Question

I have a problem with querying Derby database. I am using Hibernate with JPA. Problem is related (probably) to boolean columns. Each query ends with error:

org.hibernate.exception.SQLGrammarException: Comparisons between ‘BOOLEAN’ and ‘INTEGER’ are not supported. Types must be comparable. String types must also have matching collation. If collation does not match, a possible solution is to cast operands to force them to the default collation (e.g. SELECT tablename FROM sys.systables WHERE CAST(tablename AS VARCHAR(128)) = ‘T1’)

Below you may find sample code and configuration. Samples are simplified for easier reading. Here is my JPA entity:

@Entity
public abstract class Task implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    protected long id;

    @Column
    protected boolean deleted;

    public long getId() {
        return id;
    }

    public boolean isDeleted() {
        return deleted;
    }

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

    public void setDeleted(boolean deleted) {
        this.deleted = deleted;
    }

    @Override
    public int hashCode() {
        return id;
    }

    @Override
    public boolean equals(Object object) {
        if (object == null) {
            return false;
        }

        if (!this.getClass().equals(object.getClass())) {
            return false;
        }

        EntityObject other = (EntityObject) object;

        if (this.id != other.id) {
            return false;
        }

        return true;
    }

    @Override
    public String toString() {
        return "EntityObject[ id=" + id + " ]";
    }
}

My JPA query:

SELECT t FROM Task t WHERE deleted = false

My JPA configuration:

<persistence-unit name="PU1" transaction-type="JTA">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<jta-data-source>jdbc/myapp</jta-data-source>
<exclude-unlisted-classes>false</exclude-unlisted-classes>
<properties>
  <property name="hibernate.hbm2ddl.auto" value="update"/>
  <property name="hibernate.dialect" value="org.hibernate.dialect.DerbyDialect"/>
</properties>
</persistence-unit>

What is wrong? How to fix that? Thanks for any suggestions.

Answer 1

Downgrade didn’t helped. Here is valid solution which works for me:

import java.sql.Types;
import org.hibernate.dialect.DerbyTenSevenDialect;

public class DerbyDialect extends DerbyTenSevenDialect {

    public DerbyDialect() {
        // fix Derby dialect boolean data type mapping error
        registerColumnType(Types.BOOLEAN, "INTEGER");
    }
}

I guess it is better to configure ‘true’ and ‘false’ constants mapping in dialect to Derby data type, but above is good enough for now.