Custom Key Generator In Hibernate

Posted on 17.12.202022.08.2017by admin

Jan 10, 2019 Premiered Jan 10, 2019 Today I will show you how you can Implement a Custom, Sequence-Based ID Generator with #Hibernate. A lot of applications use primary keys that are based on a sequence but use. Understanding Hibernate element In this lesson you will learn about hibernate generator method in detail. Hibernate generator element generates the primary key for new record. There are many options provided by the generator method to be used in different situations. The generator element. This is the optional element under. Mar 21, 2020 Hibernate maintains the mapping of all in-built basic types in the BasicTypeRegistry. Thus, eliminating the need to annotate mapping information for such types. Additionally, Hibernate allows us to register custom types, just like basic types, in the BasicTypeRegistry. At my company we've been working in a large project using Hibernate 2.x. And we use massive custom ID generators. But I've found (too late) that custom ID generator often isn't a good Idea, at least in our project. Why not use a SEQUENCE or an IDENTITY column? It's easy to maintain and you can use in multiple servers. Jun 26, 2011 The thing is, while saving an object into the database, the generator informs to the hibernate that, how the primary key value for the new record is going to generate; hibernate using different primary key generator algorithms, for each algorithm internally a class is created by hibernate for its implementation. Dec 15, 2016 This article shows you how to define custom annotations for attributes in generated hibernate source code. To define custom annotation for hibernate code generation: Right click on the association role (which eventually will become an attribute) and select Owned By target class.

Every JPA entity is required to have a field which maps to primary key of the database table. Such field must be annotated with @Id.

Simple vs Composite primary keys

A simple primary key consists of a single Java field which maps to a single table column.
A composite primary key consists of multiple Java fields which individually map to separate columns.

Supported types for a primary key

A simple primary key field or one of the composite primary key field should be one of the following types:

Any Java primitive type
any Any primitive wrapper type
java.lang.String
java.util.Date
java.sql.Date
java.math.BigDecimal
java.math.BigInteger

In this tutorial we are going to focus on generation strategies of simple primary key.

@GeneratedValue Annotation

This annotation defines the types of primary key generation strategies. If this annotation is not used then application is responsible to populate and manage @Id field values itself.

Windows anytime upgrade key generator 2013. The use of the GeneratedValue annotation is only required to be supported for simple primary keys.

GenerationType enum defines four strategies: Generation Type . TABLE, Generation Type. SEQUENCE, Generation Type. IDENTITY and Generation Type. AUTO. Let's understand them with examples.

GenerationType.SEQUENCE

With this strategy, underlying persistence provider must use a database sequence to get the next unique primary key for the entities.

We have created the following Util class to reuse the code for other examples.

Also, in the persistence.xml, we have created four persistence-unit, so that we can try four GenerationType independently. We are using Hibernate as persistence provider.

Let's create main class to try out Entity1 key generation.

Output

Above output shows one table MYENTITY1 and one sequence HIBERNATE_SEQUENCE are created.

GenerationType.TABLE

With this strategy, underlying persistence provider must use a database table to generate/keep the next unique primary key for the entities.

Output

This time no sequence is generated, instead an additional table named 'HIBERNATE_SEQUENCES' is created to maintain primary key sequence.

GenerationType.IDENTITY

This GenerationType indicates that the persistence provider must assign primary keys for the entity using a database identity column. IDENTITY column is typically used in SQL Server. This special type column is populated internally by the table itself without using a separate sequence. If underlying database doesn't support IDENTITY column or some similar variant then the persistence provider can choose an alternative appropriate strategy. In this examples we are using H2 database which doesn't support IDENTITY column.

Output

Above output shows that a sequence is used for primary keys.

GenerationType.AUTO

This GenerationType indicates that the persistence provider should automatically pick an appropriate strategy for the particular database. This is the default GenerationType, i.e. if we just use @GeneratedValue annotation then this value of GenerationType will be used.

Output

Above output shows that a sequence is used for primary keys.

When @GeneratedValue not used

If we don't use @GeneratedValue annotation at all, then we have to populate the unique primary keys ourselves. In this example, we are simply assigning it to the value returned from System.nanoTime()

Output

Above output shows that a no sequence or extra table were generated.