Applying Repository Pattern to ReportViewModels

Question

public interface IRepository<TEntity> 
{
    TEntity FindById(Guid id);
    void Add(TEntity entity);
    void Remove(TEntity entity);
}

This is a simple generic repository. If I have a Product entity, this repository can insert, update, and delete (using Entity Framework).

But I have report based types that I created.

For example:

• Products that grouped by salesmen.

• Number of orders sent by each shipper.

  public class OrdersWithShipper {
       public string ShipperName{get;set;}
       public string NumberOfOrder{get;set;}
  }
  

And so on.

So I should create complex queries to many tables that related. But query result object is not representing with repository TEntity entity type.

I have many report type like this. How can I solve this problem?

Answer 1

The direct problem of this question is:

So I should create complex queries to many tables that related. But query result object is not representing with repository TEntity entity type.

I would say you should not be using the repository pattern here as it breaks it. E.g a repository should be dealing with returning and managing the domain object it is designed for, in order to support domain behavior, not random query objects to support reporting behavior.

By not sticking to the same type you will almost certainly end up not knowing where to draw the line, e.g what query object goes with what repository etc... So you should just keep it simple.

Apply a different pattern to reporting (or querying) for example. Maybe create classes for your view models (View Model Builders?) that are directly dependent on IDbSet<T> for their querying logic.

Or, abstract further and have a query handler / query provider pattern (this would be my choice).

Look at the answer here:

Well designed query commands and/or specifications

I have used similar pattern to this with great success.

Answer 2

My technique in doing this is to wrap the Repository in a Service class that can accept the ViewModels. In other words, my Controllers are using the Service classes that I make and not the repositories directly. Also, I use the AutoMapper library to map

Example below:

public class OrderWithShipperProductService()
{
    public ProductRepository { get; set; }

    public OrderWithShipperProductService(ProductRepository repo)
    {
        this.ProductRepository = repo;
    }

    public void AddOrderWithShipperProduct(OrderWithShipperProduct model)
    {
        var entity = Mapper.Map<TEntity>(model);
        ProductRepository.Add(entity);
    }
}

You may need to learn Automapper here. But you may also map it yourself in the constructor if you want. Or you may also create your own mapping functions.