Usage of Repository Pattern

Question

I'm using the Repository pattern in my application right now. It is a console-based batch processing tool. Essentially I need the repository to be able to randomly access the data. The trouble I am having is that my data needs to be:

1. read in once (from flat-file)
2. accessed randomly from the repository
3. written out once.

I handle this in the code by using a guard clause to see if the records have been accessed yet, and if not then read them in. A simple example below.

public IUnit GetById(int id)
{
    if (!ReadIn)
    {
         ReadAllUnitsFromFile();
    }
    return _listOfUnits[id];
}

My question is this: Would it be a bastardization of the Repository pattern if I had a module that ran before the rest of my program to read the data into the repository, and another module that ran afterward to write data out of the repository? Is this an anti-pattern? Is there a better pattern to suit my situation?

Thanks

Answer 1

The whole point of the repository pattern is to allow you to abstract away the implementation behind a generic interface. You can use whatever method works best for your situation, and if you want to change it later, it shouldn't affect the rest of your application.

Use whatever implementation works best (and is the easiest to understand and maintain).

Answer 2

I would consider combining Unit of Work pattern with Repository pattern.

The unit of work is similar to a transaction (and often wraps one) and would be responsible for telling the repository to load data initially and save it at the end.

Answer 3

I think that the best code is what works (and is clean, testable, maintainable of course), regardless of whether it faithfully implements some pattern or not.

If you need to use most or all of the records during processing, to me it sounds perfectly fine to read all data eagerly before and save it after. Lazy loading always complicates the code, it may introduce concurrency problems etc. So it is only worth using if it can actually save execution time, when the data is often not needed at all, or needed only late in the process, or it can be loaded in little portions to improve startup time.

Moreover, AFAIK there is nothing in the Repository pattern mandating lazy loading of items - you are free to load them however it fits you behind the curtain. As for loading and saving items by a different external module, this may indeed break the encapsulation of the interface, but I believe it is possible to move those modules behind the repo interface as well - it can have init and shutdown methods.