Hibernate Relationship Tutorial – @OneToMany and @ManyToOne (Part 17 to 20 )

Good to know you’ve completed Parts 1 to 16! Thumbs up to you! Otherwise, you can see the links below and follow.

Now we’ll continue with Part 17, focusing on inserting new item to the database using the repository.

• Part 1 to 7 – Setting Up
• Part 8 to 12 – Infinite Recursion, @JoinColumn, JsonManagedReference etc
• Part 13 to 16 – Retrieving Child Records
• Part 17 –  Set up Advanced Rest Client
• Part 18 – Inserting a New Location
• Part 19 – Inserting a New User
• Part 20 – Inserting a New Post
• Part 21 to 28 – Deleting, CascadeTypes and FetchTypes

 

Part 17 – Setup Advanced REST Client

Before you can make  a POST request to the application, you need to have a REST Client (you can’t use the browser!).  For me I use Advanced REST Client. Postman REST Client is ok too.  ARC  is an Add-on to google Chrome. To set it up Advanced REST Client on Google Chrome, follow the steps

Step 1: Follow the link below to setup Advanced REST Client

https://chrome.google.com/webstore/detail/advanced-rest-client/hgmloofddffdnphfgcellkdfbfbjeloo

Step 2: Install it and then launch it. The interface is a shown below

 

 

Part 18: Add New Location

To Insert a new Location we need to make a POST request.

Step 1: Write the AddLocation method in the LocationService. Copy and paste in the LocationService

public void AddLocation(Location location) {
     locationRepository.save(location);
}

 

Step 2: Write the AddLocation method in the LocationController. The method is given below. Copy and paste in the LocationController

 

@PostMapping("/locations/addNew")
public void AddLocation(@RequestBody Location location) {
    locationService.AddLocation(location);
}

 

 

Step 3: Relaunch the application.

Step 4: Make a POST request to the http://localhost:8080/locations/addNew url using Advanced Rest Client. The body of the request is as shown below:

{
    "id": 5,
    "name": "KanysTown"
}

 

Step 5: Now access the http://localhost/locations url to ensure the location is inserted. Then add a couple more locations.

 

Part 19 – Inserting a New User

We would also do the same as we did with adding new Location, but with a little variation. We’ll make some modifications to the User entity and to our data.sql file.

Step 1: Launch the application and access the H2 Console to check  what columns are there in the User table. Notice that there is a column in the User table called location_Id.

Step 2: Open the data.sql file. In the code to insert location, change the location_id to locationid (remove the underscore)

Step 3: Open the User model class. Add a new field named locationid.

Step 4: Add the getters and setters for the new locationid field

Step 5: In the @JoinColumn annotation, change the attribute location_id to locationid.

Step 6: Add new attributes to the @JoinColumn: insertable= false, updatable= false

At the end all the changes you have made is given below:

...
...
@ManyToOne
@JoinColumn(name="locationid", insertable = false, updatable=false)
private Location location;

private Integer locationid;

public Integer getLocationid() {
    return locationid;
}

public void setLocationid(Integer locationid) {
    this.locationid = locationid;
}
...
...

 

Step 7: Open the UserService and add the following code to insert new User

public void UpdateUser(User user) {
	userRepository.save(user);
}

 

Step 8: Open the UserController and add the following code

@PostMapping("/users/addNew")
public void AddUser(@RequestBody User user) {
    userService.AddUser(user);
}

 

Step 10: Launch the application and an try to insert a new user using Advanced REST Client. If it works, thumbs up to you! Otherwise, let me know.

 

Part 20 – Inserting a New Post

Try to make the changes similar to the ones we made to insert a User. Try it and see if you get it, before following the procedure. The procedures are below:

Step 1: Open the data.sql file. Change the post_id to postid for the insert into POST queries.

Step 2: In the Post model, add a new field named postid.

Step 3: Add the getters and setters for the new postid field

Step 4: In the @JoinColumn annotation, change the post_id to postid.

Step 5: Add updatable and insertable attribute and set them to false

At the end, the changes to the  Post model would be as follows:

 

@ManyToOne
@JoinColumn(name="userid", insertable=false, updatable=false)
private User user;

private Integer userid;	

public Integer getUserid() {
    return userid;
}

public void setUserid(Integer userid) {
    this.userid = userid;
}

 

Step 6: Launch the application and make a request using the Advanced REST Client. The Json file is as shown below

{
"id": 4,
"postDate": "2019-09-02T17:42:03.878",
"userid": 2,
"details": "Kindson The Genius"
}

 

Check the H2 Console to ensure that the data inserted correctly.

At this point, you have completed this Part. Thumbs up to you! You are a genius!

Let’s now see how to perform updates on the entities.