java表的分组查询collection用法

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最近在学习java做项目中遇到了关联查询之后要填充modl，但是model是分组的，里面有多个数组，如果只是用关联查询，对于这种会出现重复查询，所以这里要用到Mybatis的collection来处理

1、首先介绍一下我们的model属性（可以看到有2个指定对象的数组）

    private Long id;
    private String customerNo;
    private Long listId;
    private String name;
    private String identifyType;
    private String identifyNo;   
    private String phoneA;
    private String phoneB;
    private String phoneC;
    private String telephone;
    private String email;
    private String idcardAdress;
    private String householdAddress;
    private String liveAddress;
    private String workAddress;
    private Date gmtCreate;
    private Date gmtModified;
    private Long createBy;
    private Long lastUpdateBy;
    private String customerType;
    private List contactList;
    private List bankcardList;

2、在mapper里面对接输出model

3、在mapper的xml里写关联查询

  SELECT
customer . id,
customer .customer_no ,
customer .list_id ,
customer . name ,
customer .identify_type,
customer .identify_no ,
customer .phone_a ,
customer .phone_b ,
customer .phone_c ,
customer .telephone,
customer .email,
customer .idcard_adress,
customer .household_address,
customer .live_address,
customer .work_address,
customer .customer_type,
contact . id AS contact_id,
contact .relation_type,
contact .identify_type AS contact_identify_type,
contact .identify_no AS contact_identify_no,
contact .contact_name,
contact .contact_phone,
bankcard. id AS bankcard_id,
bankcard.card_bank,
bankcard.account_type,
bankcard.bank_card_no
FROM
cm_customer customer
LEFT JOIN cm_customer_contact contact ON customer.id = contact.customer_id
LEFT JOIN cm_customer_bankcard bankcard ON customer.id = bankcard.customer_id 
  

简单3步就完成了分组查询，其中要注意BaseResultMap1中表属性对应的要与自己创建的匿名表列名对应（区分相同字段在不同表中的情况）
详细的collection用法和Association用法可参考https://blog.csdn.net/qq_38157516/article/details/79712721