如何使用 NHibernate 将派生属性映射到基类上？

Question

我在某些映射方面遇到问题。假设我有三个评估，它们都源自基础 Assessment：换句话说

public abstract class Assessment
{
    public abstract int DamageCostTotal { get; set; }
}

public class IndividualAssessment
{
    public virtual int DamageCostHouse { get; set; }
    public virtual int DamageCostCar { get; set; }
    public virtual int DamageCostBelongings { get; set; }
    public override DamageCostTotal
    {
        get { return DamageCostHouse + DamageCostCar + DamageCostBelongings; }
    }
}

public class BusinessAssessment
{
    public virtual int DamageCostBuilding { get; set; }
    public virtual int DamageCostGoods { get; set; }
    public virtual int DamageCostOther { get; set; }
    public override DamageCostTotal
    {
        get { return DamageCostBuilding + DamageCostGoods + DamageCostOther; }
    }
}

public class InfrastructureAssessment
{
    public virtual int DamageCostStructure { get; set; }
    public virtual int DamageCostEstimatedRepair { get; set; }
    public override DamageCostTotal
    {
        get { return DamageCostStructure + DamageCostEstimatedRepair; }
    }
}

，三种评估类型：IndividualAssessment、BusinessAssessment 和 < code>InfrastructuralAssessment，都有特定的损坏成本，但它们都实现了基类的 DamageTotalCost 以获得一项评估的总损坏成本。

在我的 Fluent NHibernate 映射中，我为每个特定评估映射了每个 DamageCostTotal：

// individual assessment
Map(x => x.DamageCostTotal)
    .Access.Readonly()
    .Formula("DamageCostHouse + DamageCostCar + DamageCostBelongings");
// the other two are mapped the same way, just with a different formula

当我查询特定评估类型时，这非常有效：

Session.Query<IndividualAssessment>().OrderBy(x => x.DamageCostTotal);
Session.Query<BusinessAssessment>().OrderBy(x => x.DamageCostTotal);
Session.Query<InfrastructureAssessment>().OrderBy(x => x.DamageCostTotal);

但是当我尝试查询基本评估类型时：

Session.Query<Assessment>().OrderBy(x => x.DamageCostTotal);

它会生成错误的 SQL（为更容易阅读）：

SELECT ...
    DamageCostHouse + DamageCostCar + DamageCostBelongings as formula0_0_,
    DamageCostBuilding + DamageCostGoods + DamageCostOther as formula1_0_,
    DamageCostStructure + DamageCostEstimatedRepair as formula2_0_,
    FROM [Assessment] this_
    ORDER BY DamageCostStructure + DamageCostEstimatedRepair

如您所见，它正确创建了公式，但是当它执行 ORDER BY 时，它仅按 InfrastructuralAssessment 属性而不是公式进行排序。有谁知道如何映射基本 DamageCostTotal 以便此查询返回正确的结果？

Answer 1

一种解决方案是将 DamageCostTotal 映射到基类中。如果表中没有 DamageCostTotal 列，则创建一列。 NHibernate 不需要了解这种情况下的公式，这很好，因为这些类已经在承担繁重的工作。

您的查询应该生成与此类似的 SQL...

SELECT ..., this_.DamageCostTotal FROM Assessment this_ ORDER BY this_.DamageCostTotal