NHibernate HQL 内连接 (SQL Server,Visual C#)

Question

我想将 HQL 与内部联接一起使用。但是，会引发查询语法异常。

这是我的 C# 代码：

string sqlQuery = "Select fq FROM Answers as fq INNER JOIN Questions as q " +
    " on fq.questionId=q.questionId";

IList Result;
int count = 0;

try
{
    using (ISession session = ConnectionModule.OpenSession())
    {
        IQuery query = session.CreateQuery(sqlQuery);
        session.CreateCriteria(typeof(Answers));
        Result = query.List();
    }
}
catch(Exception ex) 
{
    MessageBox.Show(ex.Message+"\n"+ex.InnerException);
}

Answer 1

这里的重点是

• 如果没有映射关系，则进行交叉连接，
• 加入现有（映射）关系。

所以，如果没有映射关系 Question 到 Answer - 我们仍然可以像这样查询它：

// instead of INNER JOIN we use 'comma' to produce CROSS JOIN
// instead of ON we need WHERE
// string sqlQuery = "Select fq FROM Answers as fq, INNER JOIN Questions as q "+ 
//  "on fq.questionId=q.questionId";

string sqlQuery = "Select fq FROM Answers as fq, Questions as q " +
    " WHERE fq.questionId=q.questionId";

如果我们有映射 Answer.Question 和 IList<Answer> Question.Answers

// the Reference (C#) is the way how to express ON
string sqlQuery = "Select fq FROM Answers as fq INNER JOIN fq.Questions as q";

检查

• 14.2. The from clause （关于 CROSS JOIN 的详细信息）
• 14.3. Associations and joins （与引用相关的标准 JOIN）