mariusneo / postgres-json-jpa

Proof of Concept on how to deal generically with several entities stored in one table

spring-data-jpa usage of Postgres JSONB fields

This simple project can be used as PoC in storing generically data in JSONB fields. In a scenario where profession specific information would be stored in joined tables, with the help of JSONB fields in Postgres we can store all the information in one table and avoid the table joins needed to retrieve all the required information about a person.

What this PoC brings new is that specific entities :

• Student
• Professor

can be handled in a type-safe manner :

• Student class has a StudentInfo field
• Professor class has a ProfessorInfo field

On the other hand, if some batch processes need to deal with all the persons, this can be done with the help of CommonPerson class (and associated CommonPersonRepository).

The table containing the persons (generated here by Hibernate) looks like this :

CREATE TABLE person
(
  dtype character varying(31) NOT NULL,
  id bigint NOT NULL,
  email character varying(255),
  info jsonb,
  CONSTRAINT person_pkey PRIMARY KEY (id)
)
WITH (
  OIDS=FALSE
);

Incovenients

The main inconvenient in using JSON fields seen in this project is that the json fields can not be queried (at least when using hibernate as JPA provider) via JPQL queries. The support of Postgres for JSON fields being considered specific (most of the other database engines don't deal with JSON/JSONB fields) lead to not having introduced direct support for it in JPA.

This PoC there should give an idea on how to store generic data in a single table by using JSON fields, but it seems clear that, in order to query the data, native (Postgres specific) SQL should be used.

Similar projects

• https://github.com/brant-hwang/springboot-postgresql94-hibernate5-example.git
• https://github.com/sasa7812/psql-cache-evict-POC.git

psql-cache-evict-POC project (via eclipselink JPA provider) offers the possibility to execute queries related to JSON fields :

        String jpql = "SELECT c FROM Course c where SQL('course_mapped ->> ''?'' = ''Second one''',c.name) ";

On the other hand, hibernate JPA provider doesn't support such constructs.

Environment requirements

• Java 8
• Spring Boot 1.3.2.RELEASE
• Hibernate 5.0.2
• PostgreSQL 9.4
• Maven 3