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Oracle Blob/Clob 字段写入时��生�{型异常Cast Exception

java光环 — Tue, 14 Feb 2006 08:35:00 GMT

CLOB clob = (CLOB)us.getStatisticsInfo();

原因�?BR>java.sql.Blob不能强制传唤成oracle.sql.BLOB

解决�Ҏ��如下�Q?BR>
SerializableClob lob=(SerializableClob)us.getStatisticsInfo();
CLOB lob2 = (CLOB)lob.getWrappedClob();
Writer out = lob2.getCharacterOutputStream();

public void testAdd() throws Exception {
        byte[] buffer = new byte[1];
        buffer[0] = 1;
        Session s = null;
        try {
            s = sf.openSession();
            Transaction tx = s.beginTransaction();
            BizUserStatistics us= new BizUserStatistics();
            us.setId(new Long(100));
            us.setStatisticsInfo(Hibernate.createClob(" "));

            s.save(us);
            s.flush();
            s.refresh(us, LockMode.UPGRADE);
//            CLOB clob = (CLOB)us.getStatisticsInfo();
            SerializableClob lob=(SerializableClob)us.getStatisticsInfo();
            CLOB lob2 = (CLOB)lob.getWrappedClob();
            Writer out = lob2.getCharacterOutputStream();
            String fileName = "d:/process_log.sql";
            File f = new File(fileName);
            FileInputStream fin = new FileInputStream(f);

            StringBuffer sb = new StringBuffer();
            for (int i = 0; i < 1000; i++){
                sb.append("" + i + "");
            }
            out.write(sb.toString());
            out.close();

            s.flush();
            tx.commit();
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                if (s != null)
                try {
                s.close();
                } catch (Exception e){}
            }

    }

java光环 2006-02-14 16:35 发表评论

WARN afterTransactionCompletion() was never called

java光环 — Sat, 08 Oct 2005 01:58:00 GMT

WARN:
afterTransactionCompletion() was never called
unclosed connection, forgot to call close() on your session?

警告: afterTransactionCompletion() was never called

执行了tx = session.beginTransaction();

但是后来没处理tx

应该用tx.commit() or tx.rollback()

一般查询时�Ҏ��出现此问�?/P>

java光环 2005-10-08 09:58 发表评论

hibernate ant Hbm2JavaTask Exception of:org.xml.sax.SAXParseException: Attribute "insert" must be declared for element type "discriminator".

java光环 — Fri, 19 Aug 2005 05:52:00 GMT

length="10" force="false" insert="true"/>

Region.hbm.xml(15)
org.xml.sax.SAXParseException: Attribute "insert" must be declared for element type "discriminator".

        at org.apache.xerces.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source)
        at org.apache.xerces.util.ErrorHandlerWrapper.error(Unknown Source)
        at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
        at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
        at org.apache.xerces.impl.dtd.XMLDTDValidator.addDTDDefaultAttrsAndValidate(Unknown Source)
        at org.apache.xerces.impl.dtd.XMLDTDValidator.handleStartElement(Unknown Source)
        at org.apache.xerces.impl.dtd.XMLDTDValidator.emptyElement(Unknown Source)
        at org.apache.xerces.impl.XMLNSDocumentScannerImpl.scanStartElement(Unknown Source)
        at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(
Unknown Source)
        at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
        at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
        at org.apache.xerces.parsers.DTDConfiguration.parse(Unknown Source)
        at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
        at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
        at org.jdom.input.SAXBuilder.build(Unknown Source)
        at org.jdom.input.SAXBuilder.build(Unknown Source)
        at org.jdom.input.SAXBuilder.build(Unknown Source)
        at net.sf.hibernate.tool.hbm2java.CodeGenerator.main(CodeGenerator.java:100)
        at net.sf.hibernate.tool.hbm2java.Hbm2JavaTask.processFile(Hbm2JavaTask.java:149)
        at net.sf.hibernate.tool.hbm2java.Hbm2JavaTask.execute(Hbm2JavaTask.java:97)
        at org.apache.tools.ant.Task.perform(Task.java:341)
        at org.apache.commons.jelly.tags.ant.AntTag.doTag(AntTag.java:185)
        at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:233)
        at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:89)
        at org.apache.maven.jelly.tags.werkz.MavenGoalTag.runBodyTag(MavenGoalTag.java:79)
        at org.apache.maven.jelly.tags.werkz.MavenGoalTag$MavenGoalAction.performAction(MavenGoalTag
.java:110)
        at com.werken.werkz.Goal.fire(Goal.java:639)
        at com.werken.werkz.Goal.attain(Goal.java:575)
        at com.werken.werkz.Goal.attainPrecursors(Goal.java:488)
        at com.werken.werkz.Goal.attain(Goal.java:573)
        at org.apache.maven.plugin.PluginManager.attainGoals(PluginManager.java:671)
        at org.apache.maven.MavenSession.attainGoals(MavenSession.java:263)
        at org.apache.maven.cli.App.doMain(App.java:488)
        at org.apache.maven.cli.App.main(App.java:1239)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:324)
        at com.werken.forehead.Forehead.run(Forehead.java:551)
        at com.werken.forehead.Forehead.main(Forehead.java:581)

build:
----------------------------------
----------------------------------
solution : 升��hiberate verion 2.1.8
----------------------------------
----------------------------------
改maven �Q�project.xml

   hibernate
   hibernate
   2.1.8

    true



�q�样写，也是没有问题�?BR>

java光环 2005-08-19 13:52 发表评论

hiberante persistence

java光环 — Thu, 12 May 2005 10:38:00 GMT

you had a table "miners" that looked like this

create table miners (
   id BIGINT NOT NULL AUTO_INCREMENT,
   first_name VARCHAR(255),
   last_name VARCHAR(255),
   primary key (id)
)

Hibernate class (Miner.java) specifies the fields, getters/setters and xdoclet tags looks like so.

package deadwood;
/**
* @hibernate.class table="miners"
*/
public class Miner {
    private Long id;
    private String firstName;
    private String lastName;
    /**
     * @hibernate.id generator-class="native"
     */
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }

    /**
     * @hibernate.property column="first_name"
     */
    public String getFirstName() { return firstName; }
    public void setFirstName(String firstName) { this.firstName = firstName; }

    /**
     * @hibernate.property column="last_name"
     */
    public String getLastName() { return lastName; }
    public void setLastName(String lastName) { this.lastName = lastName; }
}

Associations

the Miner class we looked at was single table oriented, mapping to a single miners table. ORM solutions support ways to map associated tables to in memory objects ,

Many to One/One to one - belongs_to/has_one
One to Many (set) - has_many
Many to Many (set) - has_and_belongs_to_many
Single Table Inheritance
Components (mapping > 1 object per table)

As a comparative example, lets look at the many to one relationship. We are going to expand our Deadwood example from part I. We add to the Miner a many to one association with a GoldClaim object. This means there is a foreign key, gold_claim_id in the miners table, which links it to a row in the gold_claims table.

(Java)
public class Miner {
   // Other fields/methods omitted

    private GoldClaim goldClaim;
    /**
     * @hibernate.many-to-one column="gold_claim_id"
     *         cascade="save"
     */
    public GoldClaim getGoldClaim() { return goldClaim; }
    public void setGoldClaim(GoldClaim goldClaim) {
        this.goldClaim = goldClaim;
    }
}

Hibernate uses explicit mapping to specify the foreign key column, as well as the cascade behavior, which we will talk about next. Saving a Miner will save its associated GoldClaim, but updates and deletes to it won't affect the associated object.

Transitive Persistence
Its important for an ORM solution to provide a way to detect and cascade changes from in memory objects to the database, without the need to manually save() each one. Hibernate features a flexible and powerful version of this via declarative cascading persistence.

Deleting Hibernate offers a number of different cascading behaviors for all associations types, giving it a high degree of flexibility. For example, setting cascade="all" will make GoldClaim save, update and delete along with its parent Miner, like so...

Miner miner = new Miner();
miner.setGoldClaim(new GoldClaim());
session.save(miner); // Saves Miner and GoldClaim objects.
session.delete(miner); // Deletes both of them.

By using the cascade="save-update", you could get this behavior on any association, regardless of which table the foreign key lives in. Hibernate doesn't base the transistive persistence behavior off the relationship type, but rather the cascade style, which is much more fine grained and powerful.

Query Languages

Hibernate has its own object oriented query language (Hibernate Query Language - HQL), which is deliberately very similar to SQL. How it differs is that it lets developers express their queries in terms of objects and fields instead of tables and columns. Hibernate translates the query into SQL optimized for your particular database. Obviously, inventing a new query language is very substantial task, but the expressiveness and power of it is one of Hibernate's selling points.

Querying for Objects with HQL
when you have to start navigating across objects with SQL, HQL can be very convenient alternative. Let's take a look at our sample queries for HQL.

// Find first Miner by name
Query q = session.createQuery("from Miner m where m.firstName = :name");
q.setParameter("name", "Elma");
Miner m = (Miner) q.setMaxResults(1).uniqueResult();

// Finds up to 10 miners older than 30, ordered by age.
Integer age = new Integer(30);
Query q = session.createQuery(
"from Miner m where m.age > :age order by age asc");
List miners = q.setParameter("age", age).setMaxResults(10).list();

// Similar to join query above, but no need to manually join
Query q = session.createQuery(
"from Miner m where m.goldClaim.squareArea = :area");
List minersWithSqA = q.setParameter("area", new Integer(1000)).list();

Having covered some of the basics of fetching objects, let's turn your attention to how we can make fetching objects fast. The next section covers the means by which we can tune the performance.

Performance Tuning

Beyond just mapping objects to tables, robust ORM solutions need to provide ways to tune the performance of the queries. One of the risks of working with ORM's is that you often pull back too much data from the database. This tends to happen because it its very easy to pull back several thousand rows, with multiple SQL queries, with a simple statement like "from Miner". Common ORM strategies for dealing with this include Lazy fetching, outer join fetching and caching.

What I mean by lazy is that when you fetch an object, the ORM tool doesn't fetch data from other tables, until you request the association. This prevents loading to much unneeded data. Hibernate allows you to choose which associations are lazy. This leads us to one of the great fallacies of ORM, that Lazy loading is always good. In reality, lazy loading is only good if you didn't need the data. Otherwise, you are doing with 2-1000+ queries what you could have done with one. This is dreaded N+1 select problem, where to get all the objects require N selects + 1 original selects. This problem gets much worse when you deal with collections..

Outer Joins and Explicit Fetching

Generally, one of the best way to improve performance is to limit the number of trips to the database. Better 1 big query than a few small ones. Hibernate has a number ways its handles the N+1 issue. Associations can be explicitly flagged for outer join fetching (via outer-join="true"), and you can add outer join fetching to HQL statements. For example...

/**
* @hibernate.many-to-one column="gold_claim_id"
* cascade="save-update" outer-join="true"
*/
public GoldClaim getGoldClaim() { return goldClaim; }

// This does one select and fetches both the Miner and GoldClaim
// and maps them correctly.
Miner m = (Miner) session.load(Miner.class, new Long(1));

In addition, when selecting lists or dealing with collection associations, you can use an explicit outer join fetch, like so...

// Issues a single select, instead of 1 + N (where N is the # miners)
List list = session.find("from Miner m left join fetch m.goldClaim");

The performance savings from this can very significant.

Caching

While object caching isn't always going to be helpful or a performance silver bullet, Hibernate has a huge potential advantage here. It provides several levels of caching, including a session (UnitOfWork) level as well as an optional second level cache. You always use the '1st level' cache, as it prevents circular references and multiple trips to the database for the same object. Using a second level cache can allow much of the database state to stay resident in memory. This is especially useful for frequently read and reference data.

java光环 2005-05-12 18:38 发表评论

关于cascade 与inverse

java光环 — Fri, 15 Apr 2005 07:09:00 GMT

看脓记录�Q?BR>
在绝大多敎ͼ�100%�Q�）情况下，many-to-many的cascade都会讄��?save-update"�Q?
比如User和Role是many-to-many的，你不可能在删除一个Role�Ӟ��把它的所有User都删除吧�Q�反之也不可能�?nbsp;

双向的many-to-many�l�护��h��实比较�ȝ��Q�且效率可能比较低�?
但我始终�q�是坚持一个原则：双向兌��一定要一边设�|��ؓinverse="true"�Q�更新时两边一��h��新。我从来没有遇到�q?SPAN style="FONT-WEIGHT: bold">�q�反外键的情��c�?/SPAN>

从关�p�L��w�来�Ԍ��一对多�Q�多对一的关�p�L��w�都是由多的一�Ҏ��l�护的，
多对多是由双�Ҏ��l�护�?/SPAN>

java光环 2005-04-15 15:09 发表评论