Hibernate MySQL方言配置遇到的坑

环境 hibernate5.2.17、MySQL5.5，采用JPA注解配置

1. The First

配置文件：peresistence.xml

//...其它略...
<property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
<property name="hibernate.show_sql" value="true" />
<property name="hibernate.format_sql" value="true" />
<property name="hibernate.hbm2ddl.auto" value="create" /> 

运行TestApp，报了异常

异常：

2018-09-15 15:46:06 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
...略....
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'type=MyISAM' at line 21

原因：
  MyISAM引擎不支持外键，创建不了表并报错 。
  MySQLDialect是MySQL5.X之前的版本,其默认的引擎是MyISAM。部分源码如下：

private MySQLStorageEngine storageEngine;


//org.hibernate.dialect.MySQLDialect.getDefaultMySQLStorageEngine()
protected MySQLStorageEngine getDefaultMySQLStorageEngine() {
        return MyISAMStorageEngine.INSTANCE;
}

//org.hibernate.dialect.MyISAMStorageEngine.getTableTypeString(String)
@Override
public String getTableTypeString(String engineKeyword) {
    return String.format( " %s=MyISAM", engineKeyword );
}

所以更改配置

<property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/>

---

2. The second

  改为上面的配置后，运行，未报异常，表创建成功。

表如下：

等等，外键呢 ？？！？？
 去控制台查看sql

  发现存储引擎还是 engine=MyISAM ，于是又去查看 MySQL5Dialect 的源码。

//org.hibernate.dialect.MySQL5Dialect
public class MySQL5Dialect extends MySQLDialect{}

  MySQL5Dialect 继承自 MySQLDialect，发现其源码中并没有更改默认存储引擎，
所以然是 MyISAM。但是MySQL5Dialect并没有报异常，能够创建表。

PS：在Navicat中手动添加外键，选择外键的时候有如下提示：

点击保存外键，然后外键消失。这时候就要注意存储引擎了。

3. The third

改为如下配置：

<property name="hibernate.dialect" value="org.hibernate.dialect.MySQL55Dialect"/>

这次OK了。其源码如下，继承自 MySQL5Dialect ，但 以看到改用了InnoDB存储引擎。

//org.hibernate.dialect.MySQL55Dialect
public class MySQL55Dialect extends MySQL5Dialect {

    @Override
    protected MySQLStorageEngine getDefaultMySQLStorageEngine() {
        return InnoDBStorageEngine.INSTANCE;
    }
}

//org.hibernate.dialect.InnoDBStorageEngine
public class InnoDBStorageEngine implements MySQLStorageEngine{

    public static final MySQLStorageEngine INSTANCE = new InnoDBStorageEngine();

    @Override
    public String getTableTypeString(String engineKeyword) {
        return String.format( " %s=InnoDB", engineKeyword );
    }   
}

如下也行。

<property name="hibernate.dialect" value="org.hibernate.dialect.MySQL57Dialect"/>
//MySQL57Dialect继承自MySQL55Dialect，添加了一些新的数据格式。
//org.hibernate.dialect.MySQL57Dialect
public class MySQL57Dialect extends MySQL55Dialect {}


<property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect"/>
// MySQL5InnoDBDialect。已弃用，所以不推荐。
/** A Dialect for MySQL 5 using InnoDB engine
 *
 * @author Gavin King,
 * @author Scott Marlow
 * @deprecated Use "hibernate.dialect.storage_engine=innodb" environment variable or JVM system property instead.
 */
@Deprecated
public class MySQL5InnoDBDialect extends MySQL5Dialect {

    @Override
    protected MySQLStorageEngine getDefaultMySQLStorageEngine() {
        return InnoDBStorageEngine.INSTANCE;
    }
}

但是使用如下方言，又双叒叕报错了，创建不了表并报错。

org.hibernate.dialect.MySQLInnoDBDialect

源码如下，继承自MySQLDialect ，又弃用了，但是它设置了InnDB存储引擎 。为什么报错 ？？？这个坑没爬上来，求指点。

/**
 * A Dialect for MySQL using InnoDB engine
 *
 * @author Gavin King
 * @deprecated Use "hibernate.dialect.storage_engine=innodb" environment variable or JVM system property instead.
 */
@Deprecated
public class MySQLInnoDBDialect extends MySQLDialect {

    @Override
    protected MySQLStorageEngine getDefaultMySQLStorageEngine() {
        return InnoDBStorageEngine.INSTANCE;
    }
}

---

附：

TestApp

public class TestApp{
    @Test
    public void  testDialect(){
        EntityManagerFactory entityManagerFactory = HbnUtil.getEntityManager(); 
    }
}

Entity

Entity
@Table(name = "Metar")
@DynamicInsert
public class Metar {

    @Id
    @GenericGenerator(name = "uuid", strategy = "uuid")
    @GeneratedValue(generator = "uuid")
    private String mid;
    ....略...

    @OneToMany(targetEntity = SkyCondition.class, mappedBy = "metar", fetch = FetchType.EAGER,cascade=CascadeType.ALL)
    private Set<SkyCondition> skyConditionsSet;

    ....略setter/getter...
}


@Entity
@Table(name = "sky_condition")
public class SkyCondition {

    @Id
    @GenericGenerator(name = "uuid", strategy = "uuid")
    @GeneratedValue(generator = "uuid")
    private String skyId;

    @ManyToOne(targetEntity = Metar.class, fetch = FetchType.EAGER)
    @JoinColumn(name = "metar_id",referencedColumnName="mid")
    private Metar metar;

}

---

参考：
MySQL存储引擎中的MyISAM和InnoDB区别详解

Hibernate的dialect 方言大全