org.hibernate.exception.SQLGrammarException: could not initialize a collection

Question

I have 3 tables tbl_category , tbl_Advertisment and tbl_linkcategoryadvert( having many to many association b/w category & advertisment )

My POJO's as given below

Advertisment.java

@Entity
@Table(name="tbl_advertisment")
public class Advertisment implements Serializable {
    private long id;
    private String title;
    private String message;
    private Set<Category> categories;

    public Advertisment(String title, String message) {
        this.title = title;
        this.message = message;
        this.categories=new HashSet<Category>();
    }

    protected Advertisment() {
    }

    @Id
    @GeneratedValue
    protected long getId() {
        return id;
    }

    protected void setId(long id) {
        this.id = id;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    @Column(nullable=false)
    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    @ManyToMany(mappedBy="adverts")
    public Set<Category> getCategories() {
        return categories;
    }

    public void setCategories(Set<Category> categories) {
        this.categories = categories;
    }
}

Category.java

@Entity
@Table(name="tbl_category")
public class Category implements Serializable {
    private long id;
    private String title;
    private Set<Advertisment> adverts=new HashSet<Advertisment>();

    public Category(String title) {
        this.title = title;
    }

    protected Category() {
    }

    @ManyToMany
    @JoinTable(name="tbl_linkcategoryadvert")
    public Set<Advertisment> getAdverts() {
        return adverts;
    }

    public void setAdverts(Set<Advertisment> adverts) {
        this.adverts = adverts;
    }

    public void addAdvert(Advertisment advert){
        adverts.add(advert);
    }

    @Id
    @GeneratedValue
    protected long getId() {
        return id;
    }

    protected void setId(long id) {
        this.id = id;
    }

    @Column(unique=true,nullable=false)
    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }
}

PostAdvert.java - Main class

public class PostAdvertisment extends DAO{

    public Advertisment post(String username,String catTitle,String title,String message) 
            throws DAOException {
        try{
            begin();

            Query categoryQuery=getSession().createQuery("from Category where title=:categoryTitle");
            categoryQuery.setString("categoryTitle", catTitle);
            Category category=(Category)categoryQuery.uniqueResult();

            Advertisment advert=new Advertisment(title,message,user);
            getSession().save(advert);

            category.addAdvert(advert);     
            getSession().save(category);

            commit();

            return advert;
        } catch(HibernateException he){
            he.printStackTrace();
            throw new DAOException(he.getMessage());
        }     
    }

    public static void main(String[] args){

        String catTitle="LCD";
        String title="Bravia";
        String message="High Contrast Television";

        try{
            PostAdvertisment post=new PostAdvertisment();
            post.post(username, catTitle, title, message);
            DAO.close();
        } catch(DAOException daoEx){
            System.out.println(daoEx.getMessage());
        }
    }
}

DAO.java

I'm not providing DAO.java as it only contains Hibernate boilerplate code.

When I run main class I get following exception:

SEVERE: Unknown column 'adverts0_.categories_id' in 'field list'
org.hibernate.exception.SQLGrammarException: could not initialize a collection: [hibernate.Category.adverts#3]
    at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:67)
    at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
    at org.hibernate.loader.Loader.loadCollection(Loader.java:2001)
    at org.hibernate.loader.collection.CollectionLoader.initialize(CollectionLoader.java:36)
    at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:565)
    at org.hibernate.event.def.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:60)
    at org.hibernate.impl.SessionImpl.initializeCollection(SessionImpl.java:1716)
    at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:344)
    at org.hibernate.collection.PersistentSet.add(PersistentSet.java:189)
    at hibernate.Category.addAdvert(Category.java:48)
    at hibernate.client.PostAdvertisment.post(PostAdvertisment.java:35)
    at hibernate.client.PostAdvertisment.main(PostAdvertisment.java:56)
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column 'adverts0_.categories_id' in 'field list'
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
    at com.mysql.jdbc.Util.getInstance(Util.java:384)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1054)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1959)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2113)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2568)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2113)

Please Help me out....

---

My Tables looks like as :

1. tbl_advert

id PK BIGINT
title VARCHAR(255)

2. tbl_category

id PK BIGINT
title VARCHAR(255)

3. tbl_linkcategoryadvert

advert_id FK references(advert.id)
category_id FK references(category.id)

Now my questions are...

1. Am i taking wrong names for fields in table "link_categoryadvert"?
2. how hibernate looks for column names & mappings?
3. what are other possible attributes for @JoinTable Annotation?

Answer 1

Hibernate is generating the column name "categories_id" for your join column, where your table uses the name "category_id". The reference guide has an example of how to map a many-to-many relationship. There are several relevant details in the surrounding text, as well. You should just need to make the mapping on your Category.getAdverts() look something like:

@JoinTable(
    name="tbl_linkcategoryadvert",
    joinColumns=@JoinColumn(name="category_id"),
    inverseJoinColumns=@JoinColumn(name="advert_id")
)