How can I implement Entity Framework Repository Design Pattern in my C# DAL library?

Question

I use EF in my project and I want to implement the repository design pattern, but I want to have one super class which will take care for the Insert / Update / Delete / SaveChanges methods in order to avoid code duplication.

For example, I have these two interfaces ICostTypeRepository and IEmailRepository:

public interface ICostTypeRepository : IDisposable
{
        CostType GetCostTypeById(int pId);
        CostType GetCostTypeByCode(string pCode);
        IEnumerable<CostType> GetCostTypes();

        void Insert(CostType pCostType);
        void Update(CostType pCostType);
        void Delete(CostType pCostType);
        void SaveChanges();
}

public interface IEmailRepository : IDisposable
{
    Email GetEmailByID(int pId);
    IEnumerable<Email> GetEmails();
    Email GetEmailByAdress(string pAddress);

    void Insert(Email pEmail);
    void Update(Email pEmail);
    void Delete(Email pEmail);
    void SaveChanges();
}

What is the best way of creating an interface (and its implementation in a class) let's call it IDbOperations which will contain the CRUD methods only?

Something like

public interface IDbOperations : IDisposable
{     
    void Insert(??);
    void Update(??);
    void Delete(??);
    void SaveChanges();
}

What parameters will these CRUD methods take?

learn.microsoft.com/en-us/aspnet/mvc/overview/older-versions/… — Oluwafemi
– Oluwafemi, Commented Sep 16, 2017 at 21:37
You'd most likely have to make it a generic interface - IDbOperations<T>, and T would be the type of class you're using, e.g. IDbOperations<Email> would then have methods like Insert(Email email) etc. — marc_s
– marc_s, Commented Sep 16, 2017 at 21:37
Why do you need the repository pattern? Entity Framework DbContextes are already a repository pattern abstraction of sorts. — Brian Ogden
– Brian Ogden, Commented Sep 16, 2017 at 23:37
DbContext already has Insert, Update Delete and SaveChanges for any entity, why do you think you need to add another abstraction on top of this? — Brian Ogden
– Brian Ogden, Commented Sep 16, 2017 at 23:40

Daniel Botero Correa · Accepted Answer · 2019-11-13 09:04:05Z

Vane,

What you need is the generic repository pattern. You have to code the basic operations in a base class and then make extend all the repository classes from it. Inside each new repository class you can create more specific methods.

This is an example of a Generic Repository interface

public interface IGenericRepository<T> where T : class {

IQueryable<T> GetAll();
IQueryable<T> FindBy(Expression<Func<T, bool>> predicate);
void Add(T entity);
void Delete(T entity);
void Edit(T entity);
void Save();
}

You can implement the generic repository like this:

public class GenericRepository<C, T> : 
IGenericRepository<T> where T : class where C : DbContext, new() {

private C _entities = new C();
public C Context {

    get { return _entities; }
    set { _entities = value; }
}

public virtual IQueryable<T> GetAll() {

    IQueryable<T> query = _entities.Set<T>();
    return query;
}

public IQueryable<T> FindBy(System.Linq.Expressions.Expression<Func<T, bool>> predicate) {

    IQueryable<T> query = _entities.Set<T>().Where(predicate);
    return query;
}

public virtual void Add(T entity) {
    _entities.Set<T>().Add(entity);
}

public virtual void Delete(T entity) {
    _entities.Set<T>().Remove(entity);
}

public virtual void Edit(T entity) {
    _entities.Entry(entity).State = System.Data.EntityState.Modified;
}

public virtual void Save() {
    _entities.SaveChanges();
}
}

Now that you have the GenericRepository class, make FooRepository extend it and add specific methods (if needed) like this:

public class FooRepository :
GenericRepository<FooBarEntities, Foo>, IFooRepository {

public Foo GetSingle(int fooId) {

    var query = GetAll().FirstOrDefault(x => x.FooId == fooId);
    return query;
}
}

You should read about Unit of work pattern. It makes a lot of sense with the repository pattern. Please read this article from Microsoft.

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