java - How to map a PostgreSQL array with Hibernate

Question

has anyone successfully mapped a numeric array in PostgreSQL to a numeric array in java via Hibernate?

sql:

CREATE TABLE sal_emp (name text, pay_by_quarter integer[]);
INSERT INTO sal_emp VALUES ('one', '{1,2,3}');
INSERT INTO sal_emp VALUES ('two', '{4,5,6}');
INSERT INTO sal_emp VALUES ('three', '{2,4,6}');

mapping:

<hibernate-mapping>
    <class name="SalEmp" table="sal_emp">
        <id name="name" />
        <property name="payByQuarter" column="pay_by_quarter" />
    </class>
</hibernate-mapping>

class:

public class SalEmp implements Serializable{
    private String name;
    private Integer[] payByQuarter;
    ...// getters & setters
}

i get an exception when querying the table.

Answer 1

Maven dependency

The first thing you need to do is to set up the following Hibernate Types Maven dependency in your project pom.xml configuration file:

<dependency>
    <groupId>com.vladmihalcea</groupId>
    <artifactId>hibernate-types-52</artifactId>
    <version>${hibernate-types.version}</version>
</dependency>

Assuming you have this table in your database:

create table event (
    id int8 not null, 
    version int4, 
    sensor_names text[], 
    sensor_values integer[], 
    primary key (id)
)

And you want to map it like this:

@Entity(name = "Event")
@Table(name = "event")
@TypeDefs({
    @TypeDef(
        name = "string-array", 
        typeClass = StringArrayType.class
    ),
    @TypeDef(
        name = "int-array", 
        typeClass = IntArrayType.class
    )
})
public static class Event extends BaseEntity {
 
    @Type( type = "string-array" )
    @Column(
        name = "sensor_names", 
        columnDefinition = "text[]"
    )
    private String[] sensorNames;
 
    @Type( type = "int-array" )
    @Column(
        name = "sensor_values", 
        columnDefinition = "integer[]"
    )
    private int[] sensorValues;
 
    //Getters and setters omitted for brevity
}

The string-array and int-array are custom types which can be defined in the BaseEntity superclass:

@TypeDefs({
    @TypeDef(
        name = "string-array", 
        typeClass = StringArrayType.class
    ),
    @TypeDef(
        name = "int-array", 
        typeClass = IntArrayType.class
    )
})
@MappedSuperclass
public class BaseEntity {

    @Id
    private Long id;

    @Version
    private Integer version;

    //Getters and setters omitted for brevity
}

The StringArrayType and IntArrayType are classes offered by the Hibernate Types project.

Testing time

Now, when you insert a couple of entities;

Event nullEvent = new Event();
nullEvent.setId(0L);
entityManager.persist(nullEvent);
 
Event event = new Event();
event.setId(1L);
event.setSensorNames(
    new String[] {
        "Temperature", 
        "Pressure"
    }
);
event.setSensorValues( 
    new int[] {
        12, 
        756
    } 
);
entityManager.persist(event);

Hibernate is going to generate the following SQL statements:

INSERT INTO event (
    version, 
    sensor_names, 
    sensor_values, 
    id
) 
VALUES (
    0, 
    NULL(ARRAY), 
    NULL(ARRAY), 
    0
)
     
INSERT INTO event (
    version, 
    sensor_names, 
    sensor_values, 
    id
) 
VALUES ( 
    0, 
    {"Temperature","Pressure"}, 
    {"12","756"}, 
    1
)