ManytoMany creating 2 tables - mysql

Question

I have two classes cards and tags. I want a many to many relationship between them and store the cardId and tagId in one table. When i create the database from the code it creates 2 different table with one to many relationship. tag_cards and card_tags. What am i doing wrong here? I want one single table with many to many relationship.
import javax.faces.bean.ManagedBean;
import javax.persistence.*;
import java.util.Set;
#ManagedBean(name = "addToCardBean")
#javax.persistence.Table(name = "cards")
#Entity
public class Card implements java.io.Serializable{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
public int id;
#Column(name="username",nullable = false)
private String username;
#Column(name="text",nullable = false)
private String text;
#Column(name="author")
private String author;
#Column(name="title")
private String title;
#Column (name="source")
private String source;
#Column(name="facebookID" ,columnDefinition="BigInt(20) default '0'")
private long facebookID;
#ElementCollection(targetClass = Tag.class)
private Set<Tag> tags;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getSource() {
return source;
}
public void setSource(String source) {
this.source = source;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public long getFacebookID() {
return facebookID;
}
public void setFacebookID(long facebookID) {
this.facebookID = facebookID;
}
#ManyToMany(mappedBy = "cards")
public Set<Tag> getTags() {
return tags;
}
public void setTags(Set<Tag> tags) {
this.tags = tags;
}
}
import javax.faces.bean.ManagedBean;
import javax.persistence.*;
import java.util.Set;
#Entity
#Table(name="tag")
#ManagedBean(name="tagBean")
public class Tag implements java.io.Serializable{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
public Integer id;
#Column(name = "tagName", nullable = false)
private String tagName;
#ElementCollection(targetClass = Card.class)
private Set<Card> cards;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getTagName() {
return tagName;
}
public void setTagName(String tagName) {
this.tagName = tagName;
}
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(
name = "cards_tags",
joinColumns = #JoinColumn(name = "id"),
inverseJoinColumns = #JoinColumn(name = "id")
)
public Set<Card> getCards() {
return cards;
}
public void setCards(Set<Card> cards) {
this.cards = cards;
}
}

Answer 1

You are facing this issue because you have used the annotations both at the field and method(getter) level i.e you have mixed both.
#Column(name = "tagName", nullable = false)
private String tagName;
and
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(
name = "cards_tags",
joinColumns = #JoinColumn(name = "id"),
inverseJoinColumns = #JoinColumn(name = "id")
)
public Set<Card> getCards() {
return cards;
}
You have to either use them only on field or only on method(getter). Do not mixup the two.
Why you are ending up with two tables is because the field annotations are getting considered and the many to many mapping is on the getter method which is not being considered.
One way is just use at field level. If annotating at field, change to the following(you need to modify the other entity class as well):
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(
name = "cards_tags",
joinColumns = #JoinColumn(name = "id"),
inverseJoinColumns = #JoinColumn(name = "id")
)
#ElementCollection(targetClass = Card.class)
private Set<Card> cards;
You need to make changes in both classes. Move the annotations from getter to field as described above. Or you have to make changes so that all annotations are on getter instead of field.
Additional links:
https://softwareengineering.stackexchange.com/questions/258541/where-to-put-jpa-annotations-field-or-getter
the difference between anotating a field and its getter method JPA