Custom Key Generator In Hibernate
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
.
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Define the cache key at the class and method level. You can define the cache key at class and method level with the key and keyGenerator attributes of the @Cachable, @CachePut and @CacheEvict annotations. If key and keyGenerator are empty (by default), Spring Cache will use the SimpleKeyGenerator if no custom key generator implementations have. Jun 13, 2016 The custom identifier generator. We need a Hibernate identifier generator that can take any value that we manually assign, and it can also automatically generate a unique identifier when the entity identifier is null. However, the user does not want to use a UUID-like random identifier.
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
Nba 2k17 activation key generator. 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.
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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
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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.
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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.
Example Project
Custom Key Generator In Hibernate Windows 7
Dependencies and Technologies Used:
Custom Key Generator In Hibernate Key
- h2 1.4.193: H2 Database Engine.
- hibernate-core 5.2.8.Final: The core O/RM functionality as provided by Hibernate.
Implements javax.persistence:javax.persistence-api version 2.1 - JDK 1.8
- Maven 3.3.9