HasMany Not Null Foreign Key

Question

I have two classes (simplified for the example):

public class Data
{
    public int Id {get; set;}
    public string Value { get; set; }
}
public class DataContainer
{
    public int Id {get; set;}
    public IList<Data> DataPoints { get; set; }
}

Basically the DataContainer class has a collection of Data (and other properties not shown). The Data class does not know about DataContainer but it cannot exist outside of one. I use a HasMany relationship for this.

I map DataContainer like this:

Id(x => x.Id);
HasMany<Data>(x => x.DataPoints)
    .Not.KeyNullable()
    .Cascade.All();

And the generated SQL for Data looks like this:

create table [Data] (
   [Id] INT IDENTITY NOT NULL,
   [DataContainer] INT null,
   primary key ([Id])
)
alter table [Data] 
    add constraint FK173EC9226585807B 
    foreign key ([DataContainer]) 
    references [DataContainer]

The problem is that I don't want [DataContainer] INT null, instead I want it not allow nulls

[DataContainer] INT not null

I thought .Not.KeyNullable() would do this but it doesn't seem to work.

Thanks.

@Phil, sorry only just saw your comment... Using Fluent 1.1 and NHibernate 2.1.2. — row1
– row1, Commented Jan 5, 2011 at 5:26

Yhrn · Accepted Answer · 2011-01-19 17:05:52Z

2

I have the exact same mapping and the same result but looking at the hbm.xml generated by Fluent it looks like it does what it can here. The collection mapping looks something like this (note the "not-null" attribute on the "key" element):

<bag cascade="all" name="Items" mutable="true">
  <key foreign-key="FK_MyEntity2_MyEntity1" not-null="true">
    <column name="MyEntity1_Id" />
  </key>
  <one-to-many class="MyNs.MyEntity2, MyAssembly, Version=0.4.700.0, Culture=neutral, PublicKeyToken=null" />
</bag>

Therefore I think this is a NHibernate issue rather than a Fluent issue. The following is taken from chapter 6.4 in the latest NHibernate reference (3.0.0 but I'm pretty sure the same is true for 2.1.2)

Very Important Note: If the <key> column of a association is declared NOT NULL, NHibernate may cause constraint violations when it creates or updates the association. To prevent this problem, you must use a bidirectional association with the many valued end (the set or bag) marked as inverse="true". See the discussion of bidirectional associations later in this chapter.

So my guess is that NHibernate simply ignores the "not-null" attribute when generating the DDL for this mapping and that the solution is to make the association bidirectional as suggested above (definitely works but may not suit your scenario) or live with a NULL column.

answered Jan 19, 2011 at 17:05

Yhrn

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2 Comments

Val M Over a year ago

I'm having exactly the same issue and have tried resolving as suggested above (adding the bidirectional relationship and setting the container end to Inverse) but my foreign keys are still nullable. Could someone give more details on a solution?

Yhrn Over a year ago

As I wrote in my comment to your answer: use References().Not.Nullable().

Val M · Accepted Answer · 2011-04-20 11:17:36Z

0

I have the same mapping and have resolved it by making the relationship bidirectional (as suggested by Yhrn) and then enforced the foreign key constraint by adding the Constrained().ForeignKey() declaration to the mapping:

In the Data class:

 this.HasOne(x => x.DataContainer).Cascade.All().Constrained().ForeignKey();

The column in the generated SQL is still nullable but the foreign key has been added:

ALTER TABLE [dbo].[Data]  WITH CHECK ADD  CONSTRAINT [FK_DataToDataContainer] FOREIGN KEY([Id])
REFERENCES [dbo].[DataContainer] ([Id])
GO

ALTER TABLE [dbo].[Data] CHECK CONSTRAINT [FK_DataToDataContainer]
GO

edited Apr 20, 2011 at 11:17

answered Apr 20, 2011 at 9:14

Val M

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2 Comments

Yhrn Over a year ago

Hi, HasOne should not be used here. It is only meant for one-to-one relations and this is a one-to-many relation. Instead use References().Not.Nullable().

Yhrn Over a year ago

Actully, this mapping you have made will only support one Data per DataContainer. The primary key in the Data table is also the foreign key to the DataContainer table, i.e. its a strict one-to-zero/one relation with a shared primary key.

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