hbm2ddl.auto 设置为“UPDATE”，但它尝试在每次插入之前创建表

Question

如果我错了，请纠正我！
通常，如果 hbm2ddl.auto 设置为“UPDATE”，hibernate 会检查表是否存在于 db 中，如果不存在，则创建该表并推送数据，如果表存在，则将数据添加到该表中。
对于 hbm2ddl.auto = update，我观察到的是，在每次插入之前，hibernate 都在尝试创建表。虽然表存在，但它会在日志中抛出异常，然后休眠知道表的存在。
这是正常行为吗？还是我错过了什么？

请在控制台中找到以下借助 log4j 生成的日志..

Hibernate: create table UsersCC (userID int4 not null, userDOB date, userEmail varchar(255), userPswd varchar(255), primary key (userID))
23:02:27,799  WARN ExceptionHandlerLoggedImpl:27 - GenerationTarget encountered exception accepting command : Error executing DDL via JDBC Statement
org.hibernate.tool.schema.spi.CommandAcceptanceException: Error executing DDL via JDBC Statement
    at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:67)
    at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.applySqlString(AbstractSchemaMigrator.java:524)
    at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.applySqlStrings(AbstractSchemaMigrator.java:470)
    at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.createTable(AbstractSchemaMigrator.java:273)
    at org.hibernate.tool.schema.internal.GroupedSchemaMigratorImpl.performTablesMigration(GroupedSchemaMigratorImpl.java:71)
    at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.performMigration(AbstractSchemaMigrator.java:203)
    at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.doMigration(AbstractSchemaMigrator.java:110)
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.performDatabaseAction(SchemaManagementToolCoordinator.java:183)
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.process(SchemaManagementToolCoordinator.java:72)
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:309)
    at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:445)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:710)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:726)
    at com.hibernate.Setup.SetupTest.main(SetupTest.java:19)
Caused by: org.postgresql.util.PSQLException: ERROR: relation "userscc" already exists
    at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2310)
    at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:2023)
    at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:217)
    at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:421)
    at org.postgresql.jdbc.PgStatement.executeWithFlags(PgStatement.java:318)
    at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:310)
    at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:54)
    ... 13 more
Hibernate: insert into UsersCC (userDOB, userEmail, userPswd, userID) values (?, ?, ?, ?)
23:02:27,998 TRACE BasicBinder:65 - binding parameter [1] as [DATE] - [Sun Jan 01 23:02:25 IST 2017]
23:02:27,999 TRACE BasicBinder:65 - binding parameter [2] as [VARCHAR] - [motogg@support.com]
23:02:28,000 TRACE BasicBinder:65 - binding parameter [3] as [VARCHAR] - [lenovo18]
23:02:28,004 TRACE BasicBinder:65 - binding parameter [4] as [INTEGER] - [101]
23:02:28,013  INFO pooling:230 - HHH10001008: Cleaning up connection pool [jdbc:postgresql://localhost:5432/campusCafeDb]

如果正常，那不是性能问题吗？

Answer 1

hbm2ddl.auto 验证： 如果该值为 validate 则 hibernate 仅验证表和列是否存在。如果表不存在，那么休眠会抛出异常。验证是 hbm2ddl.auto 的默认值。

hbm2ddl.auto 更新： 如果值是更新的，那么休眠检查表和列。如果表不存在，则创建一个新表，如果列不存在，则为其创建新列。

此链接对所有值都有很好的解释。

http://www.onlinetutorialspoint.com/hibernate/hbm2ddl-auto-example-hibernate-xml-config.html

none 我猜是非官方值。我在stackoverflow的某个地方找到了它，但我忘了在哪里。