流畅的NHibernate一对多关系将外键设置为null

Question

我有一个简单的Fluent NHibernate模型,有两个相关的类:

public class Applicant
    {
        public Applicant()
        {
            Tags = new List<Tag>();
        }

        public virtual int Id { get; set; }

        //other fields removed for sake of example

        public virtual IList<Tag> Tags { get; protected set; }

        public virtual void AddTag(Tag tag)
        {
            tag.Applicant = this;
            Tags.Add(tag);
        }
    }


public class Tag
{
    public virtual int Id { get; protected set; }
    public virtual string TagName { get; set; }

    public virtual Applicant Applicant { get; set; }
}

我的流利映射如下:

public class ApplicantMap : ClassMap<Applicant>
    {
        public ApplicantMap()
        {
            Id(x => x.Id);

            HasMany(x => x.Tags).Cascade.All();
        }
    }

    public class TagMap : ClassMap<Tag>
    {
        public TagMap()
        {
            Id(x => x.Id);
            Map(x => x.TagName);

            References(x => x.Applicant).Not.Nullable();
        }
    }

每当我尝试更新申请人(插入一个新的工作正常),它失败,我在日志中看到以下SQL异常:

11:50:52.695 [6] DEBUG NHibernate.SQL - UPDATE [Tag] SET Applicant_id = null WHERE Applicant_id = @p0;@p0 = 37 [Type: Int32 (0)] 
11:50:52.699 [6] ERROR NHibernate.AdoNet.AbstractBatcher - Could not execute command: UPDATE [Tag] SET Applicant_id = null WHERE Applicant_id = @p0 System.Data.SqlClient.SqlException (0x80131904): Cannot insert the value NULL into column 'Applicant_id', table 'RecruitmentApp.dbo.Tag'; column does not allow nulls. UPDATE fails.

为什么NHibernate会尝试更新标记表并将Applicant_id设置为null？我对此感到茫然.

Answer 1

设置Applicant.Tags为Inverse将指示NHibernate保存Tags后Applicant.

public class ApplicantMap : ClassMap<Applicant>
{
    public ApplicantMap()
    {
        Id(x => x.Id);

        HasMany(x => x.Tags).Cascade.All().Inverse();
    }
}

更多详情:

Inverse(相对于.Not.Inverse())意味着关系的另一方(在这种情况下,每个Tag)负责维持关系.因此,NHibernate知道Applicant必须先保存,以便Tag有一个有效的外键Applicant.

经验法则:包含外键的实体通常是所有者,因此另一个表应具有 Inverse