流利的NHibernate一对多关系设置外键为null [英] Fluent NHibernate one-to-many relationship setting foreign key to null

问题描述

我有一个简单的流利NHibernate模型与两个相关的类：

 公共类申请人
 {
公共申请人（）
 {
 Tags =新列表< Tag>（）; 
} 
 
 public virtual int Id {get;组; } 
 
 //为了示例而删除了其他字段
 
公共虚拟IList< Tag>标签{get;保护组} 
 
 public virtual void AddTag（Tag tag）
 {
 tag.Applicant = this; 
 Tags.Add（tag）; 
 
 
 
 $ b $ public class Tag 
 {
 public virtual int Id {get;保护组} 
公共虚拟字符串TagName {get;组; } 
 
公共虚拟申请人申请人{get;组; } 
} 
  

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（）; 
 
 
 $ b $ public class TagMap：ClassMap< Tag> 
 {
 public TagMap（）
 {
 Id（x => x.Id）; 
 Map（x => x.TagName）; 
 
引用（x => x.Applicant）.Not.Nullable（）; 
 
 
 $ / code $ / pre 
 
 
每当我尝试更新申请人（插入一个新的工作正常），它失败了，我看到在日志中的以下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]错误NHibernate.AdoNet.AbstractBatcher-无法执行命令：UPDATE [Tag] SET Applicant_id = null WHERE Applicant_id = @ p0 System.Data.SqlClient.SqlException（0x80131904）：无法将NULL值插入'Applicant_id'列'RecruitmentApp .dbo.Tag';列不允许空值。更新失败。为什么NHibernate试图更新标签表并将Applicant_id设置为null？
 < 
解决方案 
设置 Applicant.Tags 到 Inverse 将指示NHibernate在申请人之后保存标签 
  public class ApplicantMap：ClassMap< Applicant> 
 {
 public ApplicantMap（）
 {
 Id（x => x.Id）; 
 
 HasMany（x => x.Tags）.Cascade.All（）。Inverse（）; 
 
 
 
 
 $ b更多详情：
 
 
 逆（而不是 .Not.Inverse（））意味着关系（在这种情况下，每个 Tag ）负责维护关系。因此，NHibernate知道必须首先保存 Applicant ，这样 Tag 对于它的<$ c有一个有效的外键$ c $> b 
 $ b 
经验法则：包含外键的实体通常是所有者，所以另一个表应该有反向 
 
I have a simple Fluent NHibernate model with two related classes:
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; }
}
My fluent mapping is the following:
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();
        }
    }
Whenever I try to update an applicant (inserting a new one works fine), it fails and I see the following SQL exception in the logs:
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.
Why is NHibernate trying to update the tag table and set Applicant_id to null? I'm at a loss on this one.
解决方案
Set Applicant.Tags to Inverse will instruct NHibernate to save Tags after the Applicant.
public class ApplicantMap : ClassMap<Applicant>
{
    public ApplicantMap()
    {
        Id(x => x.Id);

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

Inverse (as opposed to .Not.Inverse()) means the other side of the relationship (in this case, each Tag) is responsible for maintaining the relationship. Therefore, NHibernate knows that the Applicant must be saved first so that Tag has a valid foreign key for its Applicant.

Rule of thumb: The entity containing the foreign key is usually the owner, so the other table should have Inverse

                        
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