Fetch data from multiple tables using eclipselink - eclipselink

Question

This is in response to my question titled "Join tables using eclipselink" asked yesterday.
I will put my scenario here. I have three tables auction, items. one auction can have many items. the mapping between these two tables is through a third table called auctionitems. Below are my tables
CREATE TABLE AUCTION (
auction_id integer,
min_bid_amt decimal(15,2),
max_bid_amt decimal(15,2),
auction_start_ts timestamp,
auction_end_ts timestamp,
owner_id varchar(30),
create_ts timestamp,
last_updt_ts timestamp
);
ALTER TABLE AUCTION ADD CONSTRAINT auction_auction_id_pk PRIMARY KEY(auction_id);
CREATE TABLE ITEM (
item_id integer,
item_name varchar(30),
item_desc varchar(50),
item_image_id integer,
create_ts timestamp,
last_updt_ts timestamp
);
ALTER TABLE ITEM ADD CONSTRAINT item_item_id_pk PRIMARY KEY(item_id);
CREATE TABLE AUCTIONITEMS (
item_id integer,
auction_id integer,
create_ts timestamp,
last_updt_ts timestamp
);
ALTER TABLE AUCTIONITEMS ADD CONSTRAINT item_item_id_fk FOREIGN KEY(item_id) REFERENCES ITEM(item_id);
ALTER TABLE AUCTIONITEMS ADD CONSTRAINT auction_auction_id_fk FOREIGN KEY(auction_id) REFERENCES AUCTION(auction_id);
ALTER TABLE AUCTIONITEMS ADD CONSTRAINT auctionitems_pk_1 PRIMARY KEY(item_id,auction_id);
Now I want to display item_name, item_desc, auction_start_ts and auction_end_ts in my jsp page for all auctions(lets say for 5 auctions).
I am using eclipse link as JPA provider, Tomcat 6.0.29, Spring 3.0.5 and MYSQL 5.1.
These are my domain classes.
Auction :
package com.persistent.eap.domain;
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
import java.sql.*;
#Entity
#Table(name="Auction")
public class Auction implements Serializable
{
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private long auction_Id;
private double min_Bid_Amt;
private double max_Bid_Amt;
private Timestamp auction_Start_Ts;
private Timestamp auction_End_Ts;
private long owner_Id;
private Timestamp create_Ts;
private Timestamp last_Updt_Ts;
public long getAuction_Id() {
return auction_Id;
}
public void setAuction_Id(long auctionId) {
auction_Id = auctionId;
}
public double getMin_Bid_Amt() {
return min_Bid_Amt;
}
public void setMin_Bid_Amt(double minBidAmt) {
min_Bid_Amt = minBidAmt;
}
public double getMax_Bid_Amt() {
return max_Bid_Amt;
}
public void setMax_Bid_Amt(double maxBidAmt) {
max_Bid_Amt = maxBidAmt;
}
public Timestamp getAuction_Start_Ts() {
return auction_Start_Ts;
}
public void setAuction_Start_Ts(Timestamp auctionStartTs) {
auction_Start_Ts = auctionStartTs;
}
public Timestamp getAuction_End_Ts() {
return auction_End_Ts;
}
public void setAuction_End_Ts(Timestamp auctionEndTs) {
auction_End_Ts = auctionEndTs;
}
public long getOwner_Id() {
return owner_Id;
}
public void setOwner_Id(long ownerId) {
owner_Id = ownerId;
}
public Timestamp getCreate_Ts() {
return create_Ts;
}
public void setCreate_Ts(Timestamp createTs) {
create_Ts = createTs;
}
public Timestamp getLast_Updt_Ts() {
return last_Updt_Ts;
}
public void setLast_Updt_Ts(Timestamp lastUpdtTs) {
last_Updt_Ts = lastUpdtTs;
}
}
Item :
package com.persistent.eap.domain;
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
import java.sql.*;
#Entity
#Table(name="Item")
public class Item implements Serializable
{
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private long item_Id;
private String item_Name;
private String item_Desc;
private int item_Image_Id;
private Timestamp create_ts;
private Timestamp last_updt_ts;
public long getItem_Id() {
return item_Id;
}
public void setItem_Id(long itemId) {
item_Id = itemId;
}
public String getItem_Name() {
return item_Name;
}
public void setItem_Name(String itemName) {
item_Name = itemName;
}
public String getItem_Desc() {
return item_Desc;
}
public void setItem_Desc(String itemDesc) {
item_Desc = itemDesc;
}
public int getItem_Image_Id() {
return item_Image_Id;
}
public void setItem_Image_Id(int itemImageId) {
item_Image_Id = itemImageId;
}
public Timestamp getCretae_ts() {
return create_ts;
}
public void setCretae_ts(Timestamp cretaeTs) {
create_ts = cretaeTs;
}
public Timestamp getLast_updt_ts() {
return last_updt_ts;
}
public void setLast_updt_ts(Timestamp lastUpdtTs) {
last_updt_ts = lastUpdtTs;
}
}
AuctionItems:
package com.persistent.eap.domain;
import java.io.Serializable;
import java.sql.Timestamp;
import javax.persistence.Entity;
#Entity
public class AuctionItems implements Serializable{
private static final long serialVersionUID = 1L;
private int itemId;
private int auctionId;
private Timestamp createTs;
private Timestamp lastUpdtTs;
public AuctionItems(){
}
public int getItemId() {
return itemId;
}
public void setItemId(int itemId) {
this.itemId = itemId;
}
public int getAuctionId() {
return auctionId;
}
public void setAuctionId(int auctionId) {
this.auctionId = auctionId;
}
public Timestamp getCreateTs() {
return createTs;
}
public void setCreateTs(Timestamp createTs) {
this.createTs = createTs;
}
public Timestamp getLastUpdtTs() {
return lastUpdtTs;
}
public void setLastUpdtTs(Timestamp lastUpdtTs) {
this.lastUpdtTs = lastUpdtTs;
}
}
In AuctionItems there is no #Id because it is a composite primary key. I do not know how to put a composite primary key. And JPA complains that this class is not a known Entity type.
And finally my persistence.xml file
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<persistence-unit name="portalintegrator" transaction-type="RESOURCE_LOCAL">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<class>com.persistent.eap.domain.UserDetails</class>
<class>com.persistent.eap.domain.Item</class>
<class>com.persistent.eap.domain.Auction</class>
<properties>
<property name="eclipselink.jdbc.driver" value="com.mysql.jdbc.Driver" />
<property name="eclipselink.jdbc.url" value="jdbc:mysql://localhost:3306/portaldemo" />
<property name="eclipselink.jdbc.user" value="root" />
<property name="eclipselink.jdbc.password" value="root" />
<property name="eclipselink.ddl-generation" value="None" />
<property name="eclipselink.logging.level" value="INFO" />
<property name="eclipselink.target-database" value="MYSQL" />
</properties>
</persistence-unit>
</persistence>
I have a couple of questions?
If I use JPA annotations how would I achieve this?
If I use JPQL what is the query going to look like to fetch the above 4 fields?

Answer 1

Normally you would use a #ManyToMany mapping to map a join table, your Auction would have an items field of List.
See,
http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany
You join table seems a little more complex, with additional fields, so you may also want to map it an an Entity, see,
http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany#Mapping_a_Join_Table_with_Additional_Columns