轻量级封装DbUtils&Mybatis之四MyBatis主键

MyBatis主键#

不支持对象列表存储时对自增id字段的赋值(至少包括3.2.6和3.3.0版本)，如果id不是采用底层DB自增主键赋值，不必考虑此问题
温馨提示：分布式DB环境下，DB主键一般会采用统一的Id生成器生成Id，因此不必考虑由数据库自增策略填充主键值。

解决方案#

参考源码##

1）mybatis-batch-insert项目，请为原作者点赞，支持他开源。
备注：实际代码有少量修改，会在下文列出，本文依据实现方案代码细节反推分析源码处理逻辑过程

批量插入对象列表自增主键赋值分析##

1）在获取数据库返回的主键值后填充到中间存储结构。
2）在构造具体返回对象结构过程中(其实insert语句并不需要)，从中间存储结构将多个主键值填充到具体的对象实例当中。

备注：实际上这种解决方案还是来源于代码分析的结果，接下来简单列述Mybatis主键处理的核心代码及配置

MyBatis处理主键处理流程#

备注：主键填充的处理方法实际是populateKeys。

代码呈上#

测试示例

package org.wit.ff.jdbc;

import org.junit.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.AbstractJUnit4SpringContextTests;
import org.wit.ff.jdbc.dao.HomeTownDao;
import org.wit.ff.jdbc.id.BatchInsertEntities;
import org.wit.ff.jdbc.model.HomeTown;
import org.wit.ff.jdbc.query.Criteria;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by F.Fang on 2015/11/17.
 * Version :2015/11/17
 */
@ContextConfiguration(locations = {"classpath:applicationContext-batch.xml"})
public class HomeTownDaoBatchTest extends AbstractJUnit4SpringContextTests {

    @Autowired
    private HomeTownDao homeTownDao;

    @Test
    public void testBatchInsert(){
        HomeTown ht1 = new HomeTown();
        ht1.setName("hb");
        ht1.setLocation("hubei");
        HomeTown ht2 = new HomeTown();
        ht2.setName("js");
        ht2.setLocation("jiangsu");

        List<HomeTown> list = new ArrayList<>();
        list.add(ht1);
        list.add(ht2);

        BatchInsertEntities<HomeTown> batchEntities = new BatchInsertEntities<>(list);

        homeTownDao.batchInsert(batchEntities);
        System.out.println(batchEntities.getEntities());
    }

}

控制台输出

[3,hb,hubei, 4,js,jiangsu]

模型HomeTown

package org.wit.ff.jdbc.model;

import org.apache.commons.lang3.builder.ReflectionToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;
import org.wit.ff.jdbc.id.IdGenerator;

/**
 * Created by F.Fang on 2015/11/17.
 * Version :2015/11/17
 */
public class HomeTown implements IdGenerator {
    private int id;

    private String name;

    private String location;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public String toString() {
        return ReflectionToStringBuilder.toString(this, ToStringStyle.SIMPLE_STYLE);
    }

    @Override
    public void parseGenKey(Object[] value) {
        if(value!=null && value.length == 1){
            this.id = Integer.valueOf(value[0].toString());
        }
    }
}

HomeTownDao

package org.wit.ff.jdbc.dao;

import org.wit.ff.jdbc.id.BatchInsertEntities;
import org.wit.ff.jdbc.model.HomeTown;

import java.util.List;

/**
 * Created by F.Fang on 2015/11/17.
 * Version :2015/11/17
 */
public interface HomeTownDao {

    void batchInsert(BatchInsertEntities<HomeTown> batchEntities);
}

Mapper配置文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.wit.ff.jdbc.dao.HomeTownDao">

    <insert id="batchInsert" parameterType="org.wit.ff.jdbc.id.BatchInsertEntities" useGeneratedKeys="true" keyProperty="id"
        keyColumn="ID">

        insert into hometown
        (name,location)
        values
        <foreach item="item" collection="entities" separator=",">
            ( #{item.name},#{item.location})
        </foreach>
    </insert>

</mapper>

Spring配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:mybatis="http://mybatis.org/schema/mybatis-spring"
       xsi:schemaLocation="
     http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
     http://mybatis.org/schema/mybatis-spring http://mybatis.org/schema/mybatis-spring.xsd">

    <!-- 数据源 -->
    <bean id="dataSource"
          class="org.apache.commons.dbcp.BasicDataSource"
          destroy-method="close">
        <property name="driverClassName" value="${db.driverClass}"/>
        <property name="url" value="${db.jdbcUrl}"/>
        <property name="username" value="${db.user}"/>
        <property name="password" value="${db.password}"/>
    </bean>

    <!-- 配置 SqlSessionFactory -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"/>
        <!-- 制定路径自动加载mapper配置文件 -->
        <property name="mapperLocations" value="classpath:mappers/*Dao.xml"/>

        <!-- 配置myibatis的settings http://mybatis.github.io/mybatis-3/zh/configuration.html#settings -->
        <property name="configurationProperties">
            <props>
                <prop key="cacheEnabled">true</prop>
            </props>
        </property>

        <property name="typeHandlers">
            <list>
                <bean class="org.wit.ff.jdbc.id.BatchInsertEntitiesTypeHandler"/>
            </list>
        </property>

        <property name="objectWrapperFactory" ref="batchObjectWrapperFactory"/>

        <!-- 类型别名是为 Java 类型命名一个短的名字。 它只和 XML 配置有关, 只用来减少类完全 限定名的多余部分 -->
        <property name="typeAliasesPackage" value="org.wit.ff.jdbc.model"/>

    </bean>

    <bean id="batchObjectWrapperFactory" class="org.wit.ff.jdbc.id.BatchInsertObjectWrapperFactory"/>

    <mybatis:scan base-package="org.wit.ff.jdbc.dao"/>

</beans>

存储主键值的结构

package org.wit.ff.jdbc.id;

import java.util.List;

public class BatchInsertEntityPrimaryKeys {
    private final List<String> primaryKeys;

    public BatchInsertEntityPrimaryKeys(List<String> pks) {
        this.primaryKeys = pks;
    }

    public List<String> getPrimaryKeys() {
        return primaryKeys;
    }
}

批量对象列表包装

package org.wit.ff.jdbc.id;

import java.util.List;

public class BatchInsertEntities<T extends IdGenerator> {
    private final List<T> entities;

    public BatchInsertEntities(List<T> entities) {
        this.entities = entities;
    }

    /**
     * <p>
     * The entities will be batch inserted into DB. The entities are also the
     * parameters of the
     * {@link org.apache.ibatis.binding.MapperMethod.SqlCommand}.
     */
    public List<T> getEntities() {
        return entities;
    }
}

自定义TypeHandler

package org.wit.ff.jdbc.id;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.LinkedList;
import java.util.List;

import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;

public class BatchInsertEntitiesTypeHandler extends BaseTypeHandler<BatchInsertEntityPrimaryKeys> {

    public BatchInsertEntityPrimaryKeys getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        // Read the primary key values from result set. It is believed that
        // there is 1 primary key column.
        List<String> pks = new LinkedList<>();
        do {
            // rs.next is called before.
            pks.add(rs.getString(columnIndex));
        } while (rs.next());

        return new BatchInsertEntityPrimaryKeys(pks);
    }

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, BatchInsertEntityPrimaryKeys parameter,
            JdbcType jdbcType) throws SQLException {
        // TODO Auto-generated method stub
        //System.out.println(" BatchInsertEntitiesTypeHandler#setNonNullParameter got called. ");
    }

    @Override
    public BatchInsertEntityPrimaryKeys getNullableResult(ResultSet rs, String columnName) throws SQLException {
        // TODO Auto-generated method stub
        //System.out.println(" BatchInsertEntitiesTypeHandler#getNullableResult got called. ");
        return null;
    }

    @Override
    public BatchInsertEntityPrimaryKeys getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        // TODO Auto-generated method stub
        //System.out.println(" BatchInsertEntitiesTypeHandler#getNullableResult got called. ");
        return null;
    }

}

自定义ObjectWrapper

package org.wit.ff.jdbc.id;

import java.util.Iterator;
import java.util.List;

import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.reflection.factory.ObjectFactory;
import org.apache.ibatis.reflection.property.PropertyTokenizer;
import org.apache.ibatis.reflection.wrapper.ObjectWrapper;

/**
 * Wrap the collection object for batch insert.
 * https://github.com/jactive/java
 */
public class BatchInsertObjectWrapper implements ObjectWrapper {

    private final BatchInsertEntities<IdGenerator> entity;

    public BatchInsertObjectWrapper(MetaObject metaObject, BatchInsertEntities<IdGenerator> object) {
        this.entity = object;
    }

    @Override
    public void set(PropertyTokenizer prop, Object value) {
        // check the primary key type existed or not when setting PK by reflection.
        BatchInsertEntityPrimaryKeys pks = (BatchInsertEntityPrimaryKeys) value;
        if (pks.getPrimaryKeys().size() == entity.getEntities().size()) {

            Iterator<String> iterPks = pks.getPrimaryKeys().iterator();
            Iterator<IdGenerator> iterEntities = entity.getEntities().iterator();

            while (iterPks.hasNext()) {
                String id = iterPks.next();
                IdGenerator entity = iterEntities.next();
                //System.out.println(id + "|" + entity);
                entity.parseGenKey(new Object[]{id});
            }
        }
    }

    @Override
    public Object get(PropertyTokenizer prop) {
        // Only the entities or parameters property of BatchInsertEntities
        // can be accessed by mapper.
        // 这一段是决定最终返回数据结果.
        if ("entities".equals(prop.getName()) ||
                "parameters".equals(prop.getName())) {
            return entity.getEntities();
        }

        return null;
    }

    @Override
    public String findProperty(String name, boolean useCamelCaseMapping) {
        return null;
    }

    @Override
    public String[] getGetterNames() {
        return null;
    }

    @Override
    public String[] getSetterNames() {
        return null;
    }


    /**
     * 此函数返回类型和BatchInsertEntitiesTypeHandler的泛型类型一致.
     * Jdbc3KeyGenerator.
     * Class<?> keyPropertyType = metaParam.getSetterType(keyProperties[i]);
     * TypeHandler<?> th = typeHandlerRegistry.getTypeHandler(keyPropertyType);
     *
     * @param name
     * @return
     * @see org.apache.ibatis.reflection.wrapper.ObjectWrapper#getSetterType(java.lang.String)
     */
    @Override
    public Class<?> getSetterType(String name) {
        // Return the primary key setter type.
        // Here, we return the BatchInsertEntityPrimaryKeys because
        // there are several primary keys  in the result set of
        // INSERT statement.
        return BatchInsertEntityPrimaryKeys.class;
    }

    @Override
    public Class<?> getGetterType(String name) {
        return null;
    }

    @Override
    public boolean hasSetter(String name) {
        // In BatchInsertObjectWrapper, name is the primary key property name.
        // Always return true here without checking if there is such property
        // in BatchInsertEntities#getEntities().get(0) . The verification be
        // postphone until setting the PK value at this.set method.
        return true;
    }

    @Override
    public boolean hasGetter(String name) {
        return false;
    }

    @Override
    public MetaObject instantiatePropertyValue(String name, PropertyTokenizer prop, ObjectFactory objectFactory) {
        return null;
    }

    @Override
    public boolean isCollection() {
        return false;
    }

    @Override
    public void add(Object element) {

    }

    @Override
    public <E> void addAll(List<E> element) {
    }
}

自定义ObjectWrapperFactory

package org.wit.ff.jdbc.id;

import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.reflection.wrapper.ObjectWrapper;
import org.apache.ibatis.reflection.wrapper.ObjectWrapperFactory;

public class BatchInsertObjectWrapperFactory implements ObjectWrapperFactory {
    public boolean hasWrapperFor(Object object) {
        return null != object && BatchInsertEntities.class.isAssignableFrom(object.getClass());
    }

    public ObjectWrapper getWrapperFor(MetaObject metaObject, Object object) {
        return new BatchInsertObjectWrapper(metaObject, (BatchInsertEntities<IdGenerator>)object);
    }

}

源代码分析#

• 为什么定义一个BatchInsertEntities而不直接使用List
• 自定义TypeHandler的目的
• 自定义ObjectWrapper(factory)

此事要回到源码当中找答案。

1）上文的时序图定位主键核心处理代码起始方法：org.apache.ibatis.executor.keygen.Jdbc3KeyGenerator.populateAfter

**注意mapper配置文件配置 useGeneratedKeys="true" keyProperty="id" keyColumn="ID" **

   public void processAfter(Executor executor, MappedStatement ms, Statement stmt, Object parameter) {
    List<Object> parameters = new ArrayList<Object>();
    parameters.add(parameter);
    processBatch(ms, stmt, parameters);
  }
  
  public void processBatch(MappedStatement ms, Statement stmt, List<Object> parameters) {
    ResultSet rs = null;
    try {
      rs = stmt.getGeneratedKeys();
      final Configuration configuration = ms.getConfiguration();
      final TypeHandlerRegistry typeHandlerRegistry = configuration.getTypeHandlerRegistry();
      final String[] keyProperties = ms.getKeyProperties();
      final ResultSetMetaData rsmd = rs.getMetaData();
      TypeHandler<?>[] typeHandlers = null;
      if (keyProperties != null && rsmd.getColumnCount() >= keyProperties.length) {
        for (Object parameter : parameters) {
          if (!rs.next()) break; // there should be one row for each statement (also one for each parameter)
          final MetaObject metaParam = configuration.newMetaObject(parameter);
          // 1,找typeHandlers的逻辑为关键.
          if (typeHandlers == null) typeHandlers = getTypeHandlers(typeHandlerRegistry, metaParam, keyProperties);
          // 2, 填充键值.
          populateKeys(rs, metaParam, keyProperties, typeHandlers);
        }
      }
    } catch (Exception e) {
      throw new ExecutorException("Error getting generated key or setting result to parameter object. Cause: " + e, e);
    } finally {
      if (rs != null) {
        try {
          rs.close();
        } catch (Exception e) {
          // ignore
        }
      }
    }
  }

步骤1 查找TypeHandler

BatchInsertEntitiesTypeHandler负责处理BatchInsertEntityPrimaryKeys类型，并定义了getNull(rs,int index)方法，后面可以看到这个方法在主键填充时被调用.

private TypeHandler<?>[] getTypeHandlers(TypeHandlerRegistry typeHandlerRegistry, MetaObject metaParam, String[] keyProperties) {
    TypeHandler<?>[] typeHandlers = new TypeHandler<?>[keyProperties.length];
    for (int i = 0; i < keyProperties.length; i++) {
      if (metaParam.hasSetter(keyProperties[i])) {
        // metaParam getSetterType --> BatchInsertObjectWrapper定义了getSetterType，参考MetaObject中获取getSetterType的源码，实际是从自定义的ObjectWrapper中获取
        Class<?> keyPropertyType = metaParam.getSetterType(keyProperties[i]);
        // 从spring xml 配置中找TypeHandler的配置.
        TypeHandler<?> th = typeHandlerRegistry.getTypeHandler(keyPropertyType);
        typeHandlers[i] = th;
      }
    }
    return typeHandlers;
  }

小结：获取TypeHandler的过程实际是依据ObjectWrapper指定的SetterType拿到KeyPropertyType(主键类型)，再通过主键类型从用户配置的SessionFactory当中获取(上文SessionFactory中配置BatchInsertEntitiesTypeHandler)

步骤2 填充主键

请参考BaseTypehandler中的getResult方法，实际调用了getNullResult方法，此方法BatchInsertEntitiesTypeHandler已有实现，经过调试发现它依据配置的主键名称"id"从resultset中获取了一列id值。

  private void populateKeys(ResultSet rs, MetaObject metaParam, String[] keyProperties, TypeHandler<?>[] typeHandlers) throws SQLException {
    for (int i = 0; i < keyProperties.length; i++) {
      TypeHandler<?> th = typeHandlers[i];
      if (th != null) {
       // 即调用BatchInsertEntitiesTypeHandler的public BatchInsertEntityPrimaryKeys getNullableResult(ResultSet rs, int columnIndex)的方法
       // 将主键值记录在BatchInsertEntityPrimaryKeys的对象当中，此时value的类型是BatchInsertEntityPrimaryKeys.
        Object value = th.getResult(rs, i + 1);
        // 调用  org.apache.ibatis.reflection.MetaObject
        metaParam.setValue(keyProperties[i], value);
      }
    }
  }
  
  public void setValue(String name, Object value) {
    // 被设置的属性是不含有"." , 目前是id, 而不是(item.id)这样的字符串 因此会执行else.
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      MetaObject metaValue = metaObjectForProperty(prop.getIndexedName());
      if (metaValue == SystemMetaObject.NULL_META_OBJECT) {
        if (value == null && prop.getChildren() != null) {
          return; // don't instantiate child path if value is null
        } else {
          metaValue = objectWrapper.instantiatePropertyValue(name, prop, objectFactory);
        }
      }
      metaValue.setValue(prop.getChildren(), value);
    } else {
      // 核心执行逻辑.
      // 此处的objectWrapper 对应我们自定义的org.wit.ff.BatchInsertObjectWrapper
      objectWrapper.set(prop, value);
    }
  }

小结：依据目标TypeHandler，调用getNullResult处理主键，从ResultSet当中拿到一列主键值，并包装成BatchInsertEntityPrimaryKeys返回，作为参数执行目标ObjectWrapper的set方法，请参考上文BatchInsertObjectWrapper。

至此，从ResultSet返回的主键值列表已经被我们自定义的ObjectWrapper截获。

步骤3 BatchInsertObjectWrapper填充主键值到原始对象列表
HowTown类型实现了IdGenerator接口, 调用parseGenKey即可填充主键到目标对象上，详情参考上文的HownTown源码。

    @Override
    public void set(PropertyTokenizer prop, Object value) {
        // check the primary key type existed or not when setting PK by reflection.
        BatchInsertEntityPrimaryKeys pks = (BatchInsertEntityPrimaryKeys) value;
        if (pks.getPrimaryKeys().size() == entity.getEntities().size()) {

            Iterator<String> iterPks = pks.getPrimaryKeys().iterator();
            Iterator<IdGenerator> iterEntities = entity.getEntities().iterator();

            while (iterPks.hasNext()) {
                String id = iterPks.next();
                IdGenerator entity = iterEntities.next();
                //System.out.println(id + "|" + entity);
                entity.parseGenKey(new Object[]{id});
            }
        }
    }

三个问题的答案##

1）自定义存储对象列表的结构的原因在于MyBatis处理主键时始终将对象作为"一个"来看待，并且要绑定主键类型，而List是集合类型，类型是List
2）由于1）中自定义了存储结构(BatchInsertEntities)需要处理主键，因此需要定义一个新的主键类型BatchInsertEntityPrimaryKeys 并绑定一个TypeHandler才可以处理此类型
3) ObjectWrapper和TypeHandler实际上是相辅相成的关系，有了类型处理器将ResultSet中的主键数据转换为目标对象可接受的类型，那么填充目标对象主键的工作就由ObjectWrapper来完成了，它们是相互协作的关系。

总结#

如果仍然对上述过程有疑问，请务必调试代码，作者不太聪明，调试了n次才读懂了完整过程。
最后给个提示，一个普通Bean是如何填充主键的，请查看org.apache.ibatis.reflection.wrapper.BeanWrapper及org.apache.ibatis.executor.keygen.Jdbc3KeyGenerator，想必必有收获。

QA#

太累了，这一篇。。。