java - 实现多个表的 JOIN

Question

我有这个表，我想从中选择许多行并使用 JOIN 将 id 转换为两个表中的名称。我试过这个:

主表:

@Entity
@Table(name = "payment_transactions")
public class PaymentTransactions implements Serializable {
    ..... 
    @Column(length = 4)
    private Integer merchant_id;

    @Column(length = 4)
    private Integer terminal_id; 
    ......
}

包含附加数据的表格:

@Entity
@Table(name = "merchants")
public class Merchants implements Serializable {

    @Column(name = "id")
    private int id;

    @Column(length = 255)
    private String name;
    .........
}


@Entity
@Table(name = "terminals")
public class Terminals implements Serializable {

    @Column(name = "id")
    private int id;

    @Column(length = 255)
    private String name;
    .........
}

我尝试过这个:

String hql = "select e.* from " + PaymentTransactions.class.getName() + " e "
                + " INNER JOIN " + Merchants.class.getName() + " m "
                + " ON e.id = m.merchant_id AND " 
                + " INNER JOIN " + Terminals.class.getName() + " t "
                + " ON e.id = t.terminal_id "
                + " where e.created_at >= :start_date and e.created_at <= :end_date";

总体思路是，我想要一个主表Payment transactions，它将merchant_id和terminal_id存储为数字。通过加入，我想获取商家和终端的名称。实现这个的正确方法是什么？

Answer 1

您只需将这些变量添加到查询中的列列表中即可:

String hql = "select e.*, m.name AS merchant, t.name AS terminal"
                + " FROM " + PaymentTransactions.class.getName() + " e "
                + " INNER JOIN " + Merchants.class.getName() + " m "
                + " ON e.id = m.merchant_id AND " 
                + " INNER JOIN " + Terminals.class.getName() + " t "
                + " ON e.id = t.terminal_id "
                + " where e.created_at >= :start_date and e.created_at <= :end_date";

请注意，您需要添加列别名以避免输出结果中出现两次相同的列名称 (name)。查询包含这些内容(例如 m.name ASmerchant)，以便您在获取结果时可以将商家名称作为 merchant 列进行访问。