Denodo Hibernate Dialect - User Manual

Last modified on: 06 Oct 2023

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Overview

Hibernate is a framework that provides object/relational mapping (ORM) services for relational databases.

Hibernate is database agnostic. This means that it can work with different databases. However, as databases implement slight variations of the SQL standard, Hibernate includes vendor specific dialects to handle these differences and accomplishes tasks like obtaining a primary key identifier or structuring a SELECT query.

The Denodo Hibernate Dialect is the dialect provided by Denodo to generate the appropriate VQL so Hibernate can deal with Denodo databases.

This dialect supports Hibernate versions 6.1 to 6.3.

Hibernate - Denodo integration

Please note: Hibernate-based applications typically perform a number of write operations as a part of their execution, and some of these write operations might need to be performed in transactional contexts. Please note that the virtual nature of the Denodo Platform as a database sets some limits on what specific views can allow write operations, and what levels of transactionality can be achieved in each case depending on the nature, configuration and specific architecture of the involved data sources. Please refer to the official Denodo documentation for more information on writability and transactionality via JDBC on Denodo views.

JAVA Configuration

Dependencies

You will need to have the following libraries in your classpath:

Hibernate

Denodo VDP JDBC driver

Denodo Hibernate Dialect jar: denodo-hibernate-dialect-<version>.jar in the /dist directory of the Denodo Hibernate Dialect distribution

Properties

You need to add the following property in your Hibernate configuration file:

dialect=com.denodo.connect.hibernate.dialect.DenodoDialect

besides the JDBC connection properties:

connection.driver_class=com.denodo.vdp.jdbc.Driver

connection.url=jdbc:vdb://localhost:9999/database

connection.username=…

connection.password=…

If yours is a Spring Boot application, configuration will look similar to this:

spring.datasource.driver-class-name=com.denodo.vdp.jdbc.Driver

spring.datasource.url=jdbc:vdb://localhost:9999/database

spring.datasource.username=…

spring.datasource.password=…

spring.jpa.properties.hibernate.dialect=com.denodo.connect.hibernate.dialect.DenodoDialect

#Avoids the appearance of HHH000424 in log during startup

spring.jpa.properties.hibernate.jdbc.lob.non_contextual_creation=true

Entity Java class with auto-increment keys

If you need to use primary key values that are automatically generated by the underlying database by means of auto-increment columns, you can do so by using the identity sequence generation strategy in the Denodo Hibernate Dialect. This will only work for JDBC base views created on top of tables with an auto-increment column for their primary key.

Note this feature will only work from:

Denodo 7.0 update 20201116.
Denodo 8.0 update 20210209.

Your entity class will look similar to this:

package …;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.SequenceGenerator;

@Entity
public class Person {

@Id

@GeneratedValue(strategy = GenerationType.IDENTITY)

private int id;

private String name;

private int age;

.............

}

Entity Java class with assigned keys

If you do not need the primary key value to be generated automatically you only have to use the @Id annotation that marks which entity field is the primary key and initialize its value in your application.