firstResult/maxResults specified with collection fetch; applying in memory!

When you specify “left outer join” part of your query, Hibernate will retreive all elements into the memory.

You will see a warning “firstResult/maxResults specified with collection fetch; applying in memory!”. It is used to do pagination correctly.

select distinct department0_.DEPTNO as DEPTNO71_0_, location1_.LOCATION_ID as LOCATION1_54_1_, 
employees2_.EMPNO as EMPNO49_2_, department0_.LOCATION_ID as LOCATION3_71_0_, department0_.DNAME as DNAME71_0_, location1_.DESCRIPTION as DESCRIPT2_54_1_, 
employees2_.DEPTNO as DEPTNO49_2_, employees2_.ENAME as ENAME49_2_, 
employees2_.HIREDATE as HIREDATE49_2_, employees2_.DEPTNO as DEPTNO0__, 
employees2_.EMPNO as EMPNO0__ 
from DEPT department0_ inner join LOCATION location1_ on department0_.LOCATION_ID=location1_.LOCATION_ID 
left outer join EMP employees2_ on department0_.DEPTNO=employees2_.DEPTNO 
where (department0_.DNAME like ?) and employees2_.EMPNO=? order by employees2_.ENAME ASC

How to log Hibernate SQL in to log file?

It is important to log the hibernate sql into log file for debugging purpose.

For this, we need to add a special logger/category named “org.hibernate.SQL” set to “DEBUG” option in log4j.xml

<logger name="org.hibernate.SQL" additivity="false">
    <level value="DEBUG" />
    <appender-ref ref="<LOG_APPENDER>" />
</logger>

Or

<category name="org.hibernate.SQL" additivity="false">
    <priority value="debug"/>
    <appender-ref ref="<LOG_APPENDER>" />
</category>

Additivity denotes whether the log needs to be added into the parent logger or not.

Migration from Spring module to ehcache-spring-annotation

Spring module project is dead. It is no longer supported in Spring 3.0+.

Currently ehcache spring annotations(ESA) provides support to ehcache integrated with Spring in annotated way.

You can move from spring modules to ESA easily.

Refer http://code.google.com/p/ehcache-spring-annotations/wiki/SwitchingFromSpringModules.

Test thoroughly before you make decision.

How to get the current and calling method name in JAVA 5?

To get the current method name

new Throwable().getStackTrace()[ 0 ].getMethodName();

To get the calling method name

new Throwable().getStackTrace()[ 1 ].getMethodName();

Required artifact is missing in Maven

Check for the followings

  1. Check your proxy settings in conf/settings.xml.
  2. Try removing <mirror> if present in conf/settings.xml.
  3. Browse to the maven repository url and ensure required artifacts are present.
  4. Ensure you have proper <repository> configured in pom.xml (not recommended) (or) define your custom profile with repository defined and activated in conf/settings.xml.

Identity Generators in Hibernate

 

Generator Description
increment It generates identifiers of type long, short or int that are unique only when no other process is inserting data into the same table. It should not the used in the clustered environment.
identity It supports identity columns in DB2, MySQL, MS SQL Server, Sybase and HypersonicSQL. The returned identifier is of type long, short or int.
sequence The sequence generator uses a sequence in DB2, PostgreSQL, Oracle, SAP DB, McKoi or a generator in Interbase. The returned identifier is of type long, short or int
hilo The hilo generator uses a hi/lo algorithm to efficiently generate identifiers of type long, short or int, given a table and column (by default hibernate_unique_key and next_hi respectively) as a source of hi values. The hi/lo algorithm generates identifiers that are unique only for a particular database. Do not use this generator with connections enlisted with JTA or with a user-supplied connection.
seqhilo The seqhilo generator uses a hi/lo algorithm to efficiently generate identifiers of type long, short or int, given a named database sequence.
uuid The uuid generator uses a 128-bit UUID algorithm to generate identifiers of type string, unique within a network (the IP address is used). The UUID is encoded as a string of hexadecimal digits of length 32.
guid It uses a database-generated GUID string on MS SQL Server and MySQL.
native It picks identity, sequence or hilo depending upon the capabilities of the underlying database.
assigned lets the application to assign an identifier to the object before save() is called. This is the default strategy if no <generator> element is specified.
select retrieves a primary key assigned by a database trigger by selecting the row by some unique key and retrieving the primary key value.
foreign uses the identifier of another associated object. Usually used in conjunction with a <one-to-one> primary key association.

  

JPA Annotations

AUTO Either identity column, sequence or table depending on the underlying DB  
@Id
@GeneratedValue( strategy = GenerationType.AUTO, generator = “userSeq” )
@SequenceGenerator( name = “userSeq”, sequenceName = “USER_DETAILS_SEQ” )
private Long id; 
TABLE Table holding the id 
<table-generator name=”EMP_GEN”  table=”GENERATOR_TABLE”

   pk-column-name=”key”
            value-column-name=”hi”
            pk-column-value=”EMP”
            allocation-size=”20″/>
//and the annotation equivalent
@javax.persistence.TableGenerator( name=”EMP_GEN”,    table=”GENERATOR_TABLE”,  pkColumnName = “key”, 
valueColumnName = “hi”, 
pkColumnValue=”EMP”,  allocationSize=20) 
IDENTITY Identity column

@Id

@Column( name = “ID”, nullable = false )

@GeneratedValue( strategy = GenerationType.IDENTITY)

private Long id;

SEQUENCE

<sequence-generator name=”SEQ_GEN” sequence-name=”my_sequence”
allocation-size=”20″/>
//and the annotation equivalent
@javax.persistence.SequenceGenerator(name=”SEQ_GEN”,sequenceName=”my_sequence”,
allocationSize=20)

java.lang.NoClassDefFoundError: javax.persistence.spi.ProviderUtil

Ensure that you have jpa 2.0 jar in your classpath. In case of hibernate,ensure hibernate-jpa-2.0-api-XXXX.jar in your classpath.