多对多映射，联接表中有额外的列 [英] Many-to-many mapping with extra columns in join table

问题描述

这是我希望拥有的域:

public class Person
{
    public int Id { get; set; }
    public IList<AcquiredCertificate> AcquiredCertificates { get; set; }
}

public class AcquiredCertificate
{
    public Person Acquirer { get; set; }
    public Certificate Certificate { get; set; }
    public DateTime DateAcquired;
}

public class Certificate
{
    public int Id { get; set; }     
}

这是我拥有的架构:

CREATE TABLE People (
    PersonId INT PRIMARY KEY
);

CREATE TABLE Certificates (
    CertificateId INT PRIMARY KEY
);

CREATE TABLE CertificatesAcquiredByPeople (
    PersonId INT,
    CertificatedId INT,
    DateAcquired DATETIME
);

这是人为设计的架构和域，但与我正在使用的东西几乎相同.我目前正在通过编写第三个域实体来表示CertificatesAcquiredByPeople表来进行工作，但这对我来说真的很奇怪.

It's a contrived schema and domain but it's pretty much the same as something that I am working with. I currently have it working by writing a 3rd domain entity to represent the CertificatesAcquiredByPeople table but that really seems strange to me.

我该如何使用NHibernate映射它?我相信hbm文件中的component标签应该可以实现我想要的功能，但是我不太清楚.

How would I map this using NHibernate? I believe the component tag in the hbm file should do what I want, but I can't quite figure it out.

我的域是否因为我的证书类具有DateAcquired属性而无法使用?日期确实只是拥有证书的人的问题.

Is my domain out of whack because I have a DateAcquired property on my Certificate class? The date really is only a concern of a Person that has a certificate.

我现在已经更改了域模型，以反映需要一个新实体.现在，对于映射，我需要3个(对于每个实体)映射，还是可以对2个(对于Person和Certificate)进行映射?

I've altered the domain model now to reflect that a new entity is needed. Now for the mapping do I need 3 (for each entity) mappings or can I do it with 2 (for Person and Certificate)?

推荐答案

通过设计，如果除了中间(中间)表中表示的那对FK之外绝对没有其他内容，NHibernate仅支持隐式多对多映射拥有多对多关系.

By design, NHibernate only supports the implicit many-to-many mapping if there is absolutely NOTHING other than the pair of FKs represented in the intermediate (middle) table that holds the many-to-many relationship.

前段时间，Billy McCafferty在博客上写了这个确切的问题"(自从其BY DESIGN以来就不是一个真正的问题)...

Some time ago, Billy McCafferty blogged about this exact 'issue' (not really an issue since its BY DESIGN)...

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