resultMap

多对一

多个Blog对应一个Type
Blog类

public class Blog {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String title;
    private String content;
    private String firstPicture;
    private String flag;
    private Integer views;
    private boolean appreciation;
    private boolean shareStatement;
    private boolean commenttabled;
    private boolean published;
    private boolean recommend;
    @Temporal(TemporalType.TIMESTAMP)
    private Date createTime;
    @Temporal(TemporalType.TIMESTAMP)
    private Date updateTime;
    @ManyToOne
    private Type type；

Type类

public class Type {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @NotEmpty(message="分类名称不能为空")
    private String name;

    @OneToMany(mappedBy = "type")
    private List<Blog> blogs = new ArrayList<>();

<!--定义Blog和Type的resultMap-->
	<!--column代表数据库字段，property代表实体类字段-->
    <resultMap id="blogtype" type="Blog">
        <id column="id" property="id"/>
        <result column="title" property="title"/>
        <result column="recommend" property="recommend"/>
        <result column="update_time" property="updateTime"/>
        <!--配置封装type的内容-->
        <!--此处的property代表Blog实体类中定义的Type，column代表数据库blog表中连接type表的外键type_id-->
        <association property="type" column="type_id" javaType="Type">
            <result column="name" property="name"/>
        </association>
    </resultMap>
    <!--查询语句如下-->
	<select id="findAll" resultMap="blogtype">
        select b.*,t.name from t_blog b,t_type t where b.type_id=t.id and 1=1
        <if test="title!=null">
            and title like '%' #{title} '%'
        </if>
        <if test="typeId!=null">
            and type_id = #{typeId}
        </if>
        <if test="recommend!=null">
            and recommend = #{recommend}
        </if>
    </select>