问题
Maybe I got it wrong but i though that JPA was able to update an existing table (model changed adding a column) but is not working in my case.
I can see in the logs eclipselink attempting to create it but failing because it already exists. Instead of trying an update to add the column it keeps going.
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/jwrestling"/>
<property name="javax.persistence.jdbc.password" value="password"/>
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
<property name="javax.persistence.jdbc.user" value="user"/>
<property name="eclipselink.ddl-generation" value="create-tables"/>
<property name="eclipselink.logging.logger" value="org.eclipse.persistence.logging.DefaultSessionLog"/>
<property name="eclipselink.logging.level" value="INFO"/>
And here's the table with the change (online column added)
[EL Warning]: 2010-05-31 14:39:06.044--ServerSession(16053322)--Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.1.0.v20100517-r7246): org.eclipse.persistence.exceptions.DatabaseException Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Table 'account' already exists Error Code: 1050 Call: CREATE TABLE account (ID INTEGER NOT NULL, USERNAME VARCHAR(32) NOT NULL, SECURITY_KEY VARCHAR(255) NOT NULL, EMAIL VARCHAR(64) NOT NULL, STATUS VARCHAR(8) NOT NULL, TIMEDATE DATETIME NOT NULL, PASSWORD VARCHAR(255) NOT NULL, ONLINE TINYINT(1) default 0 NOT NULL, PRIMARY KEY (ID)) Query: DataModifyQuery(sql="CREATE TABLE account (ID INTEGER NOT NULL, USERNAME VARCHAR(32) NOT NULL, SECURITY_KEY VARCHAR(255) NOT NULL, EMAIL VARCHAR(64) NOT NULL, STATUS VARCHAR(8) NOT NULL, TIMEDATE DATETIME NOT NULL, PASSWORD VARCHAR(255) NOT NULL, ONLINE TINYINT(1) default 0 NOT NULL, PRIMARY KEY (ID))") [EL Warning]: 2010-05-31 14:39:06.074--ServerSession(16053322)--Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.1.0.v20100517-r7246): org.eclipse.persistence.exceptions.DatabaseException
After this it continues with the following.
Am I doing something wrong or is a bug?
回答1:
As of EclipseLink 2.4, you can use this in the specification of your persistence unit:
<property name="eclipselink.ddl-generation" value="create-or-extend-tables" />
回答2:
This is the expected behavior when using the create-tables value. From the documentation about the eclipselink.ddl-generation property:
Using EclipseLink JPA Extensions for Schema Generation
The following are the valid values for the use in a
persistence.xmlfile:
none– EclipseLink does not generate DDL; no schema is generated.create-tables– EclipseLink will attempt to execute aCREATE TABLESQL for each table. If the table already exists, EclipseLink will follow the default behavior of your specific database and JDBC driver combination (when aCREATE TABLESQL is issued for an already existing table). In most cases an exception is thrown and the table is not created. EclipseLink will then continue with the next statement. (See also eclipselink.create-ddl-jdbc-file-name.)drop-and-create-tables– EclipseLink will attempt toDROPall tables, thenCREATEall tables. If any issues are encountered, EclipseLink will follow the default behavior of your specific database and JDBC driver combination, then continue with the next statement. (See also eclipselink.create-ddl-jdbc-file-name and eclipselink.drop-ddl-jdbc-file-name.)
So you might want drop-and-create-tables instead.
回答3:
Hibernate JPA implementation does exactly what you want. Here is the property that enables that behaviour:
property name="hibernate.hbm2ddl.auto" value="update"
回答4:
create-or-extend-tables does the trick
来源：https://stackoverflow.com/questions/2945714/eclipselink-update-existing-tables