Hibernate

FAQ What's New

Your Trail database > Hibernate Table of Contents [show]     1 Introduction     2 Installation     3 A simple hibernate example     4 Hibernate architecture     5 Acquisition Attempt Failed!!! Clearing pending acquires     6 ObjectVisualizer     7 Links     8 NoClassDefFoundError: javax/transaction/Synchronization     9 could not initialize proxy - the owning Session was closed     10 I lost all my data every time I restart my jboss and hibernate, what's wrong?     11 I got weird errors about NonUniqueObjectException     12 I got errors about failed to initialize hibernate, duplicate xx.hbm.xml     13 I have a datetime field, how come I only get to set date?     14 org.hibernate.exception.JDBCConnectionException: could not execute query     15 org.hibernate.NonUniqueObjectException Keywords JDBC Copyright Information This article is licensed under GNU Public License. Some of the images in this article may have different copyright licenses. Please follow the URLs of the images for detailed information about their specific copyright licenses. Contact webmasters for more information on copyright issues. 1 Introduction Hibernate is a Java persistence layer toolset. It maps between Java classes to database tables and from Java data types to SQL data types, bidirectionally. Hibernate also provides data query and retrieval facilities. The whole purpose of Hibernate was to reduce development time otherwise spent with manual data handling in SQL and JDBC. 2 Installation Download a copy of Hibernate from Hibernate website run ant to install hibernate test your hibernate installation update etc/hibernate.properties according to your system configuration make sure your JDBC driver is in $HIBERNATE_HOME/lib run "ant eg" 3 A simple hibernate example Trust me, hibernate has excellent documentations, you'll see after you try this out. Following the instructions step by step in Chapter 2 of the hibernate tutorial. It's one of the best documentations I've ever seen. Basically you need to do the following to try out your first hibernate applicaiton. create your directory architecture: A src directory for holding Person.java, Event.java, Person's hibernate mapping file Person.hbm.xml, Event's hibernate mapping file Event.hbm.xml, and the hibernate configuration file hibernate.cfg.xml. A lib directory containing the following list of .jar files: antlr.jar, cglib-full.jar, asm.jar, asm-attrs.jars, commons-collections.jar, commons-logging.jar, ehcache.jar, hibernate3.jar, jta.jar, dom4j.jar, log4j.jar, and hsqldb.jar. Note that some jar filenames might be slightly different from the filenames listed here. They may contain version nubmers etc. copy the jar files to the lib directory add java code or xml config elements into the xml and java files add build.xml into the main directory final directoy structure . +lib +src Event.java Event.hbm.xml HibernateUtil.java hibernate.cfg.xml +data build.xml ant compile; ant run -Devent=aaa 4 Hibernate architecture The following figure shows the basic hibernate architecture[TUTORIAL] 5 Acquisition Attempt Failed!!! Clearing pending acquires This may have been caused by hibernate not being able to connect to database server. 6 ObjectVisualizer ObjectVisualizer is a hibernate-based table object viewer toolkit. Here is a demo http://objectvisualizer.com/files/ov-demo.htm. 7 Links hibernate mapping cheatsheet hibernate example tutorial 8 NoClassDefFoundError: javax/transaction/Synchronization Need to include jta.jar in your class path 9 could not initialize proxy - the owning Session was closed LIE error (lazy initialization error). A dirty fix is to turn off lazy initialization in .hbm.xml. For example: <many-to-one name="source" column="source" class="Source" lazy="false"/> 10 I lost all my data every time I restart my jboss and hibernate, what's wrong? Check you hibernate.cfg.xml and see if it has the following line: <property name="hibernate.hbm2ddl.auto">create</property> This line tells hibernate to recreate the tables every time it restarts 11 I got weird errors about NonUniqueObjectException close session, then reopen it, then update() 12 I got errors about failed to initialize hibernate, duplicate xx.hbm.xml restart you eclipse 13 I have a datetime field, how come I only get to set date? Even though you set the field to new Date(). Are you using "date" in your hibernate mapping? Use timestamp instead. 14 org.hibernate.exception.JDBCConnectionException: could not execute query You could have so many connections hanging around that mysql doesnot have more connections to give out. 15 org.hibernate.NonUniqueObjectException org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session The session maintains a unique mapping between persistent identity and object instance, in order to help you avoid data aliasing problems. You cannot simultaneously attach two objects with the same class and identifier to the same session. The best way to avoid any possibility of this exception is to always call saveOrUpdate() at the beginning of the transaction, when the session is empty. In Hibernate3, you can try using the merge() operation, which does not reattach the passed instance. Comments #1, at May 15, 2008 04:18:55, hjhkj said: jhfkjfkgfkjh/;ol;' References [TUTORIAL] http://www.hibernate.org/hib_docs/v3/reference/en/html/architecture.html Webster Unabridged Hi"ber*nate (?), v. i. [imp. & p. p. Hibernated (?); p. pr. & vb. n. Hibernating (?).] [L. hibernare, hibernatum, fr. hibernus wintry. See Hibernal.] To winter; to pass the season of winter in close quarters, in a torpid or lethargic state, as certain mammals, reptiles, and insects. Inclination would lead me to hibernate, during half the year, in this uncomfortable climate of Great Britain. Southey. (search time: 341.148 msec) English-Chinese hibernate ['haib2neit] ¹ý¶¬,¶¬Ãß,±Üº® (search time: -914.262 msec)