mybatis 處理枚舉類型

MyBatis支持持久化enum類型屬性。假設t_user表中有一列gender（性別）類型為 varchar2(10)，存儲 MALE 或者 FEMALE 兩種值。並且，User對象有一個enum類型的gender 屬性，如下所示：

public enum Gender { 
MALE,FEMALE; 
}

 

默認情況下MyBatis使用EnumTypeHandler來處理enum類型的Java屬性，並且將其存儲為enum值的名稱。我們不需要為此做任何額外的配置。可以像使用基本數據類型屬性一樣使用enum類型屬性，如下：

create table t_user(
          id number primary key,
          name varchar2(50),
          gender varchar2(10)
);

 

public class User{ 
            private Integer id; 
            private String name; 
            private Gender gender; 

            //setters and getters 
} 

 映射文件：

<insert id="insertUser" parameterType="User"> 
    <selectKey keyProperty="id" resultType="int" order="BEFORE">
        select my_seq.nextval from dual
    </selectKey>
    insert into t_user(id,name,gender) 
    values(#{id},#{name},#{gender}) 
</insert>

映射接口：

public interface XxxxMapper{
    int insertUser(User user);    
}

測試方法：

@Test
public void test_insertUser(){

SqlSession sqlSession = null;
try {
sqlSession = MyBatisSqlSessionFactory.openSession();

SpecialMapper mapper = sqlSession.getMapper(SpecialMapper.class);
User user = new User("tom",Gender.MALE);

mapper.insertUser(user);

sqlSession.commit();
} catch (Exception e) {
e.printStackTrace();
}
}

 

當執行insertStudent語句的時候MyBatis會取Gender枚舉（FEMALE/MALE）的名稱，存儲到GENDER列中。

如果你想存儲FEMALE為0，MALE為1到gender列中，需要在mybatis-config.xml文件中配置專門的類型處理器，並指定它處理的枚舉類型是哪個。
<typeHandler handler="org.apache.ibatis.type.EnumOrdinalTypeHandler" javaType="com.briup.special.Gender"/>

EnumOrdinalTypeHandler這是個類型處理器，源碼中有個set方法就是在幫助我們存值，源碼如下

/**
 *    Copyright 2009-2017 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.type;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

/**
 * @author Clinton Begin
 */
public class EnumOrdinalTypeHandler<E extends Enum<E>> extends BaseTypeHandler<E> {

  private final Class<E> type;
  private final E[] enums;

  public EnumOrdinalTypeHandler(Class<E> type) {
    if (type == null) {
      throw new IllegalArgumentException("Type argument cannot be null");
    }
    this.type = type;
    this.enums = type.getEnumConstants();
    if (this.enums == null) {
      throw new IllegalArgumentException(type.getSimpleName() + " does not represent an enum type.");
    }
  }

  @Override
  public void setNonNullParameter(PreparedStatement ps, int i, E parameter, JdbcType jdbcType) throws SQLException {
    ps.setInt(i, parameter.ordinal());
  }

  @Override
  public E getNullableResult(ResultSet rs, String columnName) throws SQLException {
    int i = rs.getInt(columnName);
    if (rs.wasNull()) {
      return null;
    } else {
      try {
        return enums[i];
      } catch (Exception ex) {
        throw new IllegalArgumentException("Cannot convert " + i + " to " + type.getSimpleName() + " by ordinal value.", ex);
      }
    }
  }

  @Override
  public E getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
    int i = rs.getInt(columnIndex);
    if (rs.wasNull()) {
      return null;
    } else {
      try {
        return enums[i];
      } catch (Exception ex) {
        throw new IllegalArgumentException("Cannot convert " + i + " to " + type.getSimpleName() + " by ordinal value.", ex);
      }
    }
  }

  @Override
  public E getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
    int i = cs.getInt(columnIndex);
    if (cs.wasNull()) {
      return null;
    } else {
      try {
        return enums[i];
      } catch (Exception ex) {
        throw new IllegalArgumentException("Cannot convert " + i + " to " + type.getSimpleName() + " by ordinal value.", ex);
      }
    }
  }
  
}

枚舉類型的【順序值】是根據enum中的聲明順序賦值的。如果改變了Gender里面對象的聲明順序，則數據庫存儲的數據和此順序值就不匹配了。