Hibernate中的NamingStrategy

   项目中表名称的统一命名使用的了NamingStrategy的命名策略。

在Java对象里面, 偶们知道一个良好的命名规范会采用大写单词的首字母, 比如订单项这个对象, 偶们会起名为OrderItem, 这样很容易就看出来这个对象是由Order和Item 2个单词组成的, 断词就很容易了, 而属性也是如此, 比如maxPrice, totalPrice等等.

但是如果按照同样的命名规范运到数据库的时候, 由于很多数据库对于表名, 字段名是大小写不敏感的, 所以最常见的策略是加下划线作为断词的依据:
OrderItem -> order_item
maxPrice -> max_price

这样运用Hibernate的时候, 偶们就得手工在mapping文件里面指明:
<class name="OrderItem" table="order_item">
<property name="maxPrice" column="max_price"/>

 

 

NamingStrategy的源代码如下：

 

public interface NamingStrategy {
 /**

 * 返回实体的表名
  * Return a table name for an entity class
  * @param className the fully-qualified class name  参数为类的完整名称的
  * @return a table name
  */
 public String classToTableName(String className);
 /**将一个属性映射为一个表的列明地方法
  * Return a column name for a property path expression
  * @param propertyName a property path
  * @return a column name
  */
 public String propertyToColumnName(String propertyName);
 /**根据表名获取的映射文件名称
  * Alter the table name given in the mapping document
  * @param tableName a table name
  * @return a table name
  */
 public String tableName(String tableName);
 /**
  * Alter the column name given in the mapping document
  * @param columnName a column name
  * @return a column name
  */
 public String columnName(String columnName);
 /**返回相关联的表名称
  * Return a collection table name ie an association having a join table
  *
  * @param ownerEntity
  * @param ownerEntityTable owner side table name
  * @param associatedEntity
  * @param associatedEntityTable reverse side table name if any
  * @param propertyName collection role
  */
 public String collectionTableName(
   String ownerEntity, String ownerEntityTable, String associatedEntity, String associatedEntityTable,
   String propertyName
 );
 /**
  * Return the join key column name ie a FK column used in a JOINED strategy or for a secondary table
  *
  * @param joinedColumn joined column name (logical one) used to join with
  * @param joinedTable joined table name (ie the referenced table) used to join with
  */
 public String joinKeyColumnName(String joinedColumn, String joinedTable);
 /**
  * Return the foreign key column name for the given parameters
  * @param propertyName the property name involved
  * @param propertyEntityName
  * @param propertyTableName the property table name involved (logical one)
  * @param referencedColumnName the referenced column name involved (logical one)
  */
 public String foreignKeyColumnName(
   String propertyName, String propertyEntityName, String propertyTableName, String referencedColumnName
 );
 /**
  * Return the logical column name used to refer to a column in the metadata
  * (like index, unique constraints etc)
  * A full bijection is required between logicalNames and physical ones
  * logicalName have to be case insersitively unique for a given table
  *
  * @param columnName given column name if any
  * @param propertyName property name of this column
  */
 public String logicalColumnName(String columnName, String propertyName);
 /**
  * Returns the logical collection table name used to refer to a table in the mapping metadata
  *
  * @param tableName the metadata explicit name
  * @param ownerEntityTable owner table entity table name (logical one)
  * @param associatedEntityTable reverse side table name if any (logical one)
  * @param propertyName collection role
  */
 public String logicalCollectionTableName(String tableName, String ownerEntityTable, String associatedEntityTable, String propertyName);

 /**
  * Returns the logical foreign key column name used to refer to this column in the mapping metadata
  *
  * @param columnName given column name in the metadata if any
  * @param propertyName property name
  * @param referencedColumn referenced column name (logical one) in the join
  */
 public String logicalCollectionColumnName(String columnName, String propertyName, String referencedColumn);
}

 

 

源码如上必须注意的方法：

classToTableName：将一个类转换为表名

propertyToColumnName：属性转换为列名

tableName：根据表名返回映射文件

columnName：根据列名返回映射列名；

 

在初始化配置的时候, 把这个NamingStrategy加上:

 Configuration config = new Configuration();;  
 config.setNamingStrategy(UnderscoreNamingStrategy.INSTANCE);;

这样mapping文件就变得简单多了:

<class name="OrderItem">
<property name="maxPrice"/>

NamingStrategy还可以用在其他方面, 比如有些数据库设计规范统一要求Table前面加上模块名称 (如, 属于Order模块的统一加上ORDER_ ), 比如还有些恶心规范统一要求表名和字段名采用4码缩写 (如, OrderItem -> orde_item, maxPrice -> max_pric), 这些都是NamingStrategy可以解决的脏活累活.