Question

Just a quick question: In an OOP MVC application, one key principle is the seperation of responsibilities. I therefor think that a model and the object that fetches the model from a database, file, xml, webservice, etc. should be seperated from the model itself. This can for example be done by implementing a datamapper.

However, what do I do when I have a model that can be loaded from different sources? Should the model be in charge of the datasource, or is this the responsibility of the controller?

An simple example could be a config class that can be loaded from a database or a file. Should the controller instruct the datasource, or should the model know when to load the config info from a database or a file?

Answer 1

have used frameworks were the datasource is informed by the controller MachII, Model-Glue (Coldfusion frameworks) and also from the model layer (ColdSpring) – like Spring in Java.

I think the key thing is to use what makes more sense to you, keep the coupling to a minimum and be consistent, meaning don’t put datasource or object dependencies in multiple places.

You could also consider using a service type object to abstract the datasource and have it serve either who it likes.

That IOC file could look like this:

<?xml version="1.0" encoding="UTF-8"?>

<beans>

  <bean id="chartShareObj" class="model.charts.ChartShared" autowire="byType" />
  <bean id="trendChartObj" class="model.charts.TrendChart" autowire="byType" />

  <bean id="adminRightsDA0" class="org.datamentor.institution.RightsDAO">
    <constructor-arg name="dsn">
      <value>${dsn_dm}</value>
    </constructor-arg>
  </bean>

  <bean id="assessmentManager" class="model.assessment.Manager">
    <constructor-arg name="dsn">
      <value>${dsn_au}</value>
    </constructor-arg>
  </bean>

</beans>

You can see the different datasources specified by args via args defined in a controller.