C#自定义特性实例

Create Table Dept(  
    deptNo int identity(1,1) primary key,  
    dname nvarchar(10) not null,  
    description nvarchar(100)  
)  
Go  
-- 何问起 hovertree.com 

/**************自定义特性类*****************/  
/// <summary>  
/// 作用：用来说明表名是什么  
/// AttributeUsage:说明特性的目标元素是什么  
/// AttributeTargets.Class：代表目标元素为Class  
/// </summary>  
[AttributeUsage(AttributeTargets.Class)]  
public class TableAttribute : Attribute{  
  
    /// <summary>  
    /// 表名  
    /// </summary>  
    public string TableName { get; set; }  
 
    #region 构造方法，可选的  
  
    public TableAttribute() {    }  
    public TableAttribute(string tableName) {  
        this.TableName = tableName;  
    }   
 
    #endregion  
}  
  
/**************自定义特性类*****************/  
/// <summary>  
/// 作用：说明列是否为自动增长列  
/// </summary>  
[AttributeUsage(AttributeTargets.Property)]  
class IdentityAttribute: Attribute  
{  
    /// <summary>  
    /// true:是; false:否  
    /// </summary>  
    public bool IsIdentity { get; set; }  
}  
  
/****************实体类***************/  
/// <summary>  
/// 有意将类名定义成与表名不一致  
/// 用Table特性来说明实体类对应的表名是什么  
/// </summary>  
[Table(TableName = "Dept")]  
public class Department {  
  
    /// <summary>  
    /// 部门编号，用特性标注为自动增长  
    /// </summary>  
    [Identity(IsIdentity=true)]  
    public int DeptNo { get; set; }  
  
    /// <summary>  
    /// 部门名称  
    /// </summary>  
    public string Dname { get; set; }  
  
    /// <summary>  
    /// 部门描述  
    /// </summary>  
    public string Description { get; set; }  
  
    public Department( string name, string desc) {  
        Dname = name;  
        Description = desc;  
    }  
}  
  
/****************执行持久化操作类***************/  
/// <summary>  
/// 执行持久化操作类  
/// </summary>  
public class ADOManager {  
  
    /// <summary>  
    /// 将对象的属性值作为表中对应列的值来添加  
    /// </summary>  
    /// <param name="obj">要添加的对象</param>  
    public int Save(Object obj) {  
        //1.取得类名：代表表名,用到反射  
        string tableName = obj.GetType().Name;  
        //如果类有TableAttribute特性，在采用特性说明的类名  
        TableAttribute attr = Attribute.GetCustomAttribute(obj.GetType(), typeof(TableAttribute)) as TableAttribute;  
        if (attr != null) {//说明类加了Table特性  
            tableName = attr.TableName;//取得表名  
        }  
  
        //sql语句模板：insert into Dept(deptno,dname,description) values(‘2‘,‘‘,‘‘);  
        StringBuilder sql = new StringBuilder("insert into ");  
        sql.Append(tableName);  
        sql.Append(" (");  
  
        //循环对象的属性名：取得列名  
        foreach (PropertyInfo item in obj.GetType().GetProperties()) {  
            //取得是否有自动增长的特性  
            IdentityAttribute att = Attribute.GetCustomAttribute(item, typeof(IdentityAttribute)) as IdentityAttribute;  
            if (att == null || !att.IsIdentity) {//没有，则添加列  
                sql.Append(item.Name);  
                sql.Append(",");  
            }  
        }  
        //去除最后一个逗号‘  
        sql.Remove(sql.Length - 1, 1);  
        sql.Append(") values(");  
        //循环取出对象的属性值:为列赋值  
        foreach (PropertyInfo item in obj.GetType().GetProperties()) {  
            //取得是否有自动增长的特性  
            IdentityAttribute att = Attribute.GetCustomAttribute(item, typeof(IdentityAttribute)) as IdentityAttribute;  
            if (att == null) {//没有，则追加列的值  
                //GetValue():obj代表什么对象，null代表没有参数  
                sql.Append("‘" + item.GetValue(obj, null) + "‘");  
                sql.Append(",");  
            }  
        }  
  
        //去除最后一个逗号‘  
        sql.Remove(sql.Length - 1, 1);  
        sql.Append(")");  
        //查看完整的sql语句  
        Console.WriteLine(sql.ToString());  
  
        //执行sql语句  
        SqlConnection conn = new SqlConnection("server=.;database=test;integrated security=true");  
        SqlCommand comm = new SqlCommand(sql.ToString(), conn);  
        conn.Open();  
        int r = comm.ExecuteNonQuery();  
        conn.Close();  
  
        return r;//返回执行结果  
    }  
}  
  /* 何问起 hovertree.com */
/****************测试类关键代码***************/  
Department dept = new Department("开发部", "负责产品的研发");  
ADOManager manager = new ADOManager();  
int r = manager.Save(dept);  
  
Console.WriteLine(r==0?"失败":"成功");