Nov 26, 2018 To customize the schema generation process, the hibernate.hbm2ddl.import. With Hibernate, you can specify a default value for a. Id foreign key. I believe you need to map it as nullable='true' so that it doesn't automatically create a FK constraint in the DDL. Some Databases support FK creation and some does not, that might be why you see one Database create a FK and one doesn't. Click Next in Hibernate ORM Generation dialog. In the Default Table Generation dialog, select increment strategy for the key generation. A Java Package is required for generating the object model classes. Click the Browse. Button beside Java Package and create a new Java package com.bea.beans using the New Java Package link.

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The <generator> class is a sub-element of id. It is used to generate the unique identifier for the objects of persistent class. There are many generator classes defined in the Hibernate Framework.


All the generator classes implements the org.hibernate.id.IdentifierGenerator interface. The application programmer may create one's own generator classes by implementing the IdentifierGenerator interface. Hibernate framework provides many built-in generator classes:

  1. assigned
  2. increment
  3. sequence
  4. hilo
  5. native
  6. identity
  7. seqhilo
  8. uuid
  9. guid
  10. select
  11. foreign
  12. sequence-identity

1) assigned

It is the default generator strategy if there is no <generator> element . In this case, application assigns the id. For example:

Hibernate Default Foreign Key Generation 10

2) increment

It generates the unique id only if no other process is inserting data into this table. It generates short, int or long type identifier. If a table contains an identifier then the application considers its maximum value else the application consider that the first generated identifier is 1. For each attribute value, the hibernate increment the identifier by 1. Syntax:

3) sequence

It uses the sequence of the database. if there is no sequence defined, it creates a sequence automatically e.g. in case of Oracle database, it creates a sequence named HIBERNATE_SEQUENCE. In case of Oracle, DB2, SAP DB, Postgre SQL or McKoi, it uses sequence but it uses generator in interbase. Syntax:

For defining your own sequence, use the param subelement of generator.

4) hilo

It uses high and low algorithm to generate the id of type short, int and long. Syntax:

5) native

It uses identity, sequence or hilo depending on the database vendor. Syntax:

6) identity

User.generate_otp_secret must specify a key. It is used in Sybase, My SQL, MS SQL Server, DB2 and HypersonicSQL to support the id column. The returned id is of type short, int or long. It is responsibility of database to generate unique identifier.

7) seqhilo

It uses high and low algorithm on the specified sequence name. The returned id is of type short, int or long.

Foreign

8) uuid

It uses 128-bit UUID algorithm to generate the id. The returned id is of type String, unique within a network (because IP is used). The UUID is represented in hexadecimal digits, 32 in length.

9) guid

It uses GUID generated by database of type string. It works on MS SQL Server and MySQL.

10) select

It uses the primary key returned by the database trigger.

11) foreign

It uses the id of another associated object, mostly used with <one-to-one> association.

12) sequence-identity

It uses a special sequence generation strategy. It is supported in Oracle 10g drivers only.
Next TopicDialects In Hibernate

Ranch Hand
posted 10 years agoHibernate
Hello there..
Created 3 JPA annotated classes:
User:

Device:

Token:

Am trying to set up ER relationships in Hibernate 3 / JPA (or even in MySQL 5) like this:
User has one to many Devices.
User.userid (Primary Key)
Device.id (Primary Key)
Device has one to one relationship with Token.
Device.id (Primary Key)
Token.id (Primary Key)
Question(s):
(1) How do I set these up in Hibernate3 or MySQL5 code?
(2) Am very new with SQL so would it be that the Device.id is the foreign key of User.userid and vice versa with Device and Token?
Am very new to Hibernate 3 / JPA so would appreciate it if someone could help..
Thank you and happy programming!
author and cow tipper
posted 10 years agoSo, you'll need instance variables:

User has one to many Devices.


So, the User class will has a List of devices, List devices = new ArrayList(); Put in setters and getters. Device will have an instance of a User. Then add your JPA annotations like usual.

Device has one to one relationship with Token.


Add instance variables - Devices has an instance of a Token, and a Token has an instance of a Device. Then perform the annotation mapping as usual with any one-to-one association.
Here's a good tutorial on mapping one-to-one relations with Hibernate and JPA:
Mapping Associations with the Java Persistence API

Hibernate Default Foreign Key Generation Download

There's a discussion of one-to-many mappings on that site as well.

Mysql Foreign Key Constraint


Keep asking questions, and let us know how you're getting along, including code snippets and any errors you have.
-Cameron McKenzie
Ranch Hand
posted 10 years ago
Cameron,
Yes, I checked out the tutorial and got my code working!
The tutorial does throw an exception however..
Created my tables like this:


Exam:

ExamDetail:

ExamApp:

When you run ExamApp this is what happens:

Question(s):
(1) In the CreateExam.sql query, you stated to place this:
KEY FK2FB81FB83A97F5 (detail_id),
CONSTRAINT FK2FB81FB83A97F5
What is the FK2FB81FB83A97F5 for and where do I create values like this for my own foreign keys?
(2) What is causing the exception?
Thank you for everything!
-James
author and cow tipper
posted 10 years ago
Well, in this case, you just forgot to add the Exam and ExamDetail to the HibernateConfig in the HibernateUtil class:

Creating a HibernateUtil Class
-Cameron McKenzie
Ranch Hand
posted 10 years ago
Cameron,
Thank you for your help! You stated these fields in your tutorial:
KEY FK2FB81FB83A97F5 (detail_id),
CONSTRAINT FK2FB81FB83A97F5
What is the FK2FB81FB83A97F5 for and where do I create values like this for my own foreign keys?
-James
author and cow tipper
posted 10 years ago
Oh, I have no idea what those are. I think it's just the identifier MySQL gives to the foreign key constraint. With the various classes added to the Hibernate Config, you can have Hibernate create your database tables for you.

Creating Tables with the SchemaExport create
-Cameron McKenzie
Ranch Hand
posted 10 years ago
Okay, cool.. Thank you! I've used the SchemaExport mechanism before but still felt safer by creating tables in MySQL by using the scripts.
-James
author and cow tipper
posted 10 years ago

Hibernate Default Foreign Key Generation Download

The nice thing is that the log files actually show you the scripts. In fact, I think if you do create(true,false) or something like that, it spits out the script in the log file, but doesn't actually connect to the database and create the tables, so you can see exactly what SQL, and it is SQL, that Hibernate will use. It's a great feature if you can do a 'top down' database design.
-Cameron McKenzie