C#利用反射实现orm

之前用java做过一次，这次因为到公司用的是C#所以再做一次

主要用到的知识有：①特性（类似Java的注解）②反射③泛型④C#的数据库操作

特性

先定义一个特性，需要继承Attribute

using System;
using System.Data;

namespace SimpleORM.Attributes
{
    public class DataFieldAttribute: Attribute
    {
        public string _FieldName { get; private set; }
        public SqlDbType _FieldType { get; private set; }
        public int _Length { get; private set; }
        public DataFieldAttribute(string fieldname, SqlDbType fieldtype,int len)
        {
            _FieldName = fieldname;
            _FieldType = fieldtype;
            _Length = len;
        }
    }
}

然后就是使用它

using System.Data;

namespace SimpleORM.Attributes
{
    public class Bean
    {
        [DataField("ID",SqlDbType.Int,1)]
        public short id { get; private set; }

        [DataField("Name", SqlDbType.NVarChar,50)]
        public string name { get; private set; }

        [DataField("InDate", SqlDbType.DateTime,20)]
        public string InDate { get; private set; }

        [DataField("InUser", SqlDbType.NVarChar,15)]
        public string InUser { get; private set; }

        [DataField("LastEditDate", SqlDbType.DateTime, 20)]
        public string LastEditDate { get; private set; }


        [DataField("LastEditUser", SqlDbType.NVarChar,15)]
        public string LastEditUser { get; private set; }

        public Bean() { }

        public Bean(short id, string name, string InDate, string InUser, string LastEditDate, string LastEditUser)
        {
            this.id = id;
            this.name = name;
            this.InDate = InDate;
            this.InUser = InUser;
            this.LastEditDate = LastEditDate;
            this.LastEditUser = LastEditUser;
        }
    }
}

DateField是DataFieldAttribute的缩写，所以使用[DataFieldAttribute("ID",SqlDbType.Int,1)]也是可以的

反射

C#里的Type相当于java的Class，有两种方式可以获得Type对象：

①Type t=entity.getType();

②Type t=typeof(Entity);

利用反射操作属性

Bean entity=new Bean(.....);
PropertyInfo[] infos = entity.GetType().GetProperties();
foreach (PropertyInfo info in infos)
{
    //访问字段
    Console.WriteLine("字段名：{0},字段值{1}",info.Name,info.GetValue(entity));

    //访问特性
    Object[] dataFieldAttribute = info.GetCustomAttributes(typeof(DataFieldAttribute), false);
    DataFieldAttribute attr = dataFieldAttribute[0] as DataFieldAttribute;//强制转换
    Console.WriteLine("该字段的DataFieldAttribute特性：_FieldName--{0},_FieldType--{1},_Length--{2}",attr._FieldName,attr._FieldType, attr._Length);

    //设置字段值,需要注意的是利用反射设置值要保证类型相同
    info.SetValue(entity, Convert.ChangeType(这儿些你要转换的类型, info.PropertyType));
}

C#的数据库操作

用到的类有：

①SqlConnection       连接对象

②SqlCommand         组装sql语句，并且执行

③SqlParameter        预编译用

④SqlDataReader      返回的结果

string str="Server=...;UID=...;Password=...;Database=...";
SqlConnection conn=SqlConnection(str);
conn.Open();
SqlCommand cmd