Select 在 Northwind 数据库上使用 JPA 和 JDBC 模板

Question

我想像下面这样在 Northwind 数据库上执行 select 语句。

select distinct b.*, a.CategoryName
from Categories a
inner join Products b on a.CategoryID = b.CategoryID
where b.Discontinued = 'N'
order by b.ProductName;

关于这个操作我有两个问题：

我已经为 table 的类别和产品创建了 POJO，如下所示

Table 产品

@Entity
public class Products {
  @Id
  private Long productid;
  private String productname;
  private Long supplierid;
  @ManyToOne
  @JoinColumn(name = "categories", referencedColumnName = "categoryid")
  private Categories categoryid;
  private String quantityperunit;
  private Double unitprice;
  private Long unitsinstock;
  private Long unitsonorder;
  private Long reorderlevel;
  private String discontinued;

Table 类别

@Entity
public class Categories {
  @Id
  private Long categoryid;
  private String categoryname;
  private String description;
  private String picture;

现在我不知道如何为这个 table 编写 rowmapper（请在下面找到？？？？）

private static final RowMapper<Products> productsRowMapper = (rs, rowNum) ->{
        Products products = new Products();
        products.setProductid(rs.getLong("ProductID"));
        products.setProductname(rs.getString("ProductName"));
        products.setSupplierid(rs.getLong("SupplierID"));
        products.setCategoryid(rs.?????
        products.setQuantityperunit(rs.getString("QuantityPerUnit"));
        products.setUnitprice(rs.getDouble("UnitPrice"));
        products.setUnitsinstock(rs.getLong("UnitsInStock"));
        products.setUnitsonorder(rs.getLong("UnitsOnOrder"));
        products.setReorderlevel(rs.getLong("ReorderLevel"));
        products.setDiscontinued(rs.getString("Discontinued"));
        return products;
    };

第二个问题是不知道table商品中categoryid列的注解是否正确？

修正后

   @Repository
public class JdbcProductsDao implements ProductsDao{

    private final JdbcTemplate jdbcTemplate;

    @Autowired
    public JdbcProductsDao(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    private static final RowMapper<Products> productsRowMapper = (rs, rowNum) ->{
        Products products = new Products();
        products.setProductid(rs.getLong("ProductID"));
        products.setProductname(rs.getString("ProductName"));
        products.setSupplierid(rs.getLong("SupplierID"));
        products.setCategoryid(new Categories(rs.getString("CategoryName")));
        products.setQuantityperunit(rs.getString("QuantityPerUnit"));
        products.setUnitprice(rs.getDouble("UnitPrice"));
        products.setUnitsinstock(rs.getLong("UnitsInStock"));
        products.setUnitsonorder(rs.getLong("UnitsOnOrder"));
        products.setReorderlevel(rs.getLong("ReorderLevel"));
        products.setDiscontinued(rs.getString("Discontinued"));
        return products;
    };


    public Products findByProductName(String productname) {
        String sql = "SELECT * FROM products WHERE ProductName = ?";
        return jdbcTemplate.queryForObject(sql, productsRowMapper, productname);
    }

    public List<Products> sortByProductName(){
        String sql = "SELECT * FROM products order by ProductName asc";
        return jdbcTemplate.query(sql, productsRowMapper);
        }

Table 类别

@Entity
public class Categories {
  @Id
  private Long categoryid;
  @Column(name = "CategoryName")
  private String categoryname;
  private String description;
  private String picture;

  @OneToMany(mappedBy="categoryid")
  private List<Products> products;

Table 产品

   @Entity
public class Products {
  @Id
  private Long productid;
  @Column(name = "ProductName")
  private String productname;
  private Long supplierid;
  @ManyToOne
  private Categories categoryid;
  private String quantityperunit;
  private Double unitprice;
  private Long unitsinstock;
  private Long unitsonorder;
  private Long reorderlevel;
  private String discontinued;

Answer 1

Now I have no idea how to write rowmapper for this tables (please find below ????)

您必须像这样设置一个对象：

products.setCategoryid(new Categories(rs.getString("a.categoryname"));

_{我假设你有一个构造函数 Categories(String categoryname)}

注意：如果您想获得更多信息，您还必须更改查询和构造函数。

the second problem is that I don't know if the annotations on the column categoryid in the table products are correct?

我觉得没必要用@JoinColumn(name = "categories", referencedColumnName = "categoryid")就用:

@ManyToOne
private Categories categoryid;

在您的类别实体中添加：

@OneToMany(mappedBy="categoryid")
List<Products> products;

Select 在 Northwind 数据库上使用 JPA 和 JDBC 模板

Select on Northwind database using JPA and JDBC Template

spring-jdbc

jdbctemplate

spring-boot