Question

左外连接应该从左表中获取所有数据，无论是否存在来自B表的匹配记录，但是如果左表right_id列为空，则无法得到记录。

我正在解释更多

在数据模型中：Order.java，它是我的LEFT表，有一对一的关系

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

和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。

我发现了这个，

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表单，   也就是说，在from子句中显式使用join关键字。   这是推荐的表格。

隐式表单不使用join关键字。相反，   使用点符号对“关联”进行“解除引用”。隐式连接可以   出现在任何HQL子句中。内连接中的隐式连接结果   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 ";

因此，它工作，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

HQL Left Outer以一对一的关系连接空列

1 个答案: