NHibernate QueryOver - collection with too many results

Question

Dear NHibernate users,

I've been trying, reading and whatnot for 2 days now, but still can't figure this out, even though I presumed it to be an easy task with QueryOver API.

These are my two entities:

ATTRIBUTE
---------------------------
public int Id { get; set; }
public int LanguageId { get; set; }
public string Title { get; set; }
public IList<Option> Options { get; set; }


OPTION
---------------------------
public int Id { get; set; }
public Attribute Attribute { get; set; }
public int LanguageId { get; set; }
public string Title { get; set; }

The mapping is as follows:

<class name="Attribute" lazy="false" table="attribute" dynamic-insert="true" dynamic-update="true" select-before-update="true">
    <id name="Id" column="attribute_id" type="System.Int32">
        <generator class="native"/>
    </id>

    <bag name="Options" lazy="false" cascade="all">
        <key column="attribute_id" not-null="true" />
        <one-to-many class="Option" not-found="ignore" />
    </bag>

    <join table="attribute_i18n" inverse="true" fetch="join">
        <key column="attribute_id" not-null="true"/>
        <property name="LanguageId" column="language_id" type="System.Int32" not-null="true" />
        <property name="Title" column="title" type="System.String" length="255" not-null="true" />
    </join>
</class>

<class name="Option" lazy="false" table="options" dynamic-insert="true" dynamic-update="true" select-before-update="true">
    <id name="Id" column="option_id" type="System.Int32">
        <generator class="native"/>
    </id>

    <many-to-one name="Attribute" class="Attribute" column="attribute_id" not-null="true" />

    <join table="option_i18n" inverse="true" fetch="join">
        <key column="option_id" not-null="true"/>
        <property name="LanguageId" column="language_id" type="System.Int32" not-null="true" />
        <property name="Title" column="title" type="System.String" length="255" not-null="true" />
    </join>
</class>

Note that both tables join towards its own "i18n"-table (support of multilingual entries), and refer to its language_id column.

Furthermore, I try to use the QueryOver API, and query the Options-property for those options with LanguageId set to 1.

After a lot of hair pulling, my query is back to what I started with:

Attribute attribute = null;
Option option = null;

result = Session.QueryOver(() => attribute)
                .Where(() => attribute.LanguageId == 1)
                .Left.JoinAlias(i => i.Options, () => option)
                .Where(() => option.LanguageId == 1)
                .TransformUsing(Transformers.DistinctRootEntity)
                .List();

So, to my problem: This query keeps on giving me a double set of options in my option list (for language_id 1 and 2). I want to select only language_id = 1, but to my frustration the API doesn't understand me (..or was it the other way around?).

Any help on how to make my query work against my bag-collection of OPTIONs is greatly appreciated! :-) Thanks!

Mikal

Answer 1

I am afraid, that his won't work. By design and the nature of the <join>. As stated in the documentation:

5.1.19. join

Using the <join> element, it is possible to map properties of one class to several tables, when there's a 1-to-1 relationship between the tables.

The way how to (I do) solve this issue is a bit different. I have an object Language, the Option has colleciton of languages

public virtual IList<Language> Languages {get; set;}

The mapping is for example <bag>

<bag name="Languages"  batch-size="25"
  cascade="all-delete-orphan" inverse="true" >
  <key column="option_id" />
  <one-to-many class="Language" />

  <filter name="LanguagFilter" condition=":languageId = LanguageId" />
</bag>

The trick is in the filter. This is a dynamic version of the where mapping-attribute (18.1. NHibernate filters)

<filter-def name="LanguageFilter" >
  <filter-param name="languageId" type="Int32" />
</filter-def>

Then, we can turn the filter on, for all operations of the current session. Only once per request (if web app), inside some AOP, where we know the language id:

var filter = session.EnableFilter("LanguageFilter");
filter.SetParameter("languageId", theCurrentLanguageIdFromUser);

And finally, we know, that the collection Languages contains only one record and we can always access .First(). No more multiple results with more languages

Also see: https://stackoverflow.com/a/16625867/1679310, https://stackoverflow.com/a/18479266/1679310