Inheritance is one of the key concepts in Java, and most development teams prefer using it in their domain model. Unfortunately, relational table models don’t support the concept of inheritance. The JPA specification defines multiple mapping strategies to bridge the gap between the object-oriented and the relational world. I explained them in great detail in…
DTO projections provide better performance than entities if you only want to read but not change the retrieved information. They avoid the management overhead of an entity class and enable you to only select the database columns your business code needs. But as so often, DTO projections also have a downside, and that’s the handling…
Inheritance is one of the key concepts of all object-oriented programming languages. And Java makes there no difference. All developers are familiar with this concept and expect to use it in all parts of their code. That, of course, also includes the persistence layer and the entity model. But the concept of inheritance doesn’t exist…
Some primary keys consist of more than 1 entity attribute or database column. These are called composite primary keys. They often contain a foreign key reference to a parent object or represent a complex natural key. Another reason to use composite keys is combining a domain-specific value with a simple counter, e.g., an order type…
QueryDSL is a popular framework that provides you a Java API to create queries for relational databases and other data stores. If you’re familiar with JPA’s Criteria API, you might think that it does the same as QueryDSL and that you don’t need to learn about another framework. But I recommend you give QueryDSL a…