流畅的NHibernate:如何创建一对多双向映射？

Question

基本问题:如何在Fluent NHibernate中创建双向一对多地图？

细节:

我有一个有很多孩子的父对象.在我的情况下,孩子没有父母,所以在数据库中,我想外键的母体有NOT NULL约束是没有意义的.我从Fluent NHibernate映射自动生成我的数据库.

我的父母有很多子对象,如下所示:

public class Summary
{
   public int id {get; protected set;}

   public IList<Detail> Details {get; protected set;}
}

public  class Detail
{
   public int id {get; protected set;}

   public string ItemName {get; set;}

  /* public Summary Owner {get; protected set;} */ //I think this might be needed for bidirectional mapping?
}

这是我开始的映射:

public class SummaryMap : ClassMap<Summary>
{
    public SummaryMap()
    {
        Id(x => x.ID);

        HasMany<Detail>(x => x.Details);
    }
}

public class DetailMap : ClassMap<Detail>
{
    public DetailMap()
    {
        Id(x => x.ID);

        Map(x => x.ItemName).CanNotBeNull();
    }
}

在详细信息表中,Summary_id应该是不为空,因为在我的情况下,它是没有意义的,不附加摘要对象的明细对象.但是,只使用HasMany()映射使得Summary_id外键可以为空.

我在NHibernate的文档(发现http://www.hibernate.org/hib_docs/nhibernate/html/collections.html)认为,"如果父亲是必须的,可以使用双向one-to-many关联".

那么如何在Fluent NHibernate中创建双向一对多地图？

Answer 1

要在Details表中获得与非null外键列的双向关联,您可以在DetailsMap类中添加建议的Owner属性,References(...).CanNotBeNull()映射,并使Summary结束.

要避免为两个关联方向指定两个不同的外键列,可以手动指定列名,也可以为两个方向指定相同列名的方式命名属性.在这种情况下,我建议您将Details.Owner属性重命名为Details.Summary.

我通过增量生成了Summary id,以避免在插入表时出现问题,因为Summary currenty除了id之外没有列.

域:

public class Detail
{
    public int id { get; protected set; }
    public string ItemName { get; set; }

    // Renamed to use same column name as specified in the mapping of Summary.Details
    public Summary Summary {get; set;} 
}

public class Summary
{
    public Summary()
    {
        Details = new List<Detail>();
    }

    public int id { get; protected set; }
    public IList<Detail> Details { get; protected set; }
}

制图:

public class DetailMap : ClassMap<Detail>
{
    public DetailMap()
    {
        Id(x => x.id)
            .GeneratedBy.Native();

        Map(x => x.ItemName)
            .CanNotBeNull();

        References<Summary>(x => x.Summary)
            // If you don't want to rename the property in Summary,
            // you can do this instead:
            // .TheColumnNameIs("Summary_id")
            .CanNotBeNull();
    }
}

public class SummaryMap : ClassMap<Summary>
{
    public SummaryMap()
    {
        Id(x => x.id)
            .GeneratedBy.Increment();

        HasMany<Detail>(x => x.Details)
            .IsInverse()
            .AsBag(); // Use bag instead of list to avoid index updating issues
    }
}