c# – NHibernate QueryOver将属性合并到另一个属性

概述考虑这个愚蠢的域名： namespace TryHibernate.Example{ public class Employee { public int Id { get; set; } public string Name { get; set; } } public class WorkItem { 考虑这个愚蠢的域名：

namespace TryHibernate.Example{    public class Employee    {        public int ID { get; set; }        public string name { get; set; }    }    public class WorkItem    {        public int ID { get; set; }        public string Description { get; set; }        public DateTime StartDate { get; set; }        public DateTime EndDate { get; set; }    }    public class Task    {        public int ID { get; set; }        public Employee Assignee { get; set; }        public WorkItem WorkItem { get; set; }        public string Details { get; set; }        public DateTime? StartDateOverrIDe { get; set; }        public DateTime? EndDateOverrIDe { get; set; }    }}

这个想法是每个工作项可能被分配给具有不同细节的多个员工,可能会覆盖工作项本身的开始/结束日期.如果这些覆盖为空,则应该从工作项中取出它们.

现在我想执行一个有效日期限制的查询.我先试过这个：

IList<Task> tasks = db.queryOver<Task>(() => taskAlias)    .JoinAlias(() => taskAlias.WorkItem,() => wiAlias)    .Where(() => taskAlias.StartDateOverrIDe.Coalesce(() => wiAlias.StartDate) <= end)    .And(() => taskAlias.EndDateOverrIDe.Coalesce(() => wiAlias.EndDate) >= start)    .List();

不幸的是,它没有编译,因为Coalesce期望一个常量,而不是属性表达式.

好的,我试过这个：

.Where(() => (taskAlias.StartDateOverrIDe == null                  ? wiAlias.StartDate                  : taskAlias.StartDateOverrIDe) <= end)    .And(() => (taskAlias.EndDateOverrIDe == null                  ? wiAlias.EndDate                  : taskAlias.EndDateOverrIDe) >= start)

这会抛出NullReferenceException.不知道为什么,但可能是因为NHibernate没有正确翻译那个三元运算符(并尝试实际调用它),或者因为== null不是检查空值的正确方法.无论如何,我甚至没想到它会起作用.

最后,这个工作：

IList<Task> tasks = db.queryOver<Task>(() => taskAlias)    .JoinAlias(() => taskAlias.WorkItem,() => wiAlias)    .Where(Restrictions.LeProperty(        Projections.sqlFunction("COALESCE",NHibernateUtil.DateTime,Projections.Property(() => taskAlias.StartDateOverrIDe),Projections.Property(() => wiAlias.StartDate)),Projections.Constant(end)))    .And(Restrictions.GeProperty(        Projections.sqlFunction("COALESCE",Projections.Property(() => taskAlias.EndDateOverrIDe),Projections.Property(() => wiAlias.EndDate)),Projections.Constant(start)))    .List();

但我无法称之为干净的代码.也许我可以将某些表达式提取到单独的方法中来清理它,但是使用表达式语法而不是这些丑陋的预测会好得多.有办法吗？ NHibernate背后是否有任何理由不支持Coalesce扩展中的属性表达式？

一个明显的选择是选择所有内容,然后使用linq或其他任何方式过滤结果.但它可能会成为一个总行数很多的性能问题.

这是完整的代码,以防有人想要尝试：

using (ISessionFactory sessionFactory = Fluently.Configure()    .Database(sqliteConfiguration.Standard.Usingfile("temp.sqlite").Showsql())    .MapPings(m => m.autoMapPings.Add(        autoMap.AssemblyOf<Employee>(new ExampleConfig())            .Conventions.Add(DefaultLazy.Never())            .Conventions.Add(DefaultCascade.All())))    .ExposeConfiguration(c => new SchemaExport(c).Create(true,true))    .BuildSessionFactory()){    using (ISession db = sessionFactory.OpenSession())    {        Employee empl = new Employee() { name = "Joe" };        WorkItem wi = new WorkItem()        {            Description = "important work",StartDate = new DateTime(2016,01,01),EndDate = new DateTime(2017,01)        };        Task task1 = new Task()        {            Assignee = empl,WorkItem = wi,Details = "Do this",};        db.Save(task1);        Task task2 = new Task()        {            Assignee = empl,Details = "Do that",StartDateOverrIDe = new DateTime(2016,7,1),EndDateOverrIDe = new DateTime(2017,1,};        db.Save(task2);        Task taskAlias = null;        WorkItem wiAlias = null;        DateTime start = new DateTime(2016,1);        DateTime end = new DateTime(2016,6,30);        IList<Task> tasks = db.queryOver<Task>(() => taskAlias)            .JoinAlias(() => taskAlias.WorkItem,() => wiAlias)            // This doesn't compile:            //.Where(() => taskAlias.StartDateOverrIDe.Coalesce(() => wiAlias.StartDate) <= end)            //.And(() => taskAlias.EndDateOverrIDe.Coalesce(() => wiAlias.EndDate) >= start)            // This throws NullReferenceException:            //.Where(() => (taskAlias.StartDateOverrIDe == null ? wiAlias.StartDate : taskAlias.StartDateOverrIDe) <= end)            //.And(() => (taskAlias.EndDateOverrIDe == null ? wiAlias.EndDate : taskAlias.EndDateOverrIDe) >= start)            // This works:            .Where(Restrictions.LeProperty(                Projections.sqlFunction("COALESCE",Projections.Constant(end)))            .And(Restrictions.GeProperty(                Projections.sqlFunction("COALESCE",Projections.Constant(start)))            .List();        foreach (Task t in tasks)            Console.Writeline("Found task: {0}",t.Details);    }}

配置非常简单：

class ExampleConfig : DefaultautomapPingConfiguration{    public overrIDe bool ShouldMap(Type type)    {        return type.namespace == "TryHibernate.Example";    }}

解决方法 让我们从这开始：

// This doesn't compile://.Where(() => taskAlias.StartDateOverrIDe.Coalesce(() => wiAlias.StartDate) <= end)//.And(() => taskAlias.EndDateOverrIDe.Coalesce(() => wiAlias.EndDate) >= start)

并将其修改为：

.Where(() => taskAlias.StartDateOverrIDe.Coalesce(wiAlias.StartDate) <= end).And(() => taskAlias.EndDateOverrIDe.Coalesce(wiAlias.EndDate) >= start)

现在它将编译.但在运行时它会生成相同的NullReferenceException.不好.

事实证明,NHibernate确实试图评估Coalesce论证.通过查看ProjectionExtensions类实现可以很容易地看到这一点.以下方法处理Coalesce转换：

internal static IProjection ProcessCoalesce(MethodCallExpression methodCallExpression){  IProjection projection = ExpressionProcessor.FindMemberProjection(methodCallExpression.Arguments[0]).AsProjection();  object obj = ExpressionProcessor.FindValue(methodCallExpression.Arguments[1]);  return Projections.sqlFunction("coalesce",(IType) NHibernateUtil.Object,projection,Projections.Constant(obj));}

注意第一个参数(FindMemberExpresion)与第二个参数(FindValue)的不同处理.好吧,FindValue只是试图评估表达式.

现在我们知道造成这个问题的原因了.我不知道为什么会这样实现,所以将集中精力寻找解决方案.

幸运的是,ExpressionProcessor类是公共的,并且还允许您通过RegisterCustomMethodCall / RegisterCustomProjection方法注册自定义方法.这导致我们解决方案：

>创建类似于Coalesce的自定义扩展方法(例如,将它们称为IfNull)
>注册自定义处理器
>使用它们而不是Coalesce

这是实施：

public static class CustomProjections{    static CustomProjections()    {        ExpressionProcessor.RegisterCustomProjection(() => IfNull(null,""),ProcessIfNull);        ExpressionProcessor.RegisterCustomProjection(() => IfNull(null,0),ProcessIfNull);    }    public static voID Register() { }    public static T IfNull<T>(this T objectProperty,T replaceValueIfIsNull)    {        throw new Exception("Not to be used directly - use insIDe queryOver Expression");    }    public static T? IfNull<T>(this T? objectProperty,T replaceValueIfIsNull) where T : struct    {        throw new Exception("Not to be used directly - use insIDe queryOver Expression");    }    private static IProjection ProcessIfNull(MethodCallExpression mce)    {        var arg0 = ExpressionProcessor.FindMemberProjection(mce.Arguments[0]).AsProjection();        var arg1 = ExpressionProcessor.FindMemberProjection(mce.Arguments[1]).AsProjection();        return Projections.sqlFunction("coalesce",NHibernateUtil.Object,arg0,arg1);    }}

由于从不调用这些方法,因此需要通过调用Register方法来确保注册自定义处理器.这是一个空方法,只是为了确保调用类的静态构造函数,实际的注册发生在那里.

所以在你的例子中,包括在开头：

CustomProjections.Register();

然后在查询中使用：

.Where(() => taskAlias.StartDateOverrIDe.IfNull(wiAlias.StartDate) <= end).And(() => taskAlias.EndDateOverrIDe.IfNull(wiAlias.EndDate) >= start)

它将按预期工作.

附：上面的实现适用于常量和表达式参数,因此它实际上是Coalesce的安全替代品.

总结

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