create table Category (
Id int not null auto_increment,
Name varchar(80) null,
constraint pk_category primary key (Id)
);
INSERT INTO category(Name) VALUES ('女装');
INSERT INTO category(Name) VALUES ('美妆');
INSERT INTO category(Name) VALUES ('书籍');
create table product (
Id int not null auto_increment,
categoryId int not null,
Name varchar(80) null,
constraint pk_product primary key (Id),
constraint fk_product_2 foreign key (categoryId)
references category (Id)
);
create index productCat on product (categoryId);
create index productName on product (Name);
INSERT INTO product(CategoryId,Name) VALUES (1, '裂帛');
INSERT INTO product(CategoryId,Name) VALUES (1, '雅鹿');
INSERT INTO product(CategoryId,Name) VALUES (2,'膜法世家');
INSERT INTO product(CategoryId,Name) VALUES (2,'御泥坊');
INSERT INTO product(CategoryId,Name) VALUES (2, '雅诗兰黛');
INSERT INTO product(CategoryId,Name) VALUES (2, '欧莱雅');
INSERT INTO product(CategoryId,Name) VALUES (2, '韩后');
INSERT INTO product(CategoryId,Name) VALUES (2, '相宜本草');
INSERT INTO product(CategoryId,Name) VALUES (3,'疯狂JAVA');
INSERT INTO product(CategoryId,Name) VALUES (3,'JAVA核心技术');

<table tableName="category" enableCountByExample="true" enableDeleteByExample="true" enableSelectByExample="true" enableUpdateByExample="true">
 <generatedKey column="Id" sqlStatement="mysql" identity="true"/>
</table>
<table tableName="product" enableCountByExample="true" enableSelectByExample="true" enableSelectByPrimaryKey="true" enableUpdateByPrimaryKey="true" enableDeleteByPrimaryKey="true" enableInsert="true">
 <generatedKey column="Id" sqlStatement="mysql" identity="true"></generatedKey>
</table>

public class CategoryDto {
 private Category category;
 private List<Product> products;
 private int id;
 public int getId() {
 return id;
 }
 public void setId(int id) {
 this.id = id;
 }
 public Category getCategory() {
 return category;
 }
 public void setCategory(Category category) {
 this.category = category;
 }
 public List<Product> getProducts() {
 return products;
 }
 public void setProducts(List<Product> products) {
 this.products = products;
 }
}

 <select id="getById" parameterType="java.lang.Integer" resultMap="CategoryResult">
 SELECT Category.Id AS CateId,Category.Name AS CateName,Product.Id AS ProductId,Product.Name AS ProductName
 FROM Category,Product
 WHERE Category.Id=Product.CategoryId AND Category.Id=#{id}
 </select>

<resultMap id="CategoryResult" type="com.data.dto.CategoryDto">
 <association property="category" javaType="com.data.pojo.Category">
 <result property="id" column="CateId"></result>
 <result property="name" column="CateName"></result>
 </association>
 <collection property="products" ofType="com.data.pojo.Product">
 <result property="id" column="ProductId"></result>
 <result property="name" column="ProductName"></result>
 </collection>
 </resultMap> 

@Test
 public void test_getById(){
 int id=2;
 CategoryDto dto= categoryMapper.getById(id);
 if(dto==null){
 System.out.println("不存在");
 }else {
 System.out.println("商品id="+dto.getId()+" name="+dto.getCategory().getName());
 System.out.println("Products："+dto.getProducts().size());
 for(Product product:dto.getProducts()){
 System.out.println(" |_"+product.getName());
 }
 }
 }

<resultMap id="CategoryResult" type="com.data.dto.CategoryDto">
 <id property="id" column="CateId"></id>
……
</resultMap>