OOP Design – Understanding Relationships Between Entity Classes

designframeworksobject-orientedorm

I have at first sight a simple issue but can't wrap my head around on how to solve. I have an abstract class Compound. A Compound is made up of Structures. Then there is also a Container which holds 1 Compound.

A "special" implementation of Compound has Versions. For that type of Compound I want the Container to hold the Versionof the Compound and not the Compound itself.

You could say "just create an interface Containable" and a Container holds 1 Containable. However that won't work. The reason is I'm creating a framework and the main part of that framework is to simplify storing and especially searching for special data type held by Structure objects. Hence to search for Containers which contain a Compound made up of a specific Structure requires that the "Path" from Containerto Structure is well defined (Number of relationships or joins).

I hope this was understandable. My question is how to design the classes and relationships to be able to do what I outlined.

EDIT:

Kind of translation issue. with version i did not mean in terms of "versioning" but more in terms of "different variety" but fundamentally the same. There is no active / inactive. All are active.

EDIT 2:

Also note that these classes are entity classes and hence complex inheritance and hierarchies can be problematic.

EDIT 3:

Just don't see how either pattern (Composite, decorator) can work. I tried but the problem is the "path traversal", eg. implementing it in the context of Spring-data and QueryDSL.

I've created Class diagramm with comments that might help to understand the issue. Batch = Version.

Class Diagramm

Best Answer

... to search for Containers which contain a Compound made up of a specific Structure requires that the "Path" from Container to Structure is well defined (Number of relationships or joins).

Not if you are asking the container if it has such a structure yes or no, then only the container needs to know the path. You can keep it an implementation detail in such a case.

Implement a container class for version-less compounds, and an implementation for version-ed compounds. You indirectly traverse the structures through delegation.

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Here my current solution I came up with after some research. But please also post your solutions.

I went with my suggestion in the above edit. However only the affected methods in the DAO require these additional parameters (in my case 2 java.lang.Class Objects). DAO and Service Classes remain generic.

The trick however is to add a Constructor to your Service Class which takes those 2 Class Object Parameters as arguments. Then in the Spring configuration you need to create a service bean per class in the hierarchy you want to use. Example:

<bean id="myService1"  autowire="byName"
      class="MyServiceImpl">
    <constructor-arg index="0">
        <ref bean="CompoundClass"/>
    </constructor-arg>
    <constructor-arg index="1">
        <ref bean="CompoundQueryClass"/>
    </constructor-arg>
</bean>

<bean id="myService2"  autowire="byName"
      class="MyServiceImpl">
    <constructor-arg index="0">
        <ref bean="CompoundClass2"/>
    </constructor-arg>
    <constructor-arg index="1">
        <ref bean="CompoundQueryClass2"/>
    </constructor-arg>
</bean>

where the referenced beans are Class objects created like this:

<bean id="CompoundClass" class="java.lang.Class" factory-method="forName">
    <constructor-arg value="full.qualified.class.name"/>
</bean>

While the affected methods are now a bit cluttered (many arguments) and passing around Class objects seems non-ideal to me (probably I'm wrong) a developer using the framework will not have to deal with the issue. He can create his extended entities and apply the correct configuration. I've created tests for his and the solution those seem to work as expected.

If CompoundClass2 extends CompoundClass (which uses @DiscriminatorColumn) and I call a query method from MyServiceImpl only CompoundClass2 objects are in the result even if a CompoundClass object would match the query too + the right type is returned. No casting needed.

Frameworks Software Updates – Should You Keep Updating Bootstrap in Your Web Application?

You can think about updating Bootstrap the same way you would think about any other dependency.

Does it introduce breaking changes?
What benefits do you get from upgrading?
Do the benefits outweigh the risk or time investment?

In the context of a CSS (and potentially JS, if you use the helper scripts) dependency, these questions can be thought of this way:

If the class names used in Bootstrap change or the styles are significantly different which would break the styling on your site, this is a breaking change.
You might get access to better modularized code, a shinier grid, etc.
Getting improved benefits depends strongly on how much custom work you've already laid on top of your previous Bootstrap installation. If you've done a lot of work that depends on overriding the expected styles, it might not be worth it.

Personally, I consider CSS boilerplates to be set in stone for a project once I've started. I'm never going to modify the actual Bootstrap code itself, and I'm generally targeting the styles I want to specifically override from Bootstrap. This means that if I upgrade Bootstrap, many things will probably break in subtle ways that are hard to track down - for me, it's not worth the hassle for minimal gain. I'd just save using a new version of Bootstrap for the next application or next page.

The only exceptions I might see to this are pulling in the newer grid or layout-related code, but again, it depends on how much bespoke work you've done to the old version of your CSS dependencies.

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