Why you should never use the TABLE identifier generator with JPA and Hibernate

Introduction

From a data access perspective, JPA supports two major types of identifiers:

  • assigned
  • generated

The assigned identifiers must be manually set on every given entity prior to being persisted. For this reason, assigned identifiers are suitable for natural keys.

For synthetic Primary Keys, we need to use a generated entity identifier, which is supported by JPA through the use of the @GeneratedValue annotation.

There are four types of generated identifier strategies which are defined by the GenerationType enumeration:

  • AUTO
  • IDENTITY
  • SEQUENCE
  • TABLE

The AUTO identifier generator strategy chooses one of the other three strategies (IDENTITY, SEQUENCE or TABLE) based on the underlying relational database capabilities.

While IDENTITY maps to an auto incremented column (e.g. IDENTITY in SQL Server or AUTO_INCREMENT in MySQL) and SEQUENCE is used for delegating the identifier generation to a database sequence, the TABLE generator has no direct implementation in relational databases.

This post is going to analyze why the TABLE generator is a poor choice for every enterprise application that cares for performance and scalability.

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How to map table rows to columns using SQL PIVOT or CASE expressions

Introduction

I’m now reading the wonderful SQL Antipatterns book by Bill Karwin. The book is a great reference for any developer that needs to interact with a Relational Database System.

In this book, the Entity-Attribute-Value (EAV) model is portrayed as an Anti-Pattern. Although I must admit that a proper relational schema is almost always the best approach when designing an enterprise system, there are use cases when the EAV model is justified.

In this post, I’m going to explain when to use EAV and how to transpose a ResultSet so that rows become columns.

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The performance penalty of Class.forName when parsing JPQL and Criteria queries

Introduction

While reviewing this Hibernate Pull Request, I stumbled on the HHH-10746 Jira issue. After doing some research, I realized that this issue was reported multiple times in the past 10 years:

In this post, I’m going to explain why this issue was causing performance issues, and how it got fixed.

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How to customize an entity association JOIN ON clause with Hibernate @JoinFormula

Introduction

As I explained in this previous article, you can map calculated properties using Hibernate @Formula, and the value is generated at query time.

In this post, you’ll see how you can use a custom SQL fragment to customize the JOIN relationship between two entities, or an entity and a collection of embeddable types.

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