Mybatis多表查询记录

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前言

MySQL多表查询是项目中常用到的操作，今天在这里进行一次记录，方便以后使用`

当前的项目多使用springboot框架，其中与mysql的交互使用mybatis，mybatis多表查询比较重要，其实也很简单，这里进行记录。

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一、Mapper文件更改

1.不使用多表查询的mapper.xml写法

1.1 定义一个resultMap，其中是数据库表字段（column）和Java对象字段的映射（property），id为主键

	<resultMap type="ProcessFlow" id="ProcessFlowResult">
		<id     property="id"         column="id_"        />
		<result property="code"       column="code_"      />
		<result property="name"       column="name_"    />
		<result property="description"     column="description_"        />
		<result property="createBy"     column="create_by_"        />
		<result property="createTime"     column="create_time_"        />
		<result property="updateBy"     column="update_by_"        />
		<result property="updateTime"     column="update_time_"        />
		<result property="status"     column="status_"        />
		<result property="tenantId"     column="tenant_id_"        />
		<result property="jsonStr"     column="json_str_"        />
		<result property="graphLib"     column="graph_lib_"        />
		<result property="graphLibName"     column="graphLibName"        />
		<result property="canvasStyle"     column="canvas_style_"        />
		<result property="chart"     column="chart_"        />
	</resultMap>

1.2 定义一个sql，其中内容为要查询的字段，方便后续查询调用

<sql id="selectProcessFlowVo">
       select a.id_, a.code_, a.name_, a.description_, a.create_by_, a.create_time_, a.update_by_, a.update_time_,
		   a.status_, a.tenant_id_, a.json_str_, a.graph_lib_, a.canvas_style_, a.chart_, c.name_ as graphLibName from bv_process_flow a left join bv_comp_categ c on a.graph_lib_= c.id_
   </sql>

1.3 定义具体的批量/单个查询语句

<select id="list" parameterType="ProcessFlow" resultMap="ProcessFlowResult">
 	<include refid="selectProcessFlowVo"></include>
 	<where>
 		<if test="id != null and id != ''">and a.id_ = #{
    
    id}</if>
 		<if test="code != null and code != ''">and a.code_ like concat('%',  #{
    
    code}, '%')</if>
 		<if test="name != null and name != ''">and a.name_ like concat('%',  #{
    
    name}, '%')</if>
 		<if test="status != null and status != ''">and a.status_ = #{
    
    status}</if>
 		<if test="tenantId != null and tenantId != ''">and a.tenant_id_ = #{
    
    tenantId}</if>
 	</where>
 </select>

2.多表查询的mapper.xml写法

2.1 定义resultMap，和不使用多表查询的resultMap相比，添加了collection， 其property表示Java对象中，保存多表查询结果的list字段，如下面的charList，ofType为domain类型，即Chart

	<resultMap type="ProcessFlowWithCharts" id="ProcessFlowWithChartsResult">
		<id     property="id"         column="id_"        />
		<result property="code"       column="code_"      />
		<result property="name"       column="name_"    />
		<result property="description"     column="description_"        />
		<result property="createBy"     column="create_by_"        />
		<result property="createTime"     column="create_time_"        />
		<result property="updateBy"     column="update_by_"        />
		<result property="updateTime"     column="update_time_"        />
		<result property="status"     column="status_"        />
		<result property="tenantId"     column="tenant_id_"        />
		<result property="jsonStr"     column="json_str_"        />
		<result property="graphLib"     column="graph_lib_"        />
		<result property="graphLibName"     column="graphLibName"        />
		<result property="canvasStyle"     column="canvas_style_"        />
		<result property="chart"     column="chart_"        />
		<collection property="chartList" ofType="Chart">
			<id property="id" column="cId"/>
			<result property="code" column="cCode"/>
			<result property="name"       column="cName"    />
			<result property="description"     column="cDescription"        />
			<result property="createBy"     column="cCreateBy"        />
			<result property="createTime"     column="cCreateTime"        />
			<result property="left"     column="left_"        />
			<result property="top"     column="top_"        />
			<result property="height"     column="height_"        />
			<result property="width"     column="width_"        />
			<result property="zindex"     column="zindex_"        />
			<result property="dataSource"     column="dataSource_"        />
			<result property="processFlowId"     column="process_flow_id_"        />
		</collection>
	</resultMap>

2.2 多表查询sql

<select id="get" parameterType="String" resultMap="ProcessFlowWithChartsResult">
	select a.id_, a.code_, a.name_, a.description_, a.create_by_, a.create_time_, a.update_by_, a.update_time_,
		   a.status_, a.tenant_id_, a.json_str_, a.graph_lib_, a.canvas_style_, a.chart_, b.name_ as graphLibName,
		   c.id_ as cId, c.name_ as cName, c.code_ as cCode, c.description_ as cDescription, c.create_by_ as cCreateBy, c.create_time_ as cCreateTime,
		   c.left_, c.top_, c.height_, c.width_, c.zindex_, c.dataSource_, c.process_flow_id_
	from bv_process_flow a left join bv_comp_categ b on a.graph_lib_= b.id_ left join bv_chart c on a.id_=c.process_flow_id_ where a.id_=#{
    
    id}
</select>

2.3 多表查询Java对象，即domain定义

public class ProcessFlow {
    
    

    private String id;
    private String code;
    private String name;
    private String description;
    private String createBy;
    @JsonFormat(
            pattern = "yyyy-MM-dd HH:mm:ss"
    )
    private Date createTime;
    private String updateBy;
    @JsonFormat(
            pattern = "yyyy-MM-dd HH:mm:ss"
    )
    private Date updateTime;
    private String status;
    private String tenantId;
    private String jsonStr;
    private String graphLib;
    private String graphLibName;
    private String canvasStyle;
    private String chart;
	private List<Chart> chartList;
}

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总结

其实多表查询在mybatis中很好实现，主要是resultMap的设置添加collection，其后是Java对象添加List类型的对象列表即可。