一对一关系中空列的HQL左外连接

Question

无论B表是否有匹配记录，左外连接都应该从左表获取所有数据，但是如果左表right_id列为空，则无法获取记录。

我在解释更多

在数据模型中：Order.java，是我的LEFT表，是一对一的关系

@OneToOne(targetEntity = OrderShippingDetail.class, optional=true, cascade = {CascadeType.ALL})
@JoinColumn(name = "SHIPPING_DETAIL_ID", referencedColumnName = "ID")
private OrderShippingDetail shippingDetail;

HQL 是：

    hql = "SELECT " +
            "o.id as id, " +
            "o.createTime as createTime, " +
            "o.customerEmailAddress as customerEmailAddress, " +
            "o.customerPhoneNumber as customerPhoneNumber, " +
            "o.customerNote as customerNote, " +
            "o.invoicePrintedFlag as invoicePrintedFlag, " +
            "shippingAddress.address.personName as shippingPersonName, " +
            "shippingDetail.shippingCompany.id as shippingCompanyId, "+
            "shippingDetail.shippingCompany.name as shippingCompanyName, "+
            "shippingDetail.receiptNumber as shippingReceiptNumber, "+
            "shippingDetail.trackingNumber as shippingTrackingNumber, "+
            "shippingDetail.price as shippingPrice, "+
            "o.invoiceNumber as invoiceNumber " + 
        "FROM Order AS o " +
        "LEFT OUTER JOIN o.shippingAddress AS shippingAddress " +
        "LEFT OUTER JOIN o.shippingDetail AS shippingDetail ";

但是只有“SHIPPING_DETAIL_ID”不为空的记录。 HQL 有错误吗？它是通过建模 SQL 命令创建的，该命令是在 hibernate 运行时自动创建的。

我找到了，

HQL 支持两种形式的关联加入：隐式和显式。

上一节中显示的查询都使用显式形式， 也就是说，在 from 子句中显式使用了 join 关键字。 这是推荐的形式。

隐式形式不使用 join 关键字。相反， 使用点符号“取消引用”关联。隐式连接可以 出现在任何 HQL 子句中。隐式连接导致内部连接 在生成的 SQL 语句中。

我删除了 SELECT 部分中的点符号，所以我的新 HQL：

hql = "SELECT " +
                "o.id as id, " +
                "o.createTime as createTime, " +
                "o.customerEmailAddress as customerEmailAddress, " +
                "o.customerPhoneNumber as customerPhoneNumber, " +
                "o.customerNote as customerNote, " +
                "o.invoicePrintedFlag as invoicePrintedFlag, " +
                "shippingDetail, " +
                "o.invoiceNumber as invoiceNumber " + 
            "FROM Order AS o " +
            "LEFT OUTER JOIN o.shippingAddress AS shippingAddress " +
            "LEFT OUTER JOIN o.shippingDetail AS shippingDetail ";

所以，它有效，它返回 Order 表中的所有记录，但是，我不想选择 ShippingDetail 对象中的所有列和关系。我该怎么做才能解决这个问题？

Answer 1

在查询中添加另一个显式左连接：

SELECT o.id as id, 
...,
shippingCompany.id as shippingCompanyId, 
shippingCompany.name as shippingCompanyName, 
...
FROM Order AS o
LEFT OUTER JOIN o.shippingAddress AS shippingAddress 
LEFT OUTER JOIN o.shippingDetail AS shippingDetail
LEFT OUTER JOIN shippingDetail.shippingCompany AS shippingCompany