Circular-dependency best practice

Question

I'm currently writing a web scraper which retrieves information from the internet. Simplified it looks like this.

Data access project

Objects to retrieve raw data
Objects to parse the the raw data into objects (!!)
The entities that the parser returns.

Now, I'm creating the actual parser, and I'm going to use it like this:

using Application.DataAccess;
using Application.DataAccess.Entities;

namespace Application{
 public class TestScraper{
  public static ScrapeIt()
  {
   var source = DataAcces.Retriever.Retrieve("http://example.com");
   DataAccess.Entities.Entity entity = DataAccess.Parser.Parse(source);

   //Do stuf with source here.
  }
 }
}

As you can see, the Parser returns a Entity. However this is in the DataAccess namespace, yet, it makes no sense... it´s a circle, and I don´t really know how to fix this. Well I could come up with a few things, like creating another layer between those layers.

But I just want to know, how would YOU solve this. And what is a good (or the best practice) for this.

Why are your retrievers and parses in the data access namespace, surely they have nothing to do with data access until you come to save the entity? — Hawxby, Jan 19 '11 at 12:14
@Beliskner I've tried to compare it with a SQL DAL. The functions that get the information from the SQL servers are usually in the DAL (comparable to my retrieves), and the functions that convert the raw data to usable objects are usually also in the DAL (comparable to my parser). — Timo Willemsen, Jan 19 '11 at 12:21

Ed Guiness · Accepted Answer · 2011-01-19T12:24:03.183

13

You can fix a circular reference by factoring out the things that both classes refer to into a new class, and then the old classes both refer to the new class.

So in your case you could move the entities out of DataAccess and into perhaps a new Entities namespace, used by both DataAccess and Application.

By doing this you start with

A <--> D

and end up with

A --> E
D --> E

edited Jan 19 '11 at 12:24

answered Jan 19 '11 at 12:15

Ed Guiness

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+1 - This is how I would do it. Define common dependencies that create the circular reference and then extract them out. – Joel Etherton Jan 19 '11 at 12:17
can you give an example of this. as i am confused whether the new class just include header declaration and it has its own class or just header declaration work? – Waqas Ahmed Oct 19 '16 at 11:40
@WaqasAhmed, E will contains abstraction/interfaces. – Jatin Dave Jun 13 '21 at 18:54

score 1 · Answer 2 · answered Jan 19 '11 at 12:19

Data Access Layer should not be in the same namespace as your domain objects. Entities should stand alone in an assembly/namespace that does not reference any other namespace, which will allow other logic based classes such as DataAccess and Parsers to reference the Entity on their own in a more clean manner.

Circular-dependency best practice

2 Answers2

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