Nested custom object in Beans

Sailee,

As of now, 'User' table in database has got only three columns let's say firstName, lastName and dateOfBirth and let's say you have also created User Bean class in your Spring code using @Entity annotation like the way we have shown in our code.

Now You want to introduce 'Communication' Bean inside 'User' bean so first User bean will have the reference to Communication and then Communication bean will be separetly created with these two fields email and phone using @Entity annotation and You have created a separate table in database with the same name 'Communication' with these two same fields email and phone.

And You want to create one more bean class with the name 'Phone' with fields countryCode and phoneNumber so again You have create a separate bean class and another table in database with the name 'Phone' with these two very fields(countryCode and phoneNumber)

Now basically, we want to link these three tables:

User with Communication and further Communication with Phone.

As I said, Please create three @Entity classes and three tables in database.

Something like this

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

@Id
@Column(name = "user_id", columnDefinition = "user_id")
private Long userId;

@ManyToMany
@JoinTable(
name = "User_Communication",
joinColumns = @JoinColumn(name = "user_id", referencedColumnName = "user_id"),
inverseJoinColumns = @JoinColumn(name = "communication_id", referencedColumnName = "communication_id"))
@JsonIgnore
private List<Communication> comm;

//Getters and setters
}

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

@Id
@Column(name = "communication_id", columnDefinition = "communication_id")
private Long communicationId;

@ManyToMany
@JoinTable(
name = "Communication_Phone",
joinColumns = @JoinColumn(name = "communication_id", referencedColumnName = "communication_id"),
inverseJoinColumns = @JoinColumn(name = "phone_id", referencedColumnName = "phone_id"))
@JsonIgnore
private List<Phone> phone;

//Getters and setters
}

Phone.java

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

@Id
@Column(name = "phone_id", columnDefinition = "phone_id")
private Long phoneId;

@Column(name = "countryCode", columnDefinition = "countryCode")
private String countryCode;

@ManyToMany
@JoinTable(
name = "Communication_Phone",
joinColumns = @JoinColumn(name = "phone_id", referencedColumnName = "phone_id"),
inverseJoinColumns = @JoinColumn(name = "communication_id", referencedColumnName = "communication_id"))
@JsonIgnore
private List<Communication> comm;

//Getters and setters
}

Something Like this, three bean classes will be linked:

And then we will have to write query using @Query annotation in @Repository class combining these three tables to fetch our data. This we have already seen in our code.

Query can be written something like this:

select <columns>
from User user0_
left outer join communication uc1_ on user0_.user_id=uc1_.user_id, user0_.communication_id=ph1_.communication_id
left outer join Phone up1_ on user0_.user_id=up1_.user_id, user0_.phone_id=up1_.phone_id

You can use @OneToOne/@OneToMany relationship annotation also from User to Communication to Phone depending on your data but make sure ids and fields match like how we are representing in code

Thanks Yogesh for detailed explanation.

I will try to implement the way you have described.

If you uploading new tutorials in future , please do touch base on this concept in video recordings.

Sure Sailee. I will add this very mutil level table concept also in videos.