Basic Annotations in Java Persistence API(JPA)

Hi,

Today we will discuss some of the basic JPA annotations.

Annotations :-

• @Table
• @Column
• @Temporal
• @Transient

Lets consider below table -Company

SNO	NAME	MAIL
1	Google	google@gmail.com
2	Yahoo	yahoo@yahoo.com
3	Microsoft	microsoft@live.com

1.@Table :-is used to map your entity java bean with the table

In general your table name and entity bean will have same name at that time there is no need to use @Table

If the Entity bean is different from the table name we map it by using @Table annotation

Example :-

Lets take the above table-Company ,but my entity bean name is named as Organization  then we can use @Table to map them

@Entity

@Table(name="Company")

Public class Organization{.......}

2.@Column :- is used to map an instance variable with a column in a table

If the variable name and database column name is same ,then there is no need to use column

This is similar to @Table

Example :-

Lets take the data base column -Name in the above table

In Entity bean we have companyName.so how to map them?

@Column(name="Name")

Private String companyName;

3.@Temporal :-

• In Java we have java.util.Date and java.util.Calendar classes,if we wnat to persist them into data base we should use @Temporal
• Temporal are set of time based types

Example :-

@Temporal(TemporalType.DATE)

Date currentDate;

In Entity                                                                   Mapped to data base

TemporalType.DATE	Mapped to java.sql.Date
TemporalType.TIME	Mapped to java.sql.Time
TemporalType.TIMESTAMP	Mapped to java.sql.Timestamp

4.@Transient :-

• Attributes that are part of Entity but should not be persisted should be marked as @Transient
• Suppose we have a attribute lastName and should not be persisted to data base,we use@Transient

Example :-

@Transient

private String lastName;

There are many annotations in JPA,each one of them has special functionality which i will discuss in my later posts

Happy Learning

Please provide your valuable comments on this article and share it across your network.

Contact me @ sudheer@javarecent.com or admin@java-recent.com

Introduction to Entity beans in Java Persistence API (JPA)

Hi All,

In this post we will discuss about Java Persistence API(JPA) entity bean.

Lets have a brief introduction about JPA.

JPA is a Java data base framework which eases interaction with database by providing following features

1. Java Persistence Query language (JPQL)
2. Object relational mapping
3. Providing annotation etc.

The most important aspect in JPA is a Java bean class .

Bean in Java is a simple class with properties and their getter and setter methods

In JPA we call this bean with a special name called as Entity.

Entity Bean :- is an exact replica of a table in a database,it is independent of database used.

• The mapping between a Entity Bean and data base table is configured in persistence.xml file
• There are different types of annotations(@) which helps in representing primary keys,table name etc.
• Annotation are in simple metadata(Data about Data),they give extra information to compiler
• A normal Java bean can be converted into a Entity by using @Entity annotation

we will discuss more about annotations in upcoming posts.

In this post we will see how to write a Entity Bean

Environment used :-

• Eclipse Juno
• Oracle
• JPA 2.0 jars

Lets have below COMPANY table in data base

SNO	NAME	MAIL
1	Google	google@gmail.com
2	Yahoo	yahoo@yahoo.com
3	Microsoft	microsoft@live.com

Now we will write a Entity class for the same. In Eclipse its simple to create most of the required code will be auto generated.

1. Switch to JPA perspective in Eclipse
2. Configure data base connection by using Data Source Explorer view(window-->Show view-->Data Source Explorer)
3. Create a JPA project(File—New-->Create JPA project)
4. Open the project,in JPA content you will find persistence.xml file
5. Now select the project click on new-->others--JPA Entity from tables
6. Select the data base connection , schema configured in step 2 and select tables that you want to generate Entities
7. Click the check box-- update in persistence.xml
8. Select a primary key generator type like Auto etc(Not mandatory) continue and click finish

Lets see the code that gets generated for COMPANY table

@Entity

public class Company implements Serializable {

private static final long serialVersionUID = 1L;

@Id

private BigDecimal sno;

private String mail;

private String name;

public Company() {

}

public String getMail() {

return this.mail;

}

public void setMail(String mail) {

this.mail = mail;

}

public String getName() {

return this.name;

}

public void setName(String name) {

this.name = name;

}

public BigDecimal getSno() {

return this.sno;

}

public void setSno(BigDecimal sno) {

this.sno = sno;

}

}

Explanation :-

Here we need to take a look at two annotations

1. @Entity :- Gives a identification for a normal Java bean as entity
2. @Id :- Indicates the primary key in the table

Here we have three properties and their getter and setter methods,we will be accessing (setting/retrieving )the properties by using these methods.

There are lot more annotations available for various purposes will explain in details in my upcoming posts.

Now have a look at persistence.xml, we will find the Entity class added.

                         Happy Learning

Please provide your valuable comments on this article and share it across your network.

Contact me @ sudheer@javarecent.com or admin@java-recent.com