How to change the way objects are returned in spring-data/hibernate/rest

Question

I'm working on a REST application with Spring-data Hibernate etc.. I've setup all my basic actions but now I want to do something specific. When i retrieve a list of items which have a foreign key to another table in my database, hibernate will return the entire row of that foreign key. For example:

[ {
  "id":1, 
  "school": {"id":1, "name":"De regenboog", password":"800e30e9bb3b82ce955a127650d835d0", "street":"Plantaanstraat", "number":"2", "zipCode":"1234AS", "city":"Amsterdam", "contactName":"Arends", "contactPhoneNumber":"06-45648466", "contactEmail":"arends@regenboog.nl"}, 
  "name":"Groep", 
  "dateCreated":"2012-04-25"
  }
]

(These are all fictional data by the way)

Now the thing is is don't want the school to be returned in its entirety. I just want to show the school_id. I've searched around the web and read some things about "service level mapping" but I was unable to find any examples. I've built my application with a

controller -> service -> dao -> repository

setup.

I hope you guys can help me out! (let me know if you need more source code as well).

Thanks alot

EDIT

The thing I want to add is that my MySql table looks like this:

ID | SCHOOL_ID | NAME | DATE_CREATED

So what i'd like to have returned is just the plain school_id instead of the object school (in this situation)

EDIT2 I'm working on @Dandy answer and I want to show the code I have now:

@ManyToOne
@JoinColumn(name = "SCHOOL_ID")
private School school;

@Column(name = "SCHOOL_ID", insertable = false, updatable = false)
private long schoolId;

public long getSchoolId() {
    return schoolId;
}

public void setSchoolId(long schoolId) {
    this.schoolId = schoolId;
}

public School getSchool() {
    return school;
}

public void setSchool(School school) {
    this.school = school;
}

When i change the code like Danny suggested, I get the result that I want.. almost. This is what I get if I run the query now:

[ {
  "id":1, 
  "school": {"id":1, "name":"De regenboog", password":"800e30e9bb3b82ce955a127650d835d0", "street":"Plantaanstraat",  "number":"2", "zipCode":"1234AS", "city":"Amsterdam", "contactName":"Arends", "contactPhoneNumber":"06-45648466", "contactEmail":"arends@regenboog.nl"},    
  "schoolId": 1  
  "name":"Groep", 
  "dateCreated":"2012-04-25"
  }
]

The thing is that I want to disable the school for this particular query. Is that possible?

Answer 1

A few days have passed and I found a solution that worked for me. I made some new classes IE SchoolDTO (DTO stands for Data Transfer Object). Inside these classes I only added the values I wanted to show to the front end. ie:

public class ClassesDTO {

    private long id;
    private long schoolId;
    private String schoolName;
    private String name;
    private Date dateCreated;

    //Getters and setters...
}

Instead of showing the entire School object I only included it's ID and NAME. Inside this class there are only getters and setters. Then I make a mapper which will map the original Classes to the new DTO Class. ie.

public ClassesDTO mapToDTO(Classes classes) {
    ClassesDTO classesDTO = new ClassesDTO();
    classesDTO.setId(classes.getId());
    classesDTO.setSchoolId(classes.getSchool().getId());
    classesDTO.setSchoolName(classes.getSchool().getName());
    // etc...

Then in my service layer I return the new mapped DTO object to my controller instead of the normal Classes object.

And that's all actually. I also have a mapping if I need to return a java.util.List and the other way around if I want to insert data into my database without having to declare the entire school. I'll show a quick example of this just someone is wondering how I did this:

public Classes mapFromDTOCreate(ClassesCreateDTO classesCreateDTO){
    Classes classes = new Classes();
    classes.setSchool(schoolDAO.findSchoolById(classesCreateDTO.getSchoolId()));
    classes.setName(classesCreateDTO.getName());
    classes.setDateCreated(classesCreateDTO.getDateCreated());
    return classes;
}

This new classes object I can safely return to my DAO which hibernate can save to my database cause of the ORM (Object relational mapping).

If anyone has any questions please let me know!

Answer 2

Currently the school might be mapped using a <many-to-one> relationship.

<many-to-one name="school" class="School">
    <column name="SCHOOL_ID" type="string" />
</many-to-one>

You can delcare one more field for SCHOOL_ID.

<property name="schoolId" column="SCHOOL_ID" type="string" insert="false" update="false"/>

Note: insert="false" update="false" is needed if a column is mapped more than once.

Answer 3

If you are using the (default) Jackson mapper for JSON serialization, you can annotate properties with @JsonIgnore in your entities if you don't want them to be serialized.