Why hibernater1
- 1. Why Hibernate? Learning By Evolution Presented by 4 Circles LLC 4 Circles Copyright
- 2. Pre ORM ORM – Object Relational Mapping. This is the main concept in Hibernate. In a typical environment, we have the usual n-tier architecture as shown v1.01 copyright 4 Circles
- 3. Pre ORM In a standard Model View Controller (MVC) architecture the ‘mapping of the objects’ was done by the Controller. The majority of all work done is retrieiving data from databases to the view. While retrieving of data can be done using native database SQL the data which is shown in the view is different. Here we say ‘mapping of the objects’. v1.01 copyright 4 Circles
- 4. Pre ORM Disadvantages Everyone wrote their own mapping of objects in each controller for the same table. Maintenance was not easy. Table changes then all the code needs to change to map correctly the objects. Same programmer had to do the same mapping for another application with the same table v1.01 copyright 4 Circles
- 5. Object Relational Mapping Complicated applications required more programmers to share their code. In the early 2000s, each programmer wrote their own ORM tool, e.g. <orm> <table name=“employee” object=“EmployeeDTO”> <column name=“id” field=“employeeId”/> <column name=“fname” field=“firstname”/> <column name=“lname” field=“lastname”/> </table> </orm> As can been seen above to read the above XML we need one class and generate the objects to send to the view. This can be extended to many tables without loss of generality. Easy to maintain. v1.01 copyright 4 Circles
- 6. Object Relational Mapping This method was good however, not standardized thru the industry. As each new programmer came on board a new project you had different flavors of home-grown ORMs in the same application. A few people got together and came up with Hibernate to work on JDK 1.4.x. They put some standards and got the engine to map the table to the objects in the same way we saw in the previous slide. Disadvantages of XML file: If the code changes then the xml file need to updated and vice-versa. Specifically when we add a new column then the java file and the xml file need to be updated. Not self-contained. v1.01 copyright 4 Circles
- 7. JPA with Hibernate With JDK1.5.x, the concept of annotations was introduced and with that Java Persistence Annotations (JPA) were introduced. JPA then eliminated the need to have an XML file to map the columns to each object’s member variable. v1.01 copyright 4 Circles
- 8. A Simple Example package com.fourcircles.learning.jpa; @Entity @NamedNativeQuery(name = SimpleEntity.QUERY_BY_SIC_CODE, query = " SELECT " + b.FTA_CODE AS fta_code, b.DIVISION_NM AS division_name, b.Company_name as office_name, b.MKT AS market_name, " NVL(b.FTA_DESCRIPTION, 'UNKNOWN') AS fta_description, b.BILLING_SYSTEM_NAME AS billing_system_name" + " FROM busmap.busmap_fin_hierarchy@busmap b WHERE "+ " ( length(fta_code) > 8 AND b.SIC_CODE = :"+ SimpleExample.SIC_CODE, resultSetMapping="companyMapping" ) @SqlResultSetMapping(name = "marketMapping", entities = { @EntityResult(entityClass = com.fourcircles.learning.jpa.SimpleExample.class, fields = { @FieldResult(name = "ftaCode", column = "fta_code"), @FieldResult(name = "divisionName", column = "division_name"), @FieldResult(name = "companyName", column = "company_name"), @FieldResult(name = "marketName", column = "market_name"), @FieldResult(name = "ftaDescription", column = "fta_description"), @FieldResult(name = "billingSystemName", column = "billing_system_name") }) }) public class SimpleExample { public final static String QUERY_BY_SIC_CODE = “infoBySICCode"; public final static String QUERY_PARM_FTA_CODE = “sicCode"; @Id private String ftaCode; private String divisionName; private String marketName; private String companyName; private String ftaDescription; private String billingSystemName; public MarketDTO() { public void setOfficeName(String companyName) { this.companyName = companyName; } } v1.01 copyright 4 Circles