Design of tree structure (hibernate mapping of a tree to database and design of database tables) __ Database

Database model (ID-PID): A father has many children, and a child has only one father, such a structure is a tree. In a database table, the ID and PID (parent_id) are designed. A tree is stored by ID and PID.

From the object-oriented design point of view, in the tree node class is not suitable for PID, a node has 1 or 0 fathers, and 0 or children. So the design is as follows: This is an organizational structure, each institution has its parent and child agencies.

Package com.xie.hibernate.modal;

Import Java.util.HashSet;

Import Java.util.Set;

Import Javax.persistence.CascadeType;

Import javax.persistence.Entity;

Import Javax.persistence.FetchType;

Import Javax.persistence.GeneratedValue;

Import Javax.persistence.Id;

Import Javax.persistence.JoinColumn;

Import Javax.persistence.ManyToOne;

Import Javax.persistence.OneToMany;

@Entity

public class Org {

private int id;

private String name;

Private set<org> childrenorgs=new hashset<org> ();

Private ORG parent;

@Id

@GeneratedValue

public int getId () {

return ID;

}

public void setId (int id) {

This.id = ID;

}

Public String GetName () {

return name;

}

public void SetName (String name) {

THIS.name = name;

}

@OneToMany (mappedby= "parent", Cascade={cascadetype.all},fetch=fetchtype.eager)

Public set<org> Getchildrenorgs () {

return Childrenorgs;

}

public void Setchildrenorgs (set<org> Childrenorgs) {

This.childrenorgs = Childrenorgs;

}

@ManyToOne

@JoinColumn (name= "p_id")

Public Org GetParent () {

return to parent;

}

public void SetParent (ORG parent) {

This.parent = parent;

}

}

The following are the JUnit test methods:

To generate a database table and insert data at the same time:

@Test

Public void Testsave () {

ORG o=new org ();

O.setname ("head Office");

ORG o1=new org ();

O1.setname ("branch 1");

ORG o2=new org ();

O2.setname ("branch 2");

ORG o3=new org ();

O3.setname ("Branch 1 of Branch 1");

ORG o4=new org ();

O4.setname ("Branch 1 of Branch 2");

ORG o5=new org ();

O5.setname ("Branch 2 of Branch 1");

ORG o6=new org ();

O6.setname ("Branch 1 branch 1 branch 1");

O1.setparent (o);

O2.setparent (o);

O3.setparent (O1);

O4.setparent (O1);

O5.setparent (O2);

O6.setparent (O3);

O.getchildrenorgs (). Add (O1);

O.getchildrenorgs (). Add (O2);

O1.getchildrenorgs (). Add (O3);

O1.getchildrenorgs (). Add (O4);

O2.getchildrenorgs (). Add (O5);

O3.getchildrenorgs (). Add (O6);

Try {

Session session=sf.getcurrentsession ();

Session.begintransaction ();

Note added Cascade={cascadetype.all}, only save the node with the whole tree