NHibernate HQL Generator支持SQL Server 2016时态表 [英] NHibernate HQL Generator to support SQL Server 2016 temporal tables

问题描述

我正在尝试在NHibernate 4.x中实现对SQL Server 2016时态表的基本支持.想法是从

I am trying to implement basic support for SQL Server 2016 temporal tables in NHibernate 4.x. The idea is to alter SQL statement from

SELECT * FROM Table t0

到

SELECT * FROM Table FOR SYSTEM_TIME AS OF '2018-01-16 00:00:00' t0

您可以在SQL Server 2016中找到有关时态表的更多信息

You can find more info about temporal tables in SQL Server 2016 here

不幸的是，我没有找到在表名及其别名之间插入FOR FOR SYSTEM_TIME AS OF '...'语句的任何方法.我不确定自定义方言是否支持此功能.我目前唯一可行的解​​决方案是将FOR SYSTEM_TIME语句附加到额外的WHERE中，并且我的输出SQL看起来像这样

Unfortunately, I've not found any way to insert FOR FOR SYSTEM_TIME AS OF '...' statement between table name and its alias. I'm not sure if custom dialects supports this. The only working solution I have for now is to append FOR SYSTEM_TIME statement within extra WHERE and my output SQL looks like this

SELECT * FROM Table t0 WHERE FOR SYSTEM_TIME AS OF '2018-01-16 00:00:00'=1

为此，我实现了生成器和方言，如下所示:

To do so, I have implemented generator and dialect as follows:

public static class AuditableExtensions
{
    public static bool AsOf(this IAuditable entity, DateTime date)
    {
        return true;
    }

    public static IQueryable<T> Query<T>(this ISession session, DateTime asOf) where T : IAuditable
    {
        return session.Query<T>().Where(x => x.AsOf(asOf));
    }
}

public class ForSystemTimeGenerator : BaseHqlGeneratorForMethod
{
    public static readonly string ForSystemTimeAsOfString = "FOR SYSTEM_TIME AS OF";

    public ForSystemTimeGenerator()
    {
        SupportedMethods = new[]
        {
            ReflectionHelper.GetMethod(() => AuditableExtensions.AsOf(null, DateTime.MinValue))
        };
    }

    public override HqlTreeNode BuildHql(MethodInfo method, Expression targetObject, 
        ReadOnlyCollection<Expression> arguments,
        HqlTreeBuilder treeBuilder, 
        IHqlExpressionVisitor visitor)
    {
        return treeBuilder.BooleanMethodCall(nameof(AuditableExtensions.AsOf), new[]
        {
            visitor.Visit(arguments[1]).AsExpression()
        });
    }
}

public class MsSql2016Dialect : MsSql2012Dialect
{
    public MsSql2016Dialect()
    {
        RegisterFunction(nameof(AuditableExtensions.AsOf), new SQLFunctionTemplate(
            NHibernateUtil.Boolean, 
            $"{ForSystemTimeGenerator.ForSystemTimeAsOfString} ?1?2=1"));
    }
}

任何人都可以提供任何更好的方法或示例，以便继续使用并在表名及其别名之间插入FOR SYSTEM_TIME AS OF语句吗?目前，我唯一能看到的解决方案是在SessionInterceptor中的OnPrepareStatement中更改SQL，但是我相信有一些更好的方法...

Can anyone provide any better approach or samples I could use to move forward and insert FOR SYSTEM_TIME AS OF statement between table name and its alias? At this moment the only solution I can see is to alter SQL in OnPrepareStatement in SessionInterceptor but I believe there is some better approach...

推荐答案

在第19.1节中的示例显示了如何使用时间表:

The example in section 19.1 shows how to use temporal tabvles:

首先定义一个过滤器:

<filter-def name="effectiveDate">
<filter-param name="asOfDate" type="date"/>
</filter-def>

然后将其附加到课程:

<class name="Employee" table="Employee For System_Time All" ...>
   ...
   <many-to-one name="Department" column="dept_id" class="Department"/>
   <property name="EffectiveStartDate" type="date" column="eff_start_dt"/>
   <property name="EffectiveEndDate" type="date" column="eff_end_dt"/>
   ...
   <!--
   Note that this assumes non-terminal records have an eff_end_dt set to
   a max db date for simplicity-sake
   -->
   <filter name="effectiveDate"
   condition=":asOfDate BETWEEN eff_start_dt and eff_end_dt"/>
</class>

然后，您需要在会话上启用过滤器:

Then you need to enable the filter on the session:

   ISession session = ...;
   session.EnableFilter("effectiveDate").SetParameter("asOfDate", DateTime.Today);
   var results = session.CreateQuery("from Employee as e where e.Salary > :targetSalary")
   .SetInt64("targetSalary", 1000000L)
   .List<Employee>();

希望这可以使人们入门.

Hope this gets people started.

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