The Student class would correspond to the Student table while the Department class would correspond to Department table.<\/p>\n
Now the relationship is such that:<\/p>\n
many student would belong to one department – that is ManyToOne (many students, one department)<\/p>\n
one department can contain many students – that is OneToMany(on department, many students)<\/p>\n
<\/p>\n
How then do we implement this in Spring?<\/strong><\/p>\n So let’s begin with the Student class<\/strong>. This is shown below. Notice that we have included an additional member variable: department.<\/p>\n <\/p>\n In the Student class, we have add the @ManyToOne<\/em><\/strong>\u00a0annotation to the department variable. So, this simply tells hibernate that a student belongs to a department. Also, that many student can have one department.<\/span><\/p>\n Now let’s look at the Department class.<\/strong> This is shown below:<\/p>\n <\/p>\n Also note that in the Department class, we have added a private variable, students. Also notice that this variable is a List<Student> type. This means that we can ask the department to give us a list of students in it!. Isn’t this amazing!<\/p>\n The H2 Console window is shown below;<\/p>\n <\/p>\n Extra Table<\/strong><\/p>\n Now, if you just add the @OneToMany and @ManyToOne annotations, two things would happen:<\/p>\n Somehow, we need a way\u00a0 to tell the Department class that the mapping is handled by the Student class. And therefore it would not be necessary to have a third table.<\/p>\n To do that, we used the mappedBy attribute of the @OneToMany annotation in the Deparment class. The value is set to the field in the Student table that has the @ManyToOne annotation. In our case, this field is the department field.<\/p>\n <\/p>\n I recommend you watch the video as well.<\/p>\n@Entity<\/span>\npublic<\/span> class<\/span> Student<\/span> {<\/span>\n\t\n\t@Id<\/span>\n\tprivate<\/span> Integer Id;<\/span>\n\tprivate<\/span> String firstname;<\/span>\n\tprivate<\/span> String lastname;<\/span>\n\t\n\t@ManyToOne<\/span>\n\tprivate<\/span> Department department;<\/span>\n\t\n\t\/\/constructor<\/span>\n\t\/\/getters and setters<\/span>\n}<\/span>\n<\/pre>\n@Entity<\/span>\npublic<\/span> class<\/span> Department<\/span> {<\/span>\n\t\n\t@Id<\/span>\n\tprivate<\/span> Integer Id;<\/span>\n\tprivate<\/span> String name;<\/span>\n\tprivate<\/span> String description;<\/span>\n\t\n\t@OneToMany<\/span>(<\/span>mappedBy =<\/span> \"department\"<\/span>)<\/span>\n\tprivate<\/span> List<<\/span>Student><\/span> students;<\/span>\n\t\n\t\/\/constructor<\/span>\n\t\/\/getters and setter<\/span>\n}<\/span>\n<\/pre>\n![\"H2](\"https:\/\/www.kindsonthegenius.com\/wp-content\/uploads\/2020\/09\/H2-Console-Window-for-Relationships.jpg\")
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