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Java的MyBatis框架中实现多表连接查询和查询结果分页

程序员文章站 2024-03-09 12:35:41
实现多表联合查询 还是在david.mybatis.model包下面新建一个website类,用来持久化数据之用,重写下相应tostring()方法,方便测试程序之用。...

实现多表联合查询

还是在david.mybatis.model包下面新建一个website类,用来持久化数据之用,重写下相应tostring()方法,方便测试程序之用。

package david.mybatis.model;

import java.text.simpledateformat;
import java.util.date;

public class website {
  private int id;
  private string name;
  private int visitorid;
  private int status;
  private date createtime;
  private visitor visitor;

  public website() {
    // todo auto-generated constructor stub
    createtime = new date();
    visitor = new visitor();
  }

  public website(string name, int visitorid) {
    this.name = name;
    this.visitorid = visitorid;
    visitor = new visitor();
    status = 1;
    createtime = new date();
  }

  public int getid() {
    return id;
  }

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

  public visitor getvisitor() {
    return visitor;
  }

  public void setvisitor(visitor visitor) {
    this.visitor = visitor;
  }

  public string getname() {
    return name;
  }

  public void setname(string name) {
    this.name = name;
  }

  public int getstatus() {
    return status;
  }

  public void setstatus(int status) {
    this.status = status;
  }

  public date getcreatetime() {
    return createtime;
  }

  public void setcreatetime(date createtime) {
    this.createtime = createtime;
  }

  public int getvisitorid() {
    int id = 0;
    if (visitor == null)
      id = visitorid;
    else
      id = visitor.getid();
    return id;
  }

  public void setvisitorid(int visitorid) {
    this.visitorid = visitorid;
  }

  @override
  public string tostring() {
    stringbuilder sb = new stringbuilder(string.format("website=> {id:%d, name:%s, createtime:%s}\r\n", id, name,
        new simpledateformat("yyyy-mm-dd hh:mm:ss").format(createtime)));
    if (visitor != null)
      sb.append(string.format("visitor=> %s", visitor.tostring()));
    return sb.tostring();
  }
}

在david.mybatis.demo下面分别新建相应的操作接口:

package david.mybatis.demo;

import java.util.list;
import david.mybatis.model.website;

public interface iwebsiteoperation {
  
  public int add(website website);
  
  public int delete(int id);
  
  public int update(website website);
  
  public website query(int id);
  
  public list<website> getlist();
  
}

在mapper文件夹下新建websitemapper.xml映射文件,分别参照上一张所说的把增删改查的单表操作配置分别放进去,这样你可以建造一点测试数据。如下

<?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="david.mybatis.demo.iwebsiteoperation">
  <sql id="getlistsql">
    select id,
    name, visitorid, status, createtime from website
    where status>0
  </sql>
  <insert id="add" parametertype="website" usegeneratedkeys="true"
    keyproperty="id">
    insert into website (name, visitorid, status, createtime)
    values (#{name}, #{visitorid}, #{status}, #{createtime})
  </insert>
  <delete id="delete" parametertype="int">
    delete from website where
    status>0 and id = #{id}
  </delete>
  <update id="update" parametertype="website">
    update website set
    name=#{name} where status>0 and id=#{id}
  </update>
  <select id="query" parametertype="int" resultmap="websiters">
    select
    website.id siteid, website.name sitename, visitor.id visitorid,
    visitor.name visitorname,
    website.status sitestatus, website.createtime
    sitecreatetime from website
    inner join visitor on website.visitorid =
    visitor.id where website.status>0 and
    website.id=#{id}
  </select>
  <resultmap type="website" id="websiters">
    <id column="siteid" property="id" />
    <result column="sitename" property="name" />
    <result column="sitestatus" property="status" />
    <result column="sitecreatetime" property="createtime" />
    <association property="visitor" javatype="visitor" resultmap="visitorrs" />
  </resultmap>
  <resultmap type="visitor" id="visitorrs">
    <id column="visitorid" property="id" />
    <result column="visitorname" property="name" />
  </resultmap>
  <select id="getlist" resultmap="websitebyvisitoridrs">
  <include refid="getlistsql" />
  </select>  
</mapper>

这里今天主要说的就是那个查,现在我们想要查询网站的同时分别把相应的访问者信息一起拿出来,怎么做呢,大家可以参照配置中的query,写下联表查询的sql,

这里主要要注意的是,website实体与visit的实体里面id与name这2个属性都是一样的,所以为了避免映射出现出错现象,把相应的查询结果列起上不一样的别名,这样绑定的时候就可以避免。

假如我像下面一样配置会得到什么呢?

<select id="query" parametertype="int" resultmap="websiters">
  select
  website.id, website.name sitename, visitor.id,
  visitor.name visitorname,
  website.status sitestatus, website.createtime
  sitecreatetime from website
  inner join visitor on website.visitorid =
  visitor.id where website.status>0 and
  website.id=#{id}
</select>
<resultmap type="website" id="websiters">
  <id column="id" property="id" />
  <result column="sitename" property="name" />
  <result column="sitestatus" property="status" />
  <result column="sitecreatetime" property="createtime" />
  <association property="visitor" javatype="visitor"
    resultmap="visitorrs" />
</resultmap>
<resultmap type="visitor" id="visitorrs">
  <id column="id" property="id" />
  <result column="visitorname" property="name" />
</resultmap>

Java的MyBatis框架中实现多表连接查询和查询结果分页

有木有发觉,visitor的id也变成2了,这个其实它默认映射了website的id,因为sql语句查询出来的结果2个id都是变成2了,有人会问为什么不是4呢,因为他默认匹配第一个如果你把website.id与visit.id的位置,相互换下就会发现结果又神奇的变了

Java的MyBatis框架中实现多表连接查询和查询结果分页

所以需要起个别名避免这种情况,这样你就会发现真相其实只有一个就是下面的:

Java的MyBatis框架中实现多表连接查询和查询结果分页

大家可以看到其实多表处理resultmap的方式和单表是一致的,也无非是吧列明与javabean属性名成对应上去,可以看到在website的<resultmap>节点里面前台另外一个resultmap,他就是代表visit实体所需要映射的实体,可以使用以下方式进行关联

<association property="visitor" javatype="visitor" resultmap="visitorrs" />

其中的visitor就是website实体中的visit字段名,必须保证名称一致,否则就会抛出there is no getter for property named 'xxx' in 'class david.mybatis.model.website'的异常,这在上几章已经讲述了,当然如果你觉得不用嵌套resultmap也行,嵌套也是出于其他地方可以还要用到这个配置那就提炼出来的过程,也是抽象出来的一种思想。具体使用<resultmap>中的id与result可以从官网查找相应区别说明:http://mybatis.github.io/mybatis-3/sqlmap-xml.html#result_maps

这样,一个简单的多表联合查询就出来啦~,如果还有更加复杂的查询业务费是在这个基础上些许的变通修改。

分页效果逻辑
下面要讲的是关于一个业务问题中我们常碰到的分页问题。在开发web项目的时候我们经常会使用到列表显示,一般我们都会用一些常用的列表控件例如,datatables(个人感觉十分不错),easy ui下面的那些封装好的表格控件。

  思路:在这些控件里要达到分页的效果,一般都会传2个参数,第一个是表示当前页的索引(一般从0开始),第二个表示当前页展示多少条业务记录,然后将相应的参数传递给list<t> getlist(pagenateargs args)方法,最终实现数据库中的分页时候我们可以使用limit关键词(针对mysql)进行分页,如果是oracle或者sql server他们都有自带的rownum函数可以使用。

  针对上述思路,首先我们需要还是一如既往的在demo.mybatis.model下面新建一个名为pagenateargs的分页参数实体类与一个名为sortdirectionenum的枚举类,里面包含当前页面索引pageindex, 当前页展示业务记录数pagesize, pagestart属性表示从第几条开始,(pagestart=pageindex*pagesize)因为limit关键词用法是表示【limit 起始条数(不包含),取几条】,orderfieldstr排序字段,orderdirectionstr 排序方向,所以具体创建如下:
package david.mybatis.model;

/*
 * 分页参数实体类
 */
public class pagenateargs {
  private int pageindex;
  private int pagesize;
  private int pagestart;
  private string orderfieldstr;
  private string orderdirectionstr;

  public pagenateargs() {
    // todo auto-generated constructor stub
  }

  public pagenateargs(int pageindex, int pagesize, string orderfieldstr, string orderdirectionstr) {
    this.pageindex = pageindex;
    this.pagesize = pagesize;
    this.orderfieldstr = orderfieldstr;
    this.orderdirectionstr = orderdirectionstr;
    pagestart = pageindex * pagesize;
  }

  public int getpageindex() {
    return pageindex;
  }

  public int getpagestart() {
    return pagestart;
  }

  public int getpagesize() {
    return pagesize;
  }

  public string orderfieldstr() {
    return orderfieldstr;
  }

  public string getorderdirectionstr() {
    return orderdirectionstr;
  }
}

package david.mybatis.model;

/*
 * 排序枚举
 */
public enum sortdirectionenum {
  /*
   * 升序
   */
  asc,
  
  /*
   * 降序
   */
  desc
}

  完成上面的步骤以后我们在ivisitoroperation接口类中继续添加一个方法public list<visitor> getlistbypagenate(pagenateargs args),前几章中我们其实已经有getlist方法了,这次的分页其实也就是在这个的基础上稍加改动即可,ivisitoroperation接口类改动后如下所示:

package david.mybatis.demo;

import java.util.list;
import david.mybatis.model.pagenateargs;
import david.mybatis.model.visitor;
import david.mybatis.model.visitorwithrn;

public interface ivisitoroperation {
  /*
   * 基础查询
   */
  public visitor basicquery(int id);

  /*
   * 添加访问者
   */
  public int add(visitor visitor);
  
  /*
   * 删除访问者
   */
  public int delete(int id);
  
  /*
   * 更新访问者
   */
  public int update(visitor visitor);
  
  /*
   * 查询访问者
   */
  public visitor query(int id);
  
  /*
   * 查询list
   */
  public list<visitor> getlist();
  
  /*
   * 分页查询list
   */
  public list<visitor> getlistbypagenate(pagenateargs args);  
}

  接下来我们就要开始动手改动我们的visitormapper.xml配置文件了,新增一个<select>节点id与参数类型参照前几章的方式配置好,如下此处新增的id就为getlistbypagenate,配置好以后如下

<?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="david.mybatis.demo.ivisitoroperation">
  <!-- usegeneratedkeys="true"代表是否使用自增长序列, keyproperty="id"指定自增长列是哪一列, parametertype="visitor"指定ivisitoroperation接口类中定义中所传的相应类型 -->
  <insert id="add" parametertype="visitor" usegeneratedkeys="true"
    keyproperty="id">
    insert into visitor (name, email, status, createtime)
    values (#{name}, #{email}, #{status}, #{createtime})
  </insert>
  <delete id="delete" parametertype="int">
    delete from visitor where
    status>0 and id = #{id}
  </delete>
  <update id="update" parametertype="visitor">
    update visitor set name =
    #{name}, email=#{email}, status=#{status} where id=#{id} and status>0;
  </update>
  <select id="query" parametertype="int" resulttype="visitor">
    select id,
    name, email, status, createtime from visitor where id=#{id} and
    status>0 order by id
  </select>
  <select id="basicquery" parametertype="int" resulttype="visitor">
    select *
    from visitor where id=#{id} and
    status>0 order by id
  </select>
  <select id="getlist" resultmap="visitorrs">
    <include refid="getlistsql" />
  </select>
  <sql id="getlistsql">
    select * from visitor where
    status>0
  </sql>
  <!-- 以下为新增部分用来分页,orderbysql这个提取出来是为了后面有示例复用 -->
  <resultmap type="visitor" id="visitorrs">
    <id column="id" property="id" />
    <result column="name" property="name" />
    <result column="email" property="email" />
    <result column="status" property="status" />
    <result column="createtime" property="createtime" />
  </resultmap>
  <select id="getlistbypagenate" parametertype="pagenateargs"
    resulttype="visitor">
    select * from (
    <include refid="getlistsql" /> <include refid="orderbysql"/>
    ) t <!-- #{}表示参数化输出,${}表示直接输出不进行任何转义操作,自己进行转移 -->
    <if test="pagestart>-1 and pagesize>-1">
      limit #{pagestart}, #{pagesize}
    </if>
  </select>
  <sql id="orderbysql">
    order by ${orderfieldstr} ${orderdirectionstr}
  </sql>
</mapper>

  在上面你会发现有类似,下图中的配置,这里面的字段属性都是针对pagenateargs参数类中的属性名,保持一致。

<if test="pagestart>-1 and pagesize>-1">
  limit #{pagestart}, #{pagesize}
</if>

   在demorun类中创建测试方法:

/*
 * 分页参数
 */
public static void queryvisitorlistwithpagenate(int pageindex, int pagesize, string orderfield, string orderdire) {
  pagenateargs args = new pagenateargs(pageindex, pagesize, orderfield, orderdire);
  sqlsession session = mybatisutils.getsqlsession();
  ivisitoroperation voperation = session.getmapper(ivisitoroperation.class);
  list<visitor> visitors = voperation.getlistbypagenate(args);
  for (visitor visitor : visitors) {
    system.out.println(visitor);
  }
  mybatisutils.closesession(session);
  mybatisutils.showmessages(crud_enum.list, visitors.size());
}

demorun.queryvisitorlistwithpagenate(0, 100, "id", sortdirectionenum.desc.tostring());

运行后下测试结果,先按id倒序排列,查的visitor表一共有14条记录,

Java的MyBatis框架中实现多表连接查询和查询结果分页

假设我们取在第2页取5条,执行下面也就是6-10条数据,这样传参数就行了

demorun.queryvisitorlistwithpagenate(1, 5, "id", sortdirectionenum.desc.tostring());

结果如下:

Java的MyBatis框架中实现多表连接查询和查询结果分页

这样就自己实现了的一个分页逻辑啦~^0^,这里需要注意的就是我这边orderfieldstr字段是没有做过任何判断的,理论上要处理下防止错误了列名传进去,不过现在网上应该有现成封装好的东西,大家也可以去google下,这里只是给个思路演示下怎么用mybatis分页。

  完成这个后,因为是mysql的关系所以在查询结果里他没有自带rownum序列id,所以查看测试数据是第几条的时候可能不明显,不zao急,我们可以自己动手丰衣足食改造下上面的方法,这里我重新在model包里新建一个一模一样的visitorwithrn实体里面多带一个rownum参数持久化返回的rownumid,如下:

package david.mybatis.model;

import java.text.simpledateformat;
import java.util.date;

public class visitorwithrn {
  private int id;
  private string name;
  private string email;
  private int status;
  private date createtime;
  private int rownum;

  public visitorwithrn() {
    // todo auto-generated constructor stub
    createtime = new date();
  }

  public visitorwithrn(string name, string email) {
    this.name = name;
    this.email = email;
    this.setstatus(1);
    this.createtime = new date();
  }

  public int getid() {
    return id;
  }

  public void setname(string name) {
    this.name = name;
  }

  public string getname() {
    return name;
  }

  public void setemail(string email) {
    this.email = email;
  }

  public string getemail() {
    return email;
  }

  public date getcreatetime() {
    return createtime;
  }

  public int getstatus() {
    return status;
  }

  public void setstatus(int status) {
    this.status = status;
  }

  public int getrownum() {
    return rownum;
  }

  public void setrownum(int rownum) {
    this.rownum = rownum;
  }

  @override
  public string tostring() {
    // todo auto-generated method stub
    return string.format("{rownum:%d, id: %d, name: %s, createtime: %s}", rownum, id, name,
        new simpledateformat("yyyy-mm-dd hh:mm:ss").format(createtime));
  }
}

在ivisitoroperation里面在新建一个名为 public list<visitorwithrn> getlistbypagenatewithrn(pagenateargs args)的方法,同样我们需要在visitormapper中配置下相应<select>节点与脚本,此处唯一的不同就是需要改下sql脚本,如下:

<?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="david.mybatis.demo.ivisitoroperation">
  <!-- usegeneratedkeys="true"代表是否使用自增长序列, keyproperty="id"指定自增长列是哪一列, parametertype="visitor"指定ivisitoroperation接口类中定义中所传的相应类型 -->
  <insert id="add" parametertype="visitor" usegeneratedkeys="true"
    keyproperty="id">
    insert into visitor (name, email, status, createtime)
    values (#{name}, #{email}, #{status}, #{createtime})
  </insert>
  <delete id="delete" parametertype="int">
    delete from visitor where
    status>0 and id = #{id}
  </delete>
  <update id="update" parametertype="visitor">
    update visitor set name =
    #{name}, email=#{email}, status=#{status} where id=#{id} and status>0;
  </update>
  <select id="query" parametertype="int" resulttype="visitor">
    select id,
    name, email, status, createtime from visitor where id=#{id} and
    status>0 order by id
  </select>
  <select id="basicquery" parametertype="int" resulttype="visitor">
    select *
    from visitor where id=#{id} and
    status>0 order by id
  </select>
  <select id="getlist" resultmap="visitorrs">
    <include refid="getlistsql" />
  </select>
  <sql id="getlistsql">
    select * from visitor where
    status>0
  </sql>
  <resultmap type="visitor" id="visitorrs">
    <id column="id" property="id" />
    <result column="name" property="name" />
    <result column="email" property="email" />
    <result column="status" property="status" />
    <result column="createtime" property="createtime" />
  </resultmap>
  <select id="getlistbypagenate" parametertype="pagenateargs"
    resulttype="visitor">
    select * from (
    <include refid="getlistsql" /> <include refid="orderbysql"/>
    ) t <!-- #{}表示参数化输出,${}表示直接输出不进行任何转义操作,自己进行转移 -->
    <if test="pagestart>-1 and pagesize>-1">
      limit #{pagestart}, #{pagesize}
    </if>
  </select>
  <!--提炼出来为了2个示例共用下 -->
  <sql id="orderbysql">
    order by ${orderfieldstr} ${orderdirectionstr}
  </sql>
  <!-- 带rownum的sql脚本书写方式 -->
  <resultmap type="visitorwithrn" id="visitorwithrnrs">
    <id column="id" property="id" />
    <result column="name" property="name" />
    <result column="email" property="email" />
    <result column="status" property="status" />
    <result column="createtime" property="createtime" />
    <result column="rownum" property="rownum" />
  </resultmap>
  <select id="getlistbypagenatewithrn" resultmap="visitorwithrnrs">
    <!-- #{}表示参数化输出,${}表示直接输出不进行任何转义操作,自己进行转移 -->
    select t.rownum, t.id, t.name, t.email, t.status, t.createtime from (<include refid="getlistsqlcontainsrn" /> <include refid="orderbysql"/>) t
    <if test="pagestart>-1 and pagesize>-1">
      limit #{pagestart}, #{pagesize}
    </if>
  </select>
  <sql id="getlistsqlcontainsrn">
    select @rownum:=@rownum+1 rownum,
    result.id, result.name, result.email, result.status, result.createtime
    from (
    select @rownum:=0, visitor.* from visitor where
    status>0) result
  </sql>
</mapper>

接下来剩下的就是如刚才在demorun下面添加测试方法,这里就不贴图了,完成后你可以看到刚刚的6-10条数据会变成如下

Java的MyBatis框架中实现多表连接查询和查询结果分页