我在让 NHibernate 生成一个实际运行没有错误的 SQL 查询时遇到问题,因为该查询缺少我的子类的连接。
让我们举这个最小的例子:
class Page
{
public virtual int Id { get; set; }
public virtual string UrlSegment { get; set;}
public virtual Page Parent { get; set; }
}
class ContentPage
{
public string Content { get; set; }
}
现在,想象一个直接的字段对字段、连接子类的映射到数据库。我想出了这个查询来查找路径 /page/page2/page3 上的所有页面:
SELECT p1.* FROM page p1
WHERE
p1.parent IS NULL
AND p1.hierarchysegment = 'test'
UNION
SELECT p2.* FROM page p1
JOIN page p2 ON p2.parent = p1.id
WHERE
p1.parent IS NULL
AND p1.hierarchysegment = 'test'
AND p2.hierarchysegment = 'test2'
UNION
SELECT p3.* FROM page p1
JOIN page p2 ON p2.parent = p1.id
JOIN page p3 ON p3.parent = p2.id
WHERE
p1.parent IS NULL
AND p1.hierarchysegment = 'test'
AND p2.hierarchysegment = 'test2'
AND p3.hierarchysegment = 'test3'
;
现在,这在运行查询时似乎可以正常工作。让我们尝试使用 SqlQuery 生成它(简化,仅显示第一部分):
IQuery q = session.CreteSQLQuery("SELECT {p0.*} FROM page {p0} WHERE {p0.Parent} IS NULL" +
"AND {p0.HierarchySegment} = 'page1'", "p0", typeof(Page));
这会生成以下查询:
SELECT p0.ID AS id0_0_,
p0.enabled AS enabled0_0_,
p0.linktext AS linktext0_0_,
p0.hierarchysegment AS hierarch4_0_0_,
p0.tooltiptext AS tooltipt5_0_0_,
p0.PARENT AS parent0_0_,
p0_1_.content AS content1_0_,
CASE
WHEN p0_1_.ID IS NOT NULL
THEN 1
WHEN p0.ID IS NOT NULL
THEN 0
END AS clazz_0_
FROM page p0
WHERE parent0_0_ IS NULL
AND hierarch4_0_0_ = page1;
但是这个查询包含 SQL 错误,因为 NHibernate 试图获取只有在 NHibernate 还为子类 ContentPage 添加连接之后才可用的字段。是否可以在不依赖 NHibernate 恰好使用的特定命名样式的情况下以某种方式添加这些连接(即,手动生成必要的连接)?