jooq_DSL入门

org.jooq.impl.DSL是生成所有jooq对象的主要类。作为一个静态的工厂去生成数据库表表达式、列表达式、条件表达式和其它查询部分。使用dsl时，导入org.jooq.impl.DSL.*

DSLContext和DSL 是访问JOOQ类和功能的主要入口点。

如：

创建一个常量值的字段，

    Field field = DSL.val("hello world");

Condition condition = DSL.exists(DSL.select(DSL.field("username")));等价于select * from 表 where exists (select username from dual);

获取表记录对象：

    Table table = DSL.table("atfc_elecoco_pict");

根据数据库连接生成操作数据库的对象

    DSLContext dsl = DSL.using(connection);

DSLContext引用了org.jooq.Configuration。。。Configuration配置了jooq的行为

小例子：

DSLContext dslContext = DSL.using(connection);

Resultrecords = dslContext.select().from(table).where("statu = 0").and("id > 4340").orderBy(DSL.field("time").asc()).fetch();
        for (Object aResult : records) {
            Record record = (Record) aResult;
            System.out.println(record);
        }

案例：我想关联查询TB_ELECOCOC和TB_ELECOCO_DAPARTMENT，两个表通过appid关联，，我想查询TB_ELECOCOC中RESULTSTRING为""的，TB_ELECOCO_DAPARTMENT中的MODULEOWNER字段。。。还有要去重

对应的sql语句可以为：

    select DISTINCT d.moduleowner
    from tb_elecoco e
    left join tb_elecoco_dapartment d on e.appid = d.appid

    where e.resultstring = "";

    select d.appid,d.moduleowner
    from tb_elecoco e,tb_elecoco_dapartment d

    where e.appid = d.appid and e.resultstring = "";

我们用join。。。。

1、创建DO，虽然里面只有一个字段但是我还是创建了一个do用来匹配查询结果：

package me.ele.xxx.xxx.xxx;

public class QueryElecocoOwnerEmailDo {
    //private String appId;
    private String moduleOwner;

    public String getModuleOwner() {
        return moduleOwner;
    }

    public void setModuleOwner(String moduleOwner) {
        this.moduleOwner = moduleOwner;
    }

    @Override
    public String toString() {
        return "QueryElecocoOwnerEmailDo{" +
                "moduleOwner='" + moduleOwner + '\'' +
                '}';
    }

}

2、创建查询类，类中需要有数据库相关的信息，如，数据库url，username，password

package me.ele.xxx.xxx.xx;

import org.jooq.*;
import org.jooq.impl.DSL;

import java.sql.Connection;
import java.sql.DriverManager;
import java.util.List;

import static xxxx.xxx.xxx.TB_ELECOCO;//这块倒入的就是jooq根据数据库自动生成的那些class
import static xxx.xxx.xxx..TB_ELECOCO_DAPARTMENT;

public class QueryElecocoOwnerEmail {
    private static String driver="com.mysql.jdbc.Driver";
    private static String url="jdbc:mysql://127.0.0.1:3306/数据名";
    private static String username="用户名";
    private static String password="密码";

    private static Connection ct=null;
    private static DSLContext dslContext=null;

    static {
        try {
            Class.forName(driver);
            ct=DriverManager.getConnection(url, username, password);
            dslContext=DSL.using(ct);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    //查询方法getElecocoOwnerEmail(String 条件)。。
}

3、完善查询方法：

public List getElecocoOwnerEmail(String resultString) {

        List moduleOwners = dslContext.selectDistinct(TB_ELECOCO_DAPARTMENT.MODULEOWNER.as("moduleOwner"))
                .from(TB_ELECOCO_DAPARTMENT)
                .leftJoin(TB_ELECOCO)
                .on(TB_ELECOCO_DAPARTMENT.APPID.eq(TB_ELECOCO.APPID))
                .where(TB_ELECOCO.RESULTSTRING.eq(resultString))
                .fetchInto(QueryElecocoOwnerEmailDo.class);
        for(QueryElecocoOwnerEmailDo queryElecocoOwnerEmailDo : moduleOwners){
            String moduleOwner = queryElecocoOwnerEmailDo.getModuleOwner();
            if(moduleOwner.equals("xxx")){
                System.out.println("====");
            }
        }
        return moduleOwners;
    }

    public static void main(String[] args){
        QueryElecocoOwnerEmail q  = new QueryElecocoOwnerEmail();
        q.getElecocoOwnerEmail("");
    }