JPA和toplink创建表是否不存在? [英] JPA and toplink create-table on if they don't already exist?

问题描述

看起来jpa会让我问很多问题.

Looks like jpa is something which makes me ask a lot of questions.

已添加此

<property name="toplink.ddl-generation" value="create-tables"/>

我的JPA应用程序始终在运行时创建表，如果表已经存在，则会导致异常.我希望JPA检查表是否已经存在，如果不创建表，但是我找不到上面可以执行此操作的属性的值.

my JPA application always creates tables when running, which results in exceptions in case the tables already exist. I would like JPA to check if the tables already exist and if not create them, however I could not find a value for the property above which does this.

因此，如果我只是将其关闭，是否有办法在某个时候手动告诉JPA创建所有表?

So if I just turn it off, is there a way to tell JPA manually at some point to create all the tables?

更新，这是我得到的异常

Update here's the exception I get

Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Table 'tags' already exists
Error Code: 1050
Call: CREATE TABLE tags (ID BIGINT AUTO_INCREMENT NOT NULL, NAME VARCHAR(255), OCCURRENCE INTEGER, PRIMARY KEY (ID))

MySQLSyntaxErrorException ?!现在肯定是错误的

MySQLSyntaxErrorException?! Now that's wrong for sure

推荐答案

根据

According to http://www.oracle.com/technology/products/ias/toplink/JPA/essentials/toplink-jpa-extensions.html#Java2DBSchemaGen toplink does not have an option to update exiting tables, I'm not sure if I would trust it to do the right thing anyway. You could configure toplink to generate a sql script that you then would have to execute manually to create all tables. The filenames and location can be configured like this:

<property name="toplink.ddl-generation" value="create-tables"/>
<property name="toplink.ddl-generation.output-mode" value="sql-script"/>
<property name="toplink.create-ddl-jdbc-file-name" value="createDDL.sql"/>
<property name="toplink.drop-ddl-jdbc-file-name" value="dropDDL.sql"/>
<property name="toplink.application-location" value="/tmp"/>

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