Java hashmap mapping in database

Question

My entity class is

@Entity
public class Student_enroll implements Serializable {
private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;

private int level_num;
private int term;
private String student_session;
private HashMap<String,Integer>mark_value;

@OneToOne
private Student student;

public String getStudent_session() {
    return student_session;
}

public void setStudent_session(String student_session) {
    this.student_session = student_session;
}



public int getLevel_num() {
    return level_num;
}

public void setLevel_num(int level_num) {
    this.level_num = level_num;
}

public int getTerm() {
    return term;
}

public void setTerm(int term) {
    this.term = term;
}

public Student getStudent() {
    return student;
}

public void setStudent(Student student) {
    this.student = student;
}

public HashMap<String, Integer> getMark_value() {
    return mark_value;
}

public void setMark_value(HashMap<String, Integer> mark_value) {
    this.mark_value = mark_value;
}

public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

@Override
public int hashCode() {
    int hash = 0;
    hash += (id != null ? id.hashCode() : 0);
    return hash;
}

@Override
public boolean equals(Object object) {
    // TODO: Warning - this method won't work in the case the id fields are not set
    if (!(object instanceof Student_enroll)) {
        return false;
    }
    Student_enroll other = (Student_enroll) object;
    if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
        return false;
    }
    return true;
}

@Override
public String toString() {
    return "com.domain.Student_enroll[ id=" + id + " ]";
}

}

and my controller function is

   @RequestMapping(value="/add_mark",method = RequestMethod.POST)
   public void add_mark(HttpServletRequest req){

   HashMap<String,Integer>map=new HashMap<String,Integer>();

   int level=Integer.parseInt(req.getParameter("level"));

   int term=Integer.parseInt(req.getParameter("term"));

   Student_enroll enroll=student_service.get_student_enroll(level, term);

   List<Course>list_course=course_service.list_course(level, term);

   Iterator<Course>itr=list_course.iterator();

    while(itr.hasNext()){

      enroll.put(itr.next().getCourse_Code(),75);
    }

    enroll.setMark_value(map); // Set hashmap 

   student_service.update_student_enroll(enroll);
}

I want to set the HashMap by using setHashmap() and want to persist the entity in database.is it an appropriate way cause when I want to persist it other attribute of entity is persisted but the hashmap attribute contains a BLOB object.

How to persist a hashmap of primitive type?

Can you let us know what is the column type in database for your Entity field private HashMap<String,Integer>mark_value ? — Hirak
– Hirak, Commented Mar 10, 2014 at 5:34
i am using hibernate when i persist a enttity hibernate create the column type according to data type in entity.for example a String data type will be converted to varchar column type.i don't know about hashmap.i mean what column type hibernate will create for hashmap i am not sure. — iftekhar
– iftekhar, Commented Mar 10, 2014 at 5:53
See, relational databases doesnt have a column type HashMap. You can consider hashmap itself as a table, with two columns....and add that to your entity as join columns. — Hirak
– Hirak, Commented Mar 10, 2014 at 6:06
that's absolutely right,but in my case a mark column field is created which value is a BLOB object.I was expecting a table with Student_enroll id and two field coursecode and mark,but that has not happened — iftekhar
– iftekhar, Commented Mar 10, 2014 at 6:12
In that case can you change the column type in entity as byte[]. You will have to convert the hashmap data into byte[] yourself though in some pre-processing step. — Hirak
– Hirak, Commented Mar 10, 2014 at 7:52

mavarazy · Accepted Answer · 2014-03-10 05:32:38Z

1

JPA supports Map persistencse using @MapKey, @MapKeyJoinColumn ... annotations Refer to following article for details:

http://en.wikibooks.org/wiki/Java_Persistence/Relationships#Maps

answered Mar 10, 2014 at 5:32

mavarazy

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2 Comments

iftekhar Over a year ago

mavarazy,thanks for your answer.but those example usese a object in value field of a hashmap.i want to use a prmitive type in the value field of a hashmap.

mavarazy Over a year ago

Autoboxing will automatically convert primitive to appropriate object and vise versa. Maps were designed in Java to handle objects as keys, I would use autoboxing, ignoring performance concerns, that you might have, pursing performance in this case, can have opposite effect.

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