterating an extent are assignment compatible with the candidate class of the query or extent. The candidate class is also the root of the namespace for field names in the query filter.

Change tracking

A notification mechanism to keep track of the objects and their persistent fields that have changed within the transaction. By using notification, JDO avoids the effort to discover the changes later.

Clean

A persistent object is clean when its transactional fields have not changed within the transaction and its persistent fields are both synchronized with the datastore and have values that were not modified within the transaction.

Clear a field

To set the field's value to its Java default value as determined by its field type.

CMP

Container-managed persistence. Entity EJBs that use CMP allow the container to manage their persistent fields.

CMT

Container-managed transactions. When an EJB is deployed with CMT, the container controls the transaction. As a result, the application code in the EJB cannot control the transaction.

Commit

An operation that ends a transaction by asking the transactional service to apply all changes made within the transaction. When the commit operation succeeds, the service accepts all changes; and when it fails, the service does not accept any changes.

Concurrency value

Some value that indicates, by convention, the version of a data object's persistent state. JDO does not specify how the JDO implementation determines the concurrency value. It might be a timestamp, a version field, a checksum, or some other value. As a result, different JDO implementations may use different types of concurrency values.

CRUD

Acronym for the basic persistent services of Create, Retrieve, Update, and Delete.