休眠-一对多关联

Question

i have two tables, ComputerNode and Connection. ComputerNode has a primary key nodeid but Connection do not have one. I can't modify the table schema. How should i create the java POJO if they were to have one-to-many relationship? basically my objective is to do a inner join like this:

select * from `ComputerNode` cn inner join `Connection` c on cn.nodeid = c.nodeid

Here are the SQL table schema. ComputerNode table:

int nodeid <primary key>;
varchar nodename;

Connection table:

int nodeid <not primary key>;
varchar connstatus;

The relationship between the tables is one-to-many. A computer node can have many connections

I have created two Java POJO classes but i'm not exactly sure about the annotations required. I have read the hibernate tutorial but i don't see explanation on class without a identifier(ie: Connection).

ComputerNode.java:

@Entity
@Table(name="ComputerNodes")
public class ComputerNode {

@Id
@Column(name="nodeid")
private int nodeId;

@Column(name="nodename")
private String nodeName;

@OneToMany
private Set<Connection> connections;

.... //getter and setters
}

Connection.java

//What annotation should i use since this class doesn't have identifier?
public class Connection {

@Column(name="nodeid")
private int nodeId;

@Column(name="connstatus")
private String connStatus;
}

What type of class is Connection supposed to be? @Embeddable? What should I do to create a one-to-many relationship between the two classes?

================

Update

public List<ComputerNode> getComputerNodes() {
    //the query to inner join is:
    return sessionFactory.getCurrentSession().createQuery("from ComputerNode as node inner join Connection as conn").list();
}

for (ComputerNode cn : getComputerNodes) {
 System.out.println(cn.getNodeId() + ',' + cn.getNodeName());

 for (Connection c : cn.getConnections) {
   System.out.println(c.getConnStatus());
 }
}

Answer 1

Try this:

@Entity
@Table(name="ComputerNode")
public class ComputerNode {

@Id
@Column(name="nodeid")
private int nodeId;

@Column(name="nodename")
private String nodeName;

@OneToMany(mappedBy="computerNode")
private Set<Connection> connections;

.... //getter and setters
}

Connections:

@Entity
@Table(name="Connection")
public class Connection {

@ManyToOne
@JoinColumn(name="nodeid")
private ComputerNode computerNode;

...
}

If Connection table doesn't have any primary key, check this solution: Hibernate and table without PK

===========

Updated

If you want to select ComputerNode entities use this query: sessionFactory.getCurrentSession().createQuery("select node from ComputerNode as node").list();

Answer 2

You have to make the Connection class to become an entity also, for you to have a relationship between two entity class just put @Entity on top it

@Entity
@Table(name="Connection")

public class Connection {  
@ManyToOne()
//this will join the nodeId of ComputerNode entity class to Connection entity class
@JoinColumn(name="nodeId")
private ComputerNode nodeId;

@Column(name="connstatus")     
private String connStatus;

}   

hope this will help you.

Answer 3

I'm not really sure what you have to do without id .

Maybe this can help...

@OneToMany (cascade = {CascadeType.ALL}) 
@JoinTable(
    name="Connection",
    joinColumns = @JoinColumn( name="nodeid")
)
private Set<Connection> connections;

best!