在Linq to SQL 中的helper

/// <summary>
    /// Linq通用数据访问类
    /// 指定TDataBase来代替后面要使用的数据上下文(指代)
    /// where：说明指代的类型
    /// new：限定必须有一个不带参数的构造函数
    /// </summary>
    /// <typeparam name="TDataBase"></typeparam>
    public class LinqHelper<TDataBase> where TDataBase : DataContext, new()
    {
        private readonly string connStr = "server=.;uid=sa;pwd=123456;database=StuDB";
        TDataBase db = null;
        /// <summary>
        /// 创建数据库连接
        /// </summary>
        public LinqHelper()
        {
            db = new TDataBase();
            db.Connection.ConnectionString = connStr;
        }

        /// <summary>
        /// 获取所有数据
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <returns></returns>
        public List<T> GetList<T>() where T : class
        {
            return db.GetTable<T>().ToList();
        }

        /// <summary>
        /// 按条件查询
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="predicate">Lambda表达式</param>
        /// <returns></returns>
        public List<T> GetList<T>(Expression<Func<T, bool>> predicate) where T : class
        {
            return db.GetTable<T>().Where(predicate).ToList();
        }

        /// <summary>
        /// 获取实体
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="predicate"></param>
        /// <returns></returns>
        public T GetEntity<T>(Expression<Func<T, bool>> predicate) where T : class
        {
            return db.GetTable<T>().Where(predicate).FirstOrDefault();
        }

        /// <summary>
        /// 添加实体
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="entity"></param>
        public void InsertEntity<T>(T entity) where T : class
        {
            try
            {
                //将对象保存到上下文当中
                db.GetTable<T>().InsertOnSubmit(entity);
                //提交更改
                db.SubmitChanges();
            }
            catch (Exception ex)
            {
                throw new Exception(ex.Message);
            }
        }

        /// <summary>
        /// 修改实体
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="entity"></param>
        public void UpdateEntity<T>(T entity) where T : class
        {
            try
            {
                //将新实体附加到上下文
                db.GetTable<T>().Attach(entity);
                //刷新数据库
                db.Refresh(RefreshMode.KeepCurrentValues, entity);
                //提交更改
                db.SubmitChanges(ConflictMode.ContinueOnConflict);
            }
            catch (Exception ex)
            {
                throw new Exception(ex.Message);
            }
        }

        /// <summary>
        /// 删除实体
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="predicate"></param>
        public void DeleteEntity<T>(Expression<Func<T, bool>> predicate) where T : class
        {
            try
            {
                //获取要删除的实体
                var entity = db.GetTable<T>().Where(predicate).FirstOrDefault();
                db.GetTable<T>().DeleteOnSubmit(entity);
                db.SubmitChanges(ConflictMode.ContinueOnConflict);
            }
            catch (Exception ex)
            {                
                throw new Exception(ex.Message);
            }
        }
    }