Entity.cs

public abstract class Entity
{
    public int Id { get; set; }
}

EntityFrameworkSession.cs

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Data.Entity.Migrations;
using System.Linq;
using System.Linq.Expressions;

public class EntityFrameworkSession : ISession
{
    private readonly DbContext context;

    public EntityFrameworkSession(DbContext context)
    {
        this.context = context;
    }

    public T Find<T>(params int[] keyValues) where T : Entity
    {
        return context.Set<T>().Find(keyValues);
    }

    public T SingleOrDefault<T>(Func<T, bool> predicate) where T : Entity
    {
        return context.Set<T>().SingleOrDefault(predicate);
    }

    public T FirstOrDefault<T>(Func<T, bool> predicate) where T : Entity
    {
        return context.Set<T>().FirstOrDefault(predicate);
    }

    public IQueryable<T> All<T>() where T : Entity
    {
        return context.Set<T>().AsQueryable();
    }

    public void Add<T>(T entity) where T : Entity
    {
        context.Set<T>().Add(entity);
    }

    public void AddOrUpdate<T>(params T[] entities) where T : Entity
    {
        context.Set<T>().AddOrUpdate(entities);
    }

    public void AddOrUpdate<T>(Expression<Func<T, object>> identifierExpression, params T[] entities) where T : Entity
    {
        context.Set<T>().AddOrUpdate(identifierExpression, entities);
    }

    public void LoadReference<T, TProperty>(T entity, Expression<Func<T, TProperty>> navigationProperty)
        where T : Entity
        where TProperty : class
    {
        context.Entry(entity).Reference(navigationProperty).Load();
    }

    public void LoadCollection<T, TElement>(T entity, Expression<Func<T, ICollection<TElement>>> navigationProperty)
        where T : Entity
        where TElement : class
    {
        context.Entry(entity).Collection(navigationProperty).Load();
    }

    public int Commit()
    {
        return context.SaveChanges();
    }

    public void Delete<T>(T entity) where T : Entity
    {
        context.Set<T>().Remove(entity);
    }
}

ISession.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;

public interface ISession
{
    T Find<T>(params int[] keyValues) where T : Entity;

    T SingleOrDefault<T>(Func<T, bool> predicate) where T : Entity;

    T FirstOrDefault<T>(Func<T, bool> predicate) where T : Entity;

    IQueryable<T> All<T>() where T : Entity;

    void Add<T>(T entity) where T : Entity;

    void AddOrUpdate<T>(params T[] entities) where T : Entity;

    void AddOrUpdate<T>(Expression<Func<T, object>> identifierExpression, params T[] entities) where T : Entity;

    void LoadReference<T, TProperty>(T entity, Expression<Func<T, TProperty>> navigationProperty)
        where T : Entity
        where TProperty : class;

    void LoadCollection<T, TElement>(T entity, Expression<Func<T, ICollection<TElement>>> navigationProperty)
        where T : Entity
        where TElement : class;

    int Commit();

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