R – How to prevent NHibernate queries from returning subclasses

nhibernate

I'm using the NHibernate criteria API to load some entities from my database. My domain consists of an abstract class, Animal, which the concrete Cat class inherits from. Another concrete class, Tiger, inherits from Cat.

I need to load all Cats from the database, so I'm doing the following-

ICriteria criteria = session.CreateCriteria(typeof(Cat));
return criteria.List<Cat>();

What I'm finding is that both Cats and Tigers are returned by the query instead of just Cats. This makes sense, as a Tiger is a Cat. But in this particular case I only want Cats, and not the additional Tigers.

Does anyone know how I can achieve this?

Best Answer

This is actually a Feature. But i think you can do what you want by mixing "table per class hierarchy" with "table per subclass". Therefor you need a Discriminator Column on which you can perform the query on. This would look like the following:

<class name="Cat" table="Cat">
    <id name="Id" type="Int64" column="ID">
        <generator class="native"/>
    </id>
    <discriminator column="TYPE" type="string"/>

    <subclass name="Tiger" discriminator-value="TIGER">
        <join table="Tiger">
            <property name="..." column="..."/>
        </join>
    </subclass>
</class>

After this you should be able to query on the discriminator-column like this:

session.CreateCriteria<Cat>()
   .Add(Restrictions.IsNull("TYPE"))
   .List<Cat>();

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R – Is it possible to map multiple tables to a single domain model using NHibernate

Yes, there are a number of options you can use to do what you want. Ayende Rahien has a great demonstration of the options for table inheritance and the resulting table structures.

Using the class hierarchy that has an abstract BaseOrder as a parent to CompleteOrder and IncompleteOrder, the union case is:

<class name="CompleteOrder" table="CompleteOrders">
    <id name="Id">
        <generator class="identity"/>
    </id>
    <property name="Status"/>
</class>

<class name="IncompleteOrder" table="IncompleteOrders">
    <id name="Id">
        <generator class="identity"/>
    </id>
</class>

 <class name="BaseOrder" abstract="true" table="Orders">
    <id name="Id">
        <generator class="hilo"/>
    </id>

    <union-subclass table="CompleteOrders" name="CompleteOrder">
        <property name="Status"/>
    </union-subclass>

    <union-subclass table="IncompleteOrders" name="IncompleteOrder">
    </union-subclass>
</class>

which also has separate tables but doesn't use a union for the query.

Check out the article, it will probably help greatly.

edit:

There was a comment about not wanting to cast but it's now gone. I'm not sure if it was deleted or if it was a SO issue...

If BaseOrder.Status is a virtual property, you should be able to pass around a BaseOrder and not need to cast. You'll have to maintain the extra class hierarchy but you can still query them together and, for the most part, the rest of the application shouldn't need to know about the subclasses.

Good luck!

Java – webjar not loading in spring boot application

You're referencing files called webjars/core-js/client/shim.min.js, however, this is not the correct path to the file except when you're using webjars-locator which provides version agnostic paths according to their documentation:

<dependency>
    <groupId>org.webjars</groupId>
    <artifactId>webjars-locator</artifactId>
</dependency>

In the comments you mentioned that Spring boot adds this dependency by itself, but this is not true. Spring boot does have the dependency listed, but only in the <dependencyManagement> section, which is not the same as adding a dependency.

Spring Web MVC also lists it as a dependency, but as an optional dependency, which means you have to explicitly add it.

Best Answer

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