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| <th class="tableblock halign-left valign-top">Term</th> |
| <th class="tableblock halign-left valign-top">Definition</th> |
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| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="application-identity"></a>application identity</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">When the persistence |
| of a class is defined in a MetaData file, the developer can decide that |
| they want to control the identity of objects of that class. This is |
| called <strong>application identity</strong> because the application has the control.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="attach-detach"></a>attach/detach</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">When you have an object of a class |
| that is associated with a PersistenceManager it is referred to as being |
| <em>attached</em>. If you want to stop persistence of that object you can |
| <em>detach</em> the object. This has the effect that any changes to the object |
| will not be persisted, and also that the object can be used outside |
| transactions.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="datastore-identity"></a>datastore identity</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">When the persistence of a |
| class is defined in a MetaData file, the developer can decide that they |
| want the identity of objects of that class to be defined by the JDO |
| implementation. This is called <strong>datastore identity</strong></p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="default-fetch-group"></a>default-fetch-group (DFG)</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">When a persisted |
| object is retrieved from the datastore its fields can be retrieved with |
| it, or optionally can be retrieved only when needed. If a field is in |
| the <strong>default-fetch-group</strong> it will be retrieved when the object is |
| retrieved. Some field types default to being in the |
| <strong>default-fetch-group</strong> (e.g primitives, wrappers to primtives, |
| java.util.Date) and others (e.g java.util.Set, java.util.List) don’t.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="embedded"></a>embedded</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">A field can be defined as embedded if it will |
| be stored as a column in the table of its containing object.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="enhancer"></a>enhancer</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">JDO 1.0.1 requires the use of a byte-code |
| enhancer that takes the Java compiled classes and "enhances" them, |
| adding in information to permit their use in a JDO environment.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="fco"></a>FCO</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">JDO defines 2 main groups of Java objects. The first is |
| those objects that have an identity. These are termed "First Class |
| Objects" or FCO for short.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="fetchgroup"></a>Fetch Group</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">JDO allows a user to define groups of |
| fields that should be retrieved (fetched) at the same time. These are |
| called a "fetch group". The principal "fetch group" is the "default |
| fetch group", where JDO has rules for what fields are in this group. A |
| user can define their own group, and make this active so that when |
| objects of their type are retrieved, they have control over the fetching |
| process.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="JDOQL"></a>JDOQL</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">JDO introduces its own Java-like query language as a |
| datastore independent way of retrieving objects from the datastore. This |
| is known as JDOQL (JDO Query Language).</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="nondurable-identity"></a>nondurable identity</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">Where the objects of a |
| class should be unique in the JVM but not in the datastore (where an |
| RDBMS table doesnt have a PK for example).</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="objectid-class"></a>objectid class</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">When an object of a class is |
| persisted, it is assigned an object identity. When the developer has |
| chosen to use <a href="#application-identity">application identity</a> they can |
| assign a class to represent this identity (as a primary key) - this is |
| the object id class.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="optimistic-transaction"></a>optimistic transaction</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">When working with |
| long duration transactions it is undesirable to have locking and so the |
| assumption is made that the data being updated by the transaction will |
| not be modified by any other transaction during the course of the |
| (optimistic) transaction. The data is checked just before commit to |
| confirm integrity that no data has been changed. See also |
| <a href="#pessimistic-transaction">pessimistic transaction</a> for the contrary |
| type which provides locking.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="persistence-by-reachability"></a>persistence-by-reachability</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">When you |
| call makePersistent() on an object, the object will be persisted and, in |
| addition, any other objects reachable from that object (via |
| relationships) will also be persisted. This is known as |
| <strong>persistence-by-reachability</strong>. This process is repeated at commit() time |
| when it checks whether these reachable objects are still reachable and, |
| if not, removes them from persistence.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="persistence-aware"></a>persistence-aware</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">When an class needs to |
| access fields of a persistence capable class directly, it should be |
| enhanced, and is referred to as "Persistence Aware". If a class uses |
| field accessor methods then it doesnt need to become "Persistence |
| Aware".</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="persistence-capable"></a>persistence-capable (PC)</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">When an class is |
| byte-code enhanced, and has valid MetaData, it is referred to as |
| "Persistence Capable". This means that it can be persisted by a JDO |
| implementation.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="persistence-modifier"></a>persistence-modifier</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">When defining the |
| persistence of a class, the developer can select particular fields to be |
| persisted, and others not depending on their importance in the scope of |
| their application. The <strong>persistence-modifier</strong> defines whether a field is |
| persistent. If this tag is not specified JDO will assign defaults based |
| on the field type (primitives, primitive wrappers, java.util.Data, |
| persistence capable fields, etc are by default persistent).</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="persistent"></a>persistent</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">This is an object state where the object |
| is persistent in a datastore.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="pessimistic-transaction"></a>pessimistic transaction</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">This is the |
| default transaction type in JDO, and is suitable for shortlived |
| operations where there is no other blocking activity during the |
| transaction. When data is accessed other transactions are locked out |
| from accessing it until the transaction is complete. See also |
| <a href="#optimistic-transaction">optimistic transaction</a> for the contrary |
| type which reduces locking.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="requires-extent"></a>Requires Extent</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">When the persistent of a class |
| is defined, the developer decides if the object will be stored with its |
| own identity (in its own table for example) or whether it will be stored |
| as part of another object. If it will have its own identity, it will |
| require and Extent.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="sco"></a>SCO</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">JDO defines 2 main groups of Java objects. The second |
| group is those objects that don’t have an identity. These are termed |
| "Second Class Objects" or SCO for short.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="SQL"></a>SQL</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">JDO allows use of multiple query languages. One of |
| these, for use with RDBMS datastores, is SQL.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a id="transient"></a>transient</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">This is an object state where the object is |
| not persistent.</p></td> |
| </tr> |
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