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java - 从查询中获取结果作为自定义对象列表

问题描述

我想为显示过去 10 天每天的交易量的条形图实现 SQL 查询。例如我有这个表结构：

CREATE TABLE `payment_transactions` (
  `id` int(11) NOT NULL,
  `amount` int(11) DEFAULT NULL,
  `created_at` datetime DEFAULT NULL,
  PRIMARY KEY (`id`),
);

我得到这个示例结果（每天分组）：

Date       | Amount| Number of transactions per day |
11-11-2018 | 30    | 3                              |
11-12-2018 | 230   | 13                             |

JPA 查询：

public List<DashboardDTO> findAll() {

        String hql = "SELECT date(created_at) AS cdate, sum(amount) AS amount, count(id) AS nooftransaction "
                + "FROM payment_transactions WHERE date(created_at)>=date(now()- interval 10 DAY) "
                + "AND date(created_at)<date(now()) GROUP BY date(created_at)";

        TypedQuery<DashboardDTO> query = entityManager.createQuery(hql, Merchants.class);
        List<DashboardDTO> data = query.getResultList();

        return data;
    }

Java 对象：

public class DashboardDTO {

    private Date date;
    private int amount;
    private int number_of_transactions;

    public DashboardDTO(Date date, int amount, int number_of_transactions) {
        this.date = date;
        this.amount = amount;
        this.number_of_transactions = number_of_transactions;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public int getAmount() {
        return amount;
    }

    public void setAmount(int amount) {
        this.amount = amount;
    }

    public int getNumber_of_transactions() {
        return number_of_transactions;
    }

    public void setNumber_of_transactions(int number_of_transactions) {
        this.number_of_transactions = number_of_transactions;
    }
}

如何正确实施查询？我想在List<DashboardDTO>不使用实体的情况下获得结果？

标签： javasqljpaspring-data-jpa

解决方案

简单的方法是将@Entity,添加@Id到您DashboardDTO的本地 sql 别名中，并使您的本地 sql 别名与 DTO 的属性名称匹配。

@Entity
public class DashboardDTO {
  @Id
  private Date cdate;
  private int amount;
  private int numberOfTransactions;
  ...
}

public List<DashboardDTO> findAll() {
  String hql = "SELECT ... AS cdate, ... AS amount, ... AS number_of_transactions FROM ...";
  return entityManager.createNativeQuery(hql, DashboardDTO.class).getResultList();
}

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