NHibernate 投影查询

Question

我有两个实体 A 和 B，其中 A 与 B 具有一对多关系。我想创建一个 NHibernate 查询来获取所有 A 实体和所有 B 记录，其中：

A 实体处于活动状态
获取的 B 个实体在一个日期范围内（我有 2 个 c# DateTime 个对象）。

实体A
+----+--------+
|编号 |活跃|
+----+--------+
| 1 | 1 |
| 2 | 0 |
| 3 | 1 |
+----+--------+

实体B
+----+--------+--------+------------+
|编号 |年份 |月 | foreign_id |
+----+--------+--------+------------+
| 1 | 2000 | 11 | 1 |
| 2 | 2001 | 12 | 2 |
| 3 | 2002 | 4 | 1 |
+----+--------+--------+------------+

到目前为止我试过这个：

return this.sessionFactory.GetCurrentSession()
    .QueryOver<A>()
    .Where(x => x.Active)
    .JoinQueryOver(x => x.BList)
    .WhereRestrictionOn(y => y.Year * 12 + y.Month) // the problem is here, exception below
    .IsBetween(2000 * 12 + 1) // january 2000
    .And(2010 * 12 + 3) // march 2010
    .List();

System.InvalidOperationException: variable 'x' of type 'Domain.A' referenced from scope '', but it is not defined

一般来说，我不喜欢以月数计算所有日期的方法（我的应用程序不关心天数、小时数等...）但是，我不想更改我的映射现在（如下所示）。

我需要一些帮助来修复这段代码，或者建议我怎样才能做得更好（或者两者都更好）。

更多详情：

我的 c# 实体如下所示：

public class A
{
    public virtual int Id { get; set; }
    public virtual int Active { get; set; }
    public virtual IEnumerable<B> BList { get; set; }
}


public class B
{
    public virtual int Month { get; set; }
    public virtual int Year { get; set; }
}


internal class AMapping: ClassMap<A>
{
    public AMapping()
    {
        Table("AObjects");

        Id(x => x.Id, "id");
        Map(x => x.Active, "active");

        HasMany(x => x.BList)
            .Table("Bobjects")
            .KeyColumn("foreign_id")
            .Component(y => {
                  y.Map(b => b.Month, "month");
                  y.Map(b => b.Year, "year");
        });
    }
}

Answer 1

我认为一种方法是使用过滤器。首先要做的是通过过滤器 class 创建过滤器定义，如下所示：

public class MonthsFilter : FilterDefinition
{
    public MonthsFilter()
    {
        WithName("MonthsFilter")
            .AddParameter("startMonths", NHibernateUtil.Int32)
            .AddParameter("endMonths", NHibernateUtil.Int32);
    }
}

然后您需要通过 ApplyFilter 方法将过滤器添加到您的 ClassMap for A，添加到 BList 属性：

internal class AMapping : ClassMap<A>
{
    public AMapping()
    {
        Table("AObjects");

        Id(x => x.Id, "id");
        Map(x => x.Active, "active");

        HasMany(x => x.BList)
            .Table("BObjects")
            .KeyColumn("foreign_id")
            .Component(y => {
                y.Map(b => b.Month, "month");
                y.Map(b => b.Year, "year");
            }).ApplyFilter<MonthsFilter>("year * 12 + month BETWEEN :startMonths and :endMonths");
    }
}

最后，您需要在发出查询之前启用过滤器，类似于：

using (var session = sessionFactory.OpenSession())
{
    // Enable filter and pass parameters
    var startMonthsValue = 2000 * 12 + 1;    // january 2000
    var endMonthsValue = 2010 * 12 + 3;  // march 2010
    session.EnableFilter("MonthsFilter")
        .SetParameter("startMonths", startMonthsValue)
        .SetParameter("endMonths", endMonthsValue);

    // Create and execute query (no filter for B needed here)
    var list = session.QueryOver<A>()
        .Fetch(x => x.BList).Eager  // Eager fetch to avoid the N+1 problem due to BList lazy load
        .Where(x => x.Active)
        .TransformUsing(Transformers.DistinctRootEntity)    // List only distinct A entities, to avoid duplicated entries due to eager fetch one-to-many relation
        .List();

    // Do whatever you want with the results
    foreach (var item in list)
    {
        Console.WriteLine("A id: {0} - B children count: {1}", item.Id, item.BList.Count());
    }
}

一个完整的工作示例：

using FluentNHibernate.Cfg;
using FluentNHibernate.Cfg.Db;
using FluentNHibernate.Mapping;
using NHibernate;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

namespace NHibernateTests
{
    public class A
    {
        public virtual int Id { get; set; }
        public virtual bool Active { get; set; }
        public virtual IEnumerable<B> BList { get; set; }
    }


    public class B
    {
        public virtual int Month { get; set; }
        public virtual int Year { get; set; }
    }


    internal class AMapping : ClassMap<A>
    {
        public AMapping()
        {
            Table("AObjects");

            Id(x => x.Id, "id");
            Map(x => x.Active, "active");

            HasMany(x => x.BList)
                .Table("BObjects")
                .KeyColumn("foreign_id")
                .Component(y => {
                    y.Map(b => b.Month, "month");
                    y.Map(b => b.Year, "year");
                }).ApplyFilter<MonthsFilter>("year * 12 + month BETWEEN :startMonths and :endMonths");
        }
    }

    public class MonthsFilter : FilterDefinition
    {
        public MonthsFilter()
        {
            WithName("MonthsFilter")
                .AddParameter("startMonths", NHibernateUtil.Int32)
                .AddParameter("endMonths", NHibernateUtil.Int32);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var sessionFactory = CreateNHibernateSessionFactory();
            using (var session = sessionFactory.OpenSession())
            {
                // Enable filter and pass parameters
                var startMonthsValue = 2000 * 12 + 1;    // january 2000
                var endMonthsValue = 2010 * 12 + 3;  // march 2010
                session.EnableFilter("MonthsFilter")
                    .SetParameter("startMonths", startMonthsValue)
                    .SetParameter("endMonths", endMonthsValue);

                // Create and execute query (no filter needed here)
                var list = session.QueryOver<A>()
                    .Fetch(x => x.BList).Eager  // Eager fetch to avoid the N+1 problem due to BList lazy load
                    .Where(x => x.Active)
                    .TransformUsing(Transformers.DistinctRootEntity)    // List only distinct A entities, to avoid duplicated entries due to eager fetch one-to-many relation
                    .List();

                // Do whatever you want with the results
                foreach (var item in list)
                {
                    Console.WriteLine("A id: {0} - B children count: {1}", item.Id, item.BList.Count());
                }
            }

            Console.WriteLine("Press ENTER to continue...");
            Console.ReadLine();
        }

        static ISessionFactory CreateNHibernateSessionFactory()
        {
            FluentConfiguration fc = Fluently.Configure()
                .Database(MsSqlConfiguration.MsSql2012.ConnectionString("Server=.\SQLEXPRESS;Database=NHibernateTests;Trusted_Connection=True;"))
                .Mappings(m => {
                    m.FluentMappings
                        .AddFromAssembly(Assembly.GetExecutingAssembly());
                });

            var config = fc.BuildConfiguration();

            return config.SetProperty(NHibernate.Cfg.Environment.ReleaseConnections, "on_close")
                       .BuildSessionFactory();
        }
    }
}

有关过滤器的更多信息：

NHibernate docs - Chapter 20. Filtering data
NHibernate - Retrieve parent / children with criteria applied only to children
Syntax to define a NHibernate Filter with Fluent Nhibernate?

Answer 2

从 NHibernate 5.3 开始支持 QueryOver lambda 内部的计算。所以

.WhereRestrictionOn(y => y.Year * 12 + y.Month)

应该按原样工作。

NHibernate 投影查询

NHibernate query over projection

c#

.net

nhibernate

fluent-nhibernate

queryover