How to Map a PostgreSQL JSON Column to a Hibernate Entity Property?

Mapping PostgreSQL JSON Column to a Hibernate Entity Property

Introduction

Integrating data from a PostgreSQL JSON column into a Hibernate entity can pose challenges. The JSON type in PostgreSQL requires a specific mapping strategy for seamless interaction with an entity property. This article explores the approaches available to establish this mapping, providing code snippets and a real-world example for a custom user type implementation.

Identifying the Data Type

When attempting to map a PostgreSQL JSON column to a JPA2 Entity field, using String as a data type may lead to conversion issues. The correct value type depends on the specific requirements and mapping strategy used.

Custom User Type

To map a JSON column to an entity property, you can define a custom Hibernate UserType. This allows for direct mapping of String values to the database's JSON type. Here's an example implementation:

<code class="java">import org.hibernate.HibernateException;
import org.hibernate.engine.spi.SessionImplementor;
import org.hibernate.usertype.UserType;

import java.io.Serializable;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Types;

public class StringJsonUserType implements UserType {
    // Implementation details here...
}</code>

Defining the UserType

The custom user type is annotated in the entity class:

<code class="java">@TypeDefs( {@TypeDef( name= "StringJsonObject", typeClass = StringJsonUserType.class)})</code>

Property Annotation

The entity property is annotated to use the custom user type:

<code class="java">@Type(type = "StringJsonObject")
public String getBar() {
    return bar;
}</code>

Configuring the Database

Hibernate will handle creating the column with JSON type in the database based on the entity mapping.

Example Project

A GitHub project is available for further exploration:

https://github.com/timfulmer/hibernate-postgres-jsontype

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