今天有人问我Update语句怎么搞，想了一下大致思路就是用特性去标识一下，主键，然后再去用反射的方式拼sql语句。

想着晚上再写，又想了想的确好久没写博客了，也好久没正儿八经写代码了，就顺手给写了下来。

一、主键特性

/// <summary>
    /// 主键特性（在实体类的上方加这个特性，指定该类的主键名称）
    /// </summary>
    [AttributeUsage(AttributeTargets.Class)]
    public class PrimaryKeyAttribute : Attribute
    {
        private PrimaryKeyAttribute()
        {

        }

        private string _name;

        /// <summary>
        /// 构造方法
        /// </summary>
        /// <param name="name"></param>
        public PrimaryKeyAttribute(string name)
        {
            _name = name;
        }

        /// <summary>
        /// 主键名称
        /// </summary>
        public string Name
        {
            get { return _name; }
        }
    }

把这个特性加到实体类的上方，并指定主键名称，就可以了，示例：

image.png

二、拼写SQL语句

public class SqlBuilderHelper
    {
        /// <summary>
        /// 获得主键名称
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <returns></returns>
        private static string GetPK<T>() where T : class
        {
            string pkName = string.Empty;
            Type objTye = typeof(T);
            PrimaryKeyAttribute pk;
            foreach (Attribute attr in objTye.GetCustomAttributes(true))
            {
                pk = attr as PrimaryKeyAttribute;
                if (pk != null)
                    return pk.Name;
            }
            return pkName;
        }

        /// <summary>
        /// sql修改语句
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="entity"></param>
        /// <param name="tableName"></param>
        /// <returns></returns>
        public static string UpdateSql<T>(T entity, string tableName) where T : class
        {
            if (entity == null || string.IsNullOrEmpty(tableName))
            {
                return string.Empty;
            }

            string pkName = GetPK<T>();

            if (string.IsNullOrEmpty(pkName))
            {
                return string.Empty;
            }

            string pkValue = string.Empty;

            StringBuilder sb = new StringBuilder();
            sb.Append("update ");
            sb.Append(tableName);
            sb.Append(" set ");
            Type type = entity.GetType();
            PropertyInfo[] props = type.GetProperties();
            List<string> paraList = new List<string>();
            foreach (var prop in props)
            {
                if (prop.Name == (string)pkName)
                {
                    pkValue = (string)prop.GetValue(entity);
                }
                else
                {
                    paraList.Add(GetUpdatePara(prop, entity));
                }
            }

            if (paraList.Count == 0)
            {
                return string.Empty;
            }

            sb.Append(string.Join(",", paraList));

            if (string.IsNullOrEmpty(pkValue))
            {
                throw new Exception("主键不能为空");
            }

            sb.Append(" where ");
            sb.Append(pkName);
            sb.Append(" = ");
            sb.AppendFormat("'{0}'", pkValue);

            return sb.ToString();
        }

        /// <summary>
        /// 获得修改参数
        /// </summary>
        /// <param name="property"></param>
        /// <returns></returns>
        private static string GetUpdatePara<T>(PropertyInfo property, T entity)
        {
            StringBuilder sb = new StringBuilder();
            sb.AppendFormat(" {0}='{1}' ", property.Name, property.GetValue(entity));
            return sb.ToString();
        }
    }