Four ways to create a primary key in Liferay _liferay

<! DOCTYPE service-builder Public "-//LIFERAY//DTD Service builder 5.0.0//en" "http://www.liferay.com/dtd/ Liferay-service-builder_5_0_0.dtd "> <service-builder package-path=" com.linhopesolutions.canopy "> <

	        namespace>canopy</namespace> <entity name= "Overview" local-service= "true" Remote-service= "false" >
		<!--use a class to generate the primary key. --> <column name= "Overviewid" type= "int" primary= "true" Id-type= "class" id-param= "Com.liferay.counter.service. Persistence. Idgenerator "/> <column name=" text "type=" String "/>" <column name= "published" Type= "boolean"/> <c Olumn name= "Lastmodifiedby" type= "Long"/> <column "name=" Lastmodifiedon "Date" type=/> <column "User"
		Id "type=" Long "/> <finder return-type=" Collection "name=" UserId "> <finder-column name=" UserId "/> </finder> <reference package-path= "Com.liferay.portal.model" entity= "User"/> </enTity> </service-builder>
 

Primay key Field

There are four ways to create the primary key:id-type= "class": In the use of a class to generate the primary, works for all Si Tuations id-type= "increment": Works for all databases supported but not in a clustered enviroment id-type= "identity": Wo Rks for DB2, MySQL, and MS SQL Server. Id-type= "id-type=" sequence "id-param=" id_sequence ": Works for DB2, Oracle, PostgreSQL, and SAP DB. Also LIFERAY-SERVICE-BUILDER_5_0_0.DTD Liferay-service-builder_5_1_0.dtd 6.1.DTD

See the DTD most clearly.

The Id-type and Id-param values are used in order to create a auto-generated, auto-incrementing primary key when Inserti NG records into a table. 
This can is implemented in 4 different ways and depending on the type of database being used. In all cases, the primary key of the model object should is assigned a value of NULL, and Hibernate'll know to replace The null value with an auto-generated, auto-incremented value.

If No id-type value is used, it's assumed that primary key would be assigned and not auto-generated. 

The implementation uses a class to generate a primary key. For example: <column name= "id" type= "Integer" primary= "true" Id-type= "class" id-param= "Com.li Feray.counter.service.persistence.IDGenerator "/> In this implementation," class specified in the Id-param value W  Ill be called to retrieve a unique identifier (in the example above, an Integer) that'll be used as the primary key for The new record. This Implementation supported databases. The second implementation generates identifiers that are a unique only if no other process was inserting data into the SAM E table.

This implementation should is used in a clustered environment, but it does work to all supported.  For example: <column name= "id" type= "Integer" primary= "true" id-type= "increment"/> The third

Implementation uses a identity column to generate a primary key. For example: <column name= ' id ' type= ' Integer ' primary= ' true ' id-type= ' identity '/> in ' this IM Plementation, the CREATE table SQL generated for this entity'll create an identity column that natively auto-generates A primary key whenever an insert occurs.

This implementation are only supported by DB2, MySQL, and MS SQL Server.

The fourth implementation uses a sequence to generate a primary key. For example: <column name= "id" type= "Integer" primary= "true" id-type= "seQuence "id-param=" Id_sequence "/> In this implementation, a CREATE sequence SQL statement are created based on th e id-param value (stored in/sql/sequences.sql). This sequence are then accessed to generate a unique identifier whenever a insert occurs. This implementation are only supported by DB2, Oracle, PostgreSQL, and SAP DB.

So how to create a entity. For example, to create a user, you need to first set the primary key.

Public feed addfeed (feed feed) throws SystemException {
		long feedid = This.counterLocalService.increment ( Feed.class.getName ());
		Feed.setprimarykey (feedid);
		return super.addfeed (Feed);
}

Each of these tables corresponds to a counter

Or:

Long userId = Counterlocalservice.increment ();

The entire database corresponds to a counter

You can view the table counter