mybatis的一些知识点

一、collection 标签：用于定义关联的list集合类型的封装规则

例子：

public class CategoryVO {

    private Integer id;
    private String name;
    private String type;
    private Integer fatherId;

    // 三级分类vo list
    private List<SubCategoryVO> subCategoryVOList;

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public Integer getFatherId() {
        return fatherId;
    }

    public void setFatherId(Integer fatherId) {
        this.fatherId = fatherId;
    }

    public List<SubCategoryVO> getSubCategoryVOList() {
        return subCategoryVOList;
    }

    public void setSubCategoryVOList(List<SubCategoryVO> subCategoryVOList) {
        this.subCategoryVOList = subCategoryVOList;
    }
}

public class SubCategoryVO {

    private Integer subId;
    private String subName;
    private String subType;
    private Integer subFatherId;

    public Integer getSubId() {
        return subId;
    }

    public void setSubId(Integer subId) {
        this.subId = subId;
    }

    public String getSubName() {
        return subName;
    }

    public void setSubName(String subName) {
        this.subName = subName;
    }

    public String getSubType() {
        return subType;
    }

    public void setSubType(String subType) {
        this.subType = subType;
    }

    public Integer getSubFatherId() {
        return subFatherId;
    }

    public void setSubFatherId(Integer subFatherId) {
        this.subFatherId = subFatherId;
    }
}

CategoryVO 里有list字段SubCategoryVO，查询的时候，要使用collection在xml里进行配置

 <resultMap id="myCategoryVO" type="com.zb.pojo.vo.CategoryVO">
    <id column="id" property="id"/>
    <result column="name" property="name"/>
    <result column="type" property="type"/>
    <result column="fatherId" property="fatherId"/>

    <!--
      collection 标签：用于定义关联的list集合类型的封装规则
      property：对应三级分类的list属性名
      ofType：集合的类型，三级分类的vo
    -->
    <collection property="subCategoryVOList" ofType="com.zb.pojo.vo.SubCategoryVO">
      <id column="subId" property="subId"/>
      <result column="subName" property="subName"/>
      <result column="subType" property="subType"/>
      <result column="subFatherId" property="subFatherId"/>
    </collection>
  </resultMap>

  <select id="getSubCatList" resultMap="myCategoryVO" parameterType="int">
     SELECT
        f.id as id,
        f.`name` as `name`,
        f.type as type,
        f.father_id as fatherId,
        c.id as subId,
        c.`name` as subName,
        c.type as subType,
        c.father_id as subFatherId
    FROM
        category f
    LEFT JOIN
        category c
    on
        f.id = c.father_id
    WHERE
        f.father_id = #{rootCatId}
  </select>

这样就可以查询出包含列表的数据：

{
    "status": 200,
    "msg": "OK",
    "data": [
        {
            "id": 11,
            "name": "蛋糕",
            "type": "2",
            "fatherId": 1,
            "subCategoryVOList": [
                {
                    "subId": 37,
                    "subName": "蒸蛋糕",
                    "subType": "3",
                    "subFatherId": 11
                },
                {
                    "subId": 38,
                    "subName": "软面包",
                    "subType": "3",
                    "subFatherId": 11
                },
                {
                    "subId": 39,
                    "subName": "脱水蛋糕",
                    "subType": "3",
                    "subFatherId": 11
                },
                {
                    "subId": 40,
                    "subName": "马卡龙",
                    "subType": "3",
                    "subFatherId": 11
                },
                {
                    "subId": 41,
                    "subName": "甜甜圈",
                    "subType": "3",
                    "subFatherId": 11
                },
                {
                    "subId": 42,
                    "subName": "三明治",
                    "subType": "3",
                    "subFatherId": 11
                },
                {
                    "subId": 43,
                    "subName": "铜锣烧",
                    "subType": "3",
                    "subFatherId": 11
                }
            ]
        },
        {
            "id": 12,
            "name": "点心",
            "type": "2",
            "fatherId": 1,
            "subCategoryVOList": [
                {
                    "subId": 44,
                    "subName": "肉松饼",
                    "subType": "3",
                    "subFatherId": 12
                },
                {
                    "subId": 45,
                    "subName": "华夫饼",
                    "subType": "3",
                    "subFatherId": 12
                },
                {
                    "subId": 46,
                    "subName": "沙琪玛",
                    "subType": "3",
                    "subFatherId": 12
                },
                {
                    "subId": 47,
                    "subName": "鸡蛋卷",
                    "subType": "3",
                    "subFatherId": 12
                },
                {
                    "subId": 48,
                    "subName": "蛋饼",
                    "subType": "3",
                    "subFatherId": 12
                },
                {
                    "subId": 49,
                    "subName": "凤梨酥",
                    "subType": "3",
                    "subFatherId": 12
                },
                {
                    "subId": 50,
                    "subName": "手撕面包",
                    "subType": "3",
                    "subFatherId": 12
                }
            ]
        }
    ]
}