Repository Pattern — Deep Dive with Generic Repository

Introduction

Article 19 introduced Repository + Unit of Work — this deep dive adds Specification pattern, read-only repos, async throughout, and honest guidance on when EF Core makes generic repos unnecessary.

After this article you will

• Implement IRepository<T> with specifications
• Build read-only query repositories
• Coordinate with Unit of Work
• Compare EF vs Dapper repository implementations
• Know when NOT to use repository over DbContext

Prerequisites

• Article 45 — CQRS with MediatR
• ShopNest API, EF Core, and DI from prior modules

Concept deep-dive

public interface ISpecification<T>
{
    Expression<Func<T, bool>>? Criteria { get; }
    List<Expression<Func<T, object>>> Includes { get; }
}

public class CustomerByRegionSpec : Specification<Customer>
{
    public CustomerByRegionSpec(string region) =>
        AddCriteria(c => c.Region == region);
}

public async Task<IReadOnlyList<Customer>> ListAsync(ISpecification<Customer> spec)
{
    return await ApplySpecification(_db.Customers, spec).ToListAsync();
}

When NOT to use: Simple apps where DbContext + specifications or direct LINQ is enough — avoid IRepository<T> that only wraps DbSet with no added value.

Hands-on — ShopNest CRM System

1. ICustomerRepository with GetById, List(spec), Add.
2. CustomerByRegionSpec + active-only spec.
3. UnitOfWork.SaveChangesAsync in CRM lead conversion flow.
4. Mock repository in CRM service unit test.

Common errors & best practices

• Leaking IQueryable from repository — callers compose unbounded queries.
• Generic repo returning IQueryable — prefer specifications or dedicated query methods.

Interview questions

Q: Specification pattern?
A: Encapsulates query logic reusable and testable without duplicating Where/Include chains.

Q: Repository over EF antipattern?
A: Debated — valuable for test seams and complex domains; redundant for trivial apps.

Summary

• Specifications encapsulate query intent for CRM
• Read-only repos prevent accidental writes on reports
• Unit of Work batches CRM transaction commits
• Use repositories when they add testability or abstraction

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