Pattern for multiple datasources

Sounds like you need a Repository pattern, maybe backed by a Strategy which would choose between different implementations.

How'd you actually do it is exposing a generic interface with your basic CRUD operations and make an implementation for each data source while letting the strategy pattern to decide on the implementation. If you're using dependency injection this might get a little tricky if deciding on which data source you're using is not easily deducted from the beginning.

It seems like there are two parts to your question:

• Getting the data from multiple sources
• Transforming the data to the expected format

The task of getting the data from the sources would be handled by the repository. Part of fetching the data is transforming it to it's expected format. The question you have to answer is: "What is the expected class?".

If this data is only used as this final singular type, then each repository will return the single type. A call to MyRepository will internally call each of the Source Repositories.

public class MyRepository {
  ISourceRepository[] Sources;

  private getFromSources(); 
  public getData(); //uses getFromSources
}

Sometimes the data is useful in it's original form as well as the final type, if this is the case, the repositories should return separate types, which you can then transform to the new type with something like the visitor pattern:

public class MyDataFormatter {
  public MyData format(SourceOne data);
  public MyData format(SourceTwo data);
  public MyData format(SourceThree data);
}

public class MyDataRepository {
  public IRepository Repos;
  public function getData() {
    get data from each repo in it's original format
    call MyDataFormatter.format(data)
  }
}

adapted from this link