HasMany().Not.KeyNullable() uni-directional mapping generates NULLable FK DDL

[ghost]

Hello,

It seems like HasMany().Not.KeyNullable() not quite properly generates DDL with SchemaExport. Assuming it should output NOT NULL FK column on the child side. However what I get is NULLable FK column.

HasMany(x => x.Items)
    .Not.Inverse()
    .Not.KeyNullable()
    .Not.KeyUpdate()
    .Cascade.AllDeleteOrphan();

The background of such modelling is the DDD related motivations where the AggregateRoot is managing its child entities, but children are not holding back reference to the AggregateRoot.

Am I doing something wrong or is this not working as I expect it to?

Cheers

[oleh-zheleznyak]

I have exactly the same need, and exactly the same problem.
In my project, we also have an AggregateRoot that is managing a collection of child entities, also using composition, so deleting orphans is also a must.

It is not a problem to alter the database script by hand, since we do not rely on automatic schema updates, and instead roll out hand-written migration scripts.

However, it would be nice to see that HNIbernate respects the mapping configuration, and generates proper schema. Otherwise, how can we be sure that it won't try to do insert null and then subsequent update to a value during session flush at runtime?

[rgomez90]

What's the state of this?

[hazzik]

@rgomez90 as far as I know, no one work on this. You are more than welcome to submit a PR. See contributing.

[rgomez90]

@hazzik thank you.
Will take a look at it in the weekend.

[TraGicCode]

@rgomez90 ,

Did u attempt to fix this bug yet or did you blocked?

[TraGicCode]

Hey,

looking at the generated mapping xml fluent nhibernate generated i see this

<bag access="nosetter.camelcase" cascade="all-delete-orphan" name="XXX">
      <key not-null="true" update="false">
        <column name="LineItem_id" />
      </key>
      <one-to-many class="XXX.Domain.XXX, XXX.Domain, Version=67.2017.9.1, Culture=neutral, PublicKeyToken=null" />
    </bag>

In the documentation here ( https://nhibernate.info/doc/nhibernate-reference/collections.html#collections-example) it show what the xml mapping should look like if you want the FK to be not nullable

 <set name="Children">
            <key column="parent_id" not-null="true"/>
            <one-to-many class="Child"/>
        </set>

Notice the different in the column attribute vs the column node. Are the both the same and valid mappings?

[hazzik]

Notice the different in the column attribute vs the column node. Are the both the same and valid mappings?

yes

[oskarb]

Also seeing this. It seems at least the schema generator is not picking up the not-null value from the parent key element when the column is a child, not an attribute.

[oskarb]

In NHibernate, the column name as a child element versus as an attribute produces different while the HbmXxx XML schema classes are interpreted into the Table mapping objects.

CollectionBinder.BindKey() will get the HbmKey object, then call ValuePropertyBinder.BindSimpleValue(). The third parameter of that method is called isNullable and it gets the value model.IsOneToMany (i.e. true). This becomes the default nullability for the columns.

Inside of that, it will iterate the columns (as HbmColumn). If the not-null attribute as been specified on the column element, it is respected. Otherwise the default is used (which comes from the expression model.IsOneToMany).

None of the above directly looks at the not-null attribute on the key element. The only time where that seems to be used is when the column element has not been used. In that case, when getting the list of columns from HbmKey, it will generate a "fake" HbmColumn instance based on the attributes found directly on the key element.

So, in summary, the following two alternatives are not treated exactly the same by NHibernate:

<set name="Children">
    <key column="parent_id" not-null="true"/>
    <one-to-many class="Child"/>
</set>

<set name="Children">
    <key not-null="true">
        <column name="parent_id"/>
    </key>
    <one-to-many class="Child"/>
</set>

[oskarb]

There is a workaround:

HasMany(sg => sg.Items).AsSet()
                       .Not.KeyNullable()
                       .KeyColumns.Add("parent_id", part => part.Not.Nullable())

That works, as opposed to using the .KeyColumn("...") shorthand. The .Not.KeyNullable() is still required to make NHibernate treat the column correctly for inserts.