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[转载]hibernate.hbm2ddl.auto—Hibernate自动建表的配置_ETHAN_新浪博客
[转载]hibernate.hbm2ddl.auto—Hibernate自动建表的配置_ETHAN_新浪博客
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I really want to know more about the update, export and the values that could be given to hibernate.hbm2ddl.auto
I need to know when to use the update and when not? And what is the alternative?
These are changes that could happen over DB:
New tables
new columns in old tables
columns deleted
data type of a column changed
a type of a column changed it attributes
tables have been dropped
values of a column has changed
In each case what is the best solution?
From the :
hibernate.hbm2ddl.auto
Automatically validates or exports schema DDL to the database when the SessionFactory is created. With create-drop, the database schema will be dropped when the SessionFactory is closed explicitly.
e.g. validate | update | create | create-drop
So the list of possible options are,
validate: validate the schema, makes no changes to the database.
update: update the schema.
create: creates the schema, destroying previous data.
create-drop: drop the schema at the end of the session.
These options seem intended to be developers tools and not to facilitate any production level databases, you may want to have a look at th
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The configuration property is called hibernate.hbm2ddl.auto
In our development environment we set hibernate.hbm2ddl.auto=create-drop to drop and create a clean database each time we deploy, so that our database is in a known state.
In theory, you can set hibernate.hbm2ddl.auto=update to update your database with changes to your model, but I would not trust that on a production database. An earlier version of the documentation said that this was experimental, I do not know the current status.
Therefore, for our production database, do not set hibernate.hbm2ddl.auto - the default is to make no database changes. Instead, we manually create an SQL DDL update script that applies changes from one version to the next.
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There's also the undocumented value of "none" to disable it entirely.
I would use
for updating your db. hibernate's schema update feature is really only o.k. for a developer while they are developing new features. In a production situation, the db upgrade needs to be handled more carefully.
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If you don't want to use Strings in your app and are looking for predefined constants have a look at org.hibernate.cfg.AvailableSettings class included in the Hibernate JAR, where you'll find a constant for all possible settings. In your case for example:
* Auto export/update schema using hbm2ddl tool. Valid values are &tt&update&/tt&,
* &tt&create&/tt&, &tt&create-drop&/tt& and &tt&validate&/tt&.
String HBM2DDL_AUTO = "hibernate.hbm2ddl.auto";
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I dedicated a
for the most common Hibernate DDL generation strategies:
The hibernate.hbm2ddl.auto="update" is convenient but less flexible if you plan on adding functions or executing some custom scripts.
The most flexible approach is to generate the DDL scripts with org.hibernate.tool.ant.HibernateToolTask and then use a component to execute the scripts on context startup. The destroy scripts are called when the Spring context is closed.
The second approach is much more flexible, especially if you want to mix .
Needless to say that this is only an Integration testing concern, since for production environment we use .
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I Think you should have to concentrate on the
SchemaExport Class
this Class Makes Your Configuration Dynamic
So it allows you to choose whatever suites you best...
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if you want to use hibernate.hbm2ddl.auto it's good if you remove this attribute. In large System, developer always prefer not to use that is
"don't use hibernate.hbm2ddl.auto in you application. just remove this from xml"
it will use default hbm2ddl
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& 综合 & 正文
hibernate.hbm2ddl.auto 的设置
&?xml version='1.0' encoding='UTF-8'?&
&!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"&
&!-- Generated by MyEclipse Hibernate Tools.
&hibernate-configuration&
&session-factory&
&property name="connection.username"&root&/property&
&property name="connection.url"&
jdbc:mysql://localhost:3306/myhibernate
&/property&
&property name="dialect"&
org.hibernate.dialect.MySQLDialect
&/property&
&property name="connection.driver_class"&
com.mysql.jdbc.Driver
&/property&
&property name="hbm2ddl.auto"&create&/property&
&property name="c3p0.min_size"&5&/property&
&property name="c3p0.max_size"&20&/property&
&property name="c3p0.timeout"&300&/property&
&property name="c3p0.max_statements"&50&/property&
&property name="c3p0.idle_test_period"&3000&/property&
&property name="show_sql"&true&/property&
&property name="format_sql"&true&/property&
&property name="myeclipse.connection.profile"&mysql&/property&
&property name="connection.password"&&/property&
&mapping resource="hello/Message.hbm.xml" /&
&/session-factory&
&/hibernate-configuration&
加载hibernate时，验证创建数据库表结构create
每次加载hibernate，重新创建数据库表结构，这就是导致数据库表数据丢失的原因。create-drop
加载hibernate时创建，退出是删除表结构update
加载hibernate自动更新数据库结构在本机开发调试初始化数据的时候可以选择create、update等。但是网站发布正式版本的时候，对数据库现有的数据或表结构进行自动的更新是很危险的。此时此刻应该由DBA同志通过手工的方式进行后台的数据库操作。hibernate.hbm2ddl.auto的值建议是“none”或“validate”。“validate”应该是最好的选择：这样 spring在加载之初，如果model层和数据库表结构不同，就会报错，这样有助于技术运维预先发现问题。
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