Representing Array Column in HQL:
Hibernate does not support database arrays (e.g. ones mapped to java.sql.Array
) out of the box.
To Support Array Column of postgres we need to implement custom UserType.
For suppose following is the table syntax which users varchar[] array column
CREATE TABLE posts (title varchar, tags varchar[]);
INSERT INTO posts VALUES ('apple', '{fruit,seasonal}');
INSERT INTO posts VALUES ('badam', '{dry fruit,healthy,tasty}');
INSERT INTO posts VALUES ('coriander', '{leafy vegetables,tasty}');
Following custom UserType (StringArrayType), supports varchar[] column in Postgres.
package com.varam.blog.hql; import java.io.Serializable; import java.sql.Array; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Types; import org.hibernate.HibernateException; import org.hibernate.engine.spi.SessionImplementor; import org.hibernate.usertype.UserType; public class StringArrayType implements UserType { private final int[] arrayTypes = new int[] { Types.ARRAY }; @Override public int[] sqlTypes() { return arrayTypes; } @Override public Class<String[]> returnedClass() { return String[].class; } @Override public boolean equals(Object x, Object y) throws HibernateException { return x == null ? y == null : x.equals(y); } @Override public int hashCode(Object x) throws HibernateException { return x == null ? 0 : x.hashCode(); } @Override public Object nullSafeGet(ResultSet rs, String[] names, SessionImplementor session, Object owner) throws HibernateException, SQLException { // get the first column names if (names != null && names.length > 0 && rs != null && rs.getArray(names[0]) != null) { String[] results = (String[]) rs.getArray(names[0]).getArray(); return results; } return null; } @Override public void nullSafeSet(PreparedStatement st, Object value, int index, SessionImplementor session) throws HibernateException, SQLException { // setting the column with string array if (value != null && st != null) { String[] castObject = (String[]) value; Array array = session.connection().createArrayOf("text", castObject); st.setArray(index, array); } else { st.setNull(index, arrayTypes[0]); } } @Override public Object deepCopy(Object value) throws HibernateException { return value == null ? null : ((String[]) value).clone(); } @Override public boolean isMutable() { return false; } @Override public Serializable disassemble(Object value) throws HibernateException { return (Serializable) value; } @Override public Object assemble(Serializable cached, Object owner) throws HibernateException { return cached; } @Override public Object replace(Object original, Object target, Object owner) throws HibernateException { return original; } }
usage of custom array type in annotation based hibernate model
@Entity @Table(name = "posts", schema = "public") public class Posts extends IEntity { @Column(unique=true, name = "title") private String title; @Column(name = "accountid") @Type(type = "com.varam.blog.hql.StringArrayType") private String[] tags; //Setters and getter methods }
This will also help the hbm2ddl to automatically generate the sql array columns in postgres.