Associated blog article: http://jason-mitchell.com/c/data-access-using-a-generic-repository-in-c/

Customer.cs

public class Customer
{
    [Key]
    public int ID { get; set; }
 
    [Required]
    public string FirstName { get; set; }
 
    [Required]
    public string LastName { get; set; }
}

EntityFrameworkRepository.cs

public class EntityFrameworkRepository : IRepository
{
    private readonly SiteDataContext dataContext;
 
    public EntityFrameworkRepository(SiteDataContext dataContext)
    {
        this.dataContext = dataContext;
    }
 
    public void Save()
    {
        dataContext.SaveChanges();
    }
 
    public IQueryable<T> Query<T>(Expression<Func<T, bool>> filter = null) where T : class
    {
        IQueryable<T> query = dataContext.Set<T>();
 
        if (filter != null)
            query = query.Where(filter);
 
        return query;
    }
 
    public T SingleOrDefault<T>(Expression<Func<T, bool>> predicate) where T : class
    {
        return dataContext.Set<T>().SingleOrDefault(predicate);
    }
 
    public void Insert<T>(T entity) where T : class
    {
        dataContext.Set<T>().Add(entity);
    }
 
    public void Update<T>(T entity) where T : class
    {
        DbEntityEntry entityEntry = dataContext.Entry(entity);
        if(entityEntry.State == EntityState.Detached)
        {
            dataContext.Set<T>().Attach(entity);
            entityEntry.State = EntityState.Modified;
        }
    }
 
    public void Delete<T>(T entity) where T : class
    {
        dataContext.Set<T>().Remove(entity);
    }
}

IRepository.cs

public interface IRepository
{
    void Save();
 
    IQueryable<T> Query<T>(Expression<Func<T, bool>> filter = null) where T : class;
    T SingleOrDefault<T>(Expression<Func<T, bool>> predicate) where T : class;
    void Insert<T>(T entity) where T : class;
    void Update<T>(T entity) where T : class;
    void Delete<T>(T entity) where T : class;
}

Sample.cs

var customers = from c in repository.Query<Customer>()
                where c.FirstName == "Jason"
                select c;

var customer = repository.Query<Customer>(c => c.FirstName == "Jason");