Am new to JPA...
I have the following preexisting tables inside a MySQL 5 database:
App
User
User_App_Bridge
The relationship(s) are mapped to the User_App_Bridge table (as the name implies, a bridge) amongst App and User as a One to Many cardinality.
The E-R diagram:
User ------ User_App_Bridge------ App
1 User is associated with many apps inside the User_App_Bridge table.
1 App is associated with many users inside the User_App_Bridge table.
The DDL for the User_App_Bridge table:
Code:
CREATE TABLE `User_App_Bridge` (
`User_App_Bridge_Id` int(11) NOT NULL AUTO_INCREMENT,
`User_Id` int(11) NOT NULL,
`App_Id` int(11) NOT NULL,
PRIMARY KEY (`User_App_Bridge_Id`),
KEY `App_Id` (`App_Id`),
KEY `User_Id` (`User_Id`),
CONSTRAINT `user_app_bridge_ibfk_1` FOREIGN KEY (`App_Id`) REFERENCES `App` (`App_Id`))
ENGINE=InnoDB DEFAULT CHARSET=utf8;
Lets say that I have the following JPA Annotated Classes which are mapped to these tables:
Code:
@Entity
public class App {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "App_Id")
private long appId;
@OneToMany
@JoinTable
(
name = "UserAppBridge",
joinColumns = { @JoinColumn(name="App_Id", referencedColumnName = "App_Id") },
inverseJoinColumns = { @JoinColumn(name="User_Id", referencedColumnName = "User_Id") }
)
private List<User> users;
@Column(name = "App_Name")
private String appName;
// Getters & Setter methods
}
Code:
@Entity
public class User {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "User_Id")
private long userId;
@OneToMany
@JoinTable
(
name = "UserAppBridge",
joinColumns = { @JoinColumn(name="User_Id", referencedColumnName = "User_Id") },
inverseJoinColumns = { @JoinColumn(name="App_Id", referencedColumnName = "App_Id", unique = true) }
)
private List<App> apps;
@Column(name = "User_Name")
private String userName;
// Getters & Setter methods
}
Code:
@Entity
public class UserAppBridge {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "User_App_Bridge_Id")
private long userAppBridgeId;
@Column(name = "User_Id")
private long userId;
@Column(name = "App_Id")
private long appId;
// Getters & Setter methods
}
Question(s):
(1) Is this (the block inside the @JoinTable) the correct way to do the one to many mapping for User and App entites with the UserAppBridge?
(2) Inside the @JoinTable should the column & referencedColumnName be assigned to the SQL value (e.g. name="User_Id" , referencedColumnName = "User_Id")
or should it be the Java reference name (e.g. name="userId" , referencedColumnName = "userId")?
(3) Inside the inverseJoinColumns code black, is the unique = true necessary (what is it for)?
(4) Do I need to do anything else inside the UserAppBridge class (for connecting to App and User)?
Thank you for taking the time to read this...
Login
FAQ
Search