Efficiently using Enum in entity class
to improve code maintainability and database performance.

Problems in using Enum in JPA

  • JPA implementations stores the ordinal number of the enum.
  • It is problematic in many ways,
    • We cannot rearrange the enum values.
    • We cannot remove unused enum value.
    • We can add new enum values only at the end.
  • Alternatively, we can use the string representation of the enum.
    • It is too verbose, takes more space.
    • Comparing varchar in database is costly compared to int. Moreover, this field will be used to filter results often.

How to do it right?

In this post we will see how to efficiently use Enum using a int value for each enum value.

  • Create an enum with an int value.
  • Create a class that implements AttributeConverter.
  • Now, simply use the enum wherever required in entity class.

Enum Status

Status has enum values such ACTIVE,INACTIVE, etc.,

package com.sakthipriyan.example;

import java.util.HashMap;
import java.util.Map;

public enum Status {

    // Add any enum values anywhere.
    // Make sure not to repeat same int value.
    // Changing values here, would require update in database as well.
    // Now values stored in database is made explicit in code.
    ACTIVE(1),
    INACTIVE(2),
    CREATED(3),
    SUBMITTED(4),
    ACCPETED(6),
    REJECTED(7);

    private final int value;

    private Status(int value) {
        this.value = value;
    }

    public int getValue() {
        return this.value;
    }

    // This is look up map to get Enum value from int value.
    private final static Map<Integer, Status> map = new HashMap<>();

    // In Enum, static block will be executed after creating all Enum values.
    static {
        for (Status status : Status.values()) {
            map.put(status.getValue(), status);
        }
    }

    public final static Status getStatus(int value) {
        return map.get(value);
    }

}

StatusConverter implements AttributeConverter

AttributeConverter can be implemented to override the default behavior. This implementation say that, Status should be stored as Integer and also provides method to get the Status object from Integer value of the database.

package com.sakthipriyan.example;

import javax.persistence.AttributeConverter;
import javax.persistence.Converter;

@Converter(autoApply = true)
public class StatusConverter implements AttributeConverter<Status, Integer> {

    @Override
    public Integer convertToDatabaseColumn(Status status) {
        return status.getValue();
    }

    @Override
    public Status convertToEntityAttribute(Integer value) {
        return Status.getStatus(value);
    }
}

Enitity Langauge

Now, we can start using the enum Status. Here, Langauge entity has a Status field in it.

package com.sakthipriyan.example;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Language {

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

    @Column(nullable = false)
    private String language;

    @Column(nullable = false)
    private Status status;

    public Language(String language) {
        super();
        this.language = language;
        this.status = Status.ACTIVE;
    }

    public Language() {
        super();
    }

    public short getId() {
        return id;
    }

    public String getLanguage() {
        return language;
    }

    public Status getStatus() {
        return status;
    }

    public void deactivate() {
        this.status = Status.INACTIVE;
    }

    public void activate() {
        this.status = Status.ACTIVE;
    }
}

Result

Now, whenever the Language object is stored in the database. It will persist the Integer equivalent of the Status object rather than using Ordinal number or String representation of the Enum value.

Further tuning

  • Based on the usage, you can even use Short in place of Integer in Status and StatusConverter.
  • Also, you can specify the column size in @Column definition.
  • Alternatively, with minor variations we should be able to easily stores enum values as char(n) say n=2 or n=3.

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About Author

Sakthi Priyan H
Passionate Programmer

  • Sakthi Priyan is passionate about building high quality reliable software.
  • He has vast experience in full stack web since 2006.
  • He primarily codes in Java, Scala and Python.
  • He currently works in backend API services and big data technologies.