Generic Repository with EntityFramework

Question

I'd like to implement a generic repository pattern using Entity Framework (I know there are many controversial opinions about repositories, but still this is what I need). The interface I'd like it to have is as follows:

public interface IRepository
{
    IQueryable<TEntity> Query<TEntity>() 
        where TEntity: Entity;

    void Save<TEntity>(TEntity entity) 
        where TEntity : Entity;

    void Delete<TEntity>(TEntity entity) 
        where TEntity : Entity;
}

Entity is a base class that just has an int ID property. And to use it like this:

        IRepository repository = ... // get repository (connects to DB)
        int userId = GetCurrentUserId();
        if (!repository.Query<User>().Any(u => u.Id == userId)) // performs SELECT query
        {    /*return error*/    }

        var newOrder = new Order { UserId = userId, Status = "New" }
        repository.Save(newOrder); // performs INSERT query
        ...
        newOrder.Status = "Completed";
        repository.Save(newOrder); // performs UPDATE query

I'd like to avoid UnitOwWork and just commit all object changes to the DB once Save() or Delete() is called. What I want to do looks really simple, but I haven't found any examples of how to do it using EntityFramework.The closest example I could find is this answer, but it uses UnitOwWork and repository-per-entity, which is more complicated than what I need to do.

Answer 1

1-Create One Interface

interface IMain<T> where T : class
    {
        List<T> GetAll();
        T GetById(int id);
        void Add(T entity);
        void Edit(T entity);
        void Del(int id);
        int Savechange();
    }

2-Create One Class

public class Main<T> : IMain<T> where T : class
    {
        public DataContext db;
        public void Add(T entity)
        {
            db.Set<T>().Add(entity);
        }

        public void Del(int id)
        {
            var q = GetById(id);
            db.Set<T>().Remove(q);
        }

        public void Edit(T entity)
        {
            db.Entry<T>(entity).State = EntityState.Modified;
        }

        public List<T> GetAll()
        {
            return db.Set<T>().Select(a=>a).ToList();
        }

        public T GetById(int id)
        {
            return db.Set<T>().Find(id);
        }

        public int Savechange()
        {
            return db.SaveChanges();
        }
    }

3-Create One Repository With Name YourTable ForExample Student

 public class Student : Main<Tbl_Student>
    {
        public Student()
        {
            db = new DataContext();
        }
    }

4-To Your Action Write This Code

Student student=new Student();
student.Del(3);
int a = student.Savechange();

Answer 2

You can do that with expression keyword;

    public interface IRepository<TEntity> where TEntity : Entity
    {
        IQueryable<TEntity> Query(Expression<Func<TEntity, bool>> predicate);

        void Save(TEntity entity);

        void Delete(TEntity entity);
    }

    public abstract class EfRepository<T> : IRepository<T> where T : Entity
    {
        private readonly DbContext _dbContext;
        protected readonly DbSet<T> _dbSet;
        public EfRepository(YourDbContextContext dbContext)
        {
            _dbContext = dbContext;
            _dbSet = dbContext.Set<T>();
        }

        public void Delete(T entity)
        {
            if (entity == null) return;
            else
            {
                DbEntityEntry dbEntityEntry = _dbContext.Entry(entity);

                if (dbEntityEntry.State != EntityState.Deleted)
                {
                    dbEntityEntry.State = EntityState.Deleted;
                }
                else
                {
                    _dbSet.Attach(entity);
                    _dbSet.Remove(entity);
                    _dbContext.SaveChanges();
                }
            }
        }

        public IQueryable<T> Query(Expression<Func<T, bool>> predicate)
        {
            return _dbSet.Where(predicate);
        }

        public void Save(T entity)
        {
            if (entity.Id > 0)
            {
                _dbSet.Attach(entity);
                _dbContext.Entry(entity).State = EntityState.Modified;
                _dbContext.SaveChanges();
            }
            else
            {
                _dbSet.Add(entity);
                _dbContext.SaveChanges();
            }
        }
    }
    public class Entity
    {
        public int Id { get; set; }
    }

Then create your repositories;

     public interface IUserRepository : IRepository<User>
     {
       //Also you can add here another methods according to your needs
     }
     public class UserRepository : EfRepository<User>,IUserRepository
     {
            public UserRepository(YourDbContext yourDbContext) : base(yourDbContext)
            {

            }
     }

Then use it;

IUserRepository _userRepository => Getit
//If there are entities according to your conditions, this will return them, then use it
_userRepository.Query(u => u.Id == userId);