反射的应用
1．查找指定ID的数据
//查找指定id的数据，返回指定的对象
private T FindData<T>(int id)
{
Type ty = typeof(T);
//在这里创建实例对象的时候不能转成指定的类型，只能是Object对象
//转成指定类型后面就赋值不成功
// T t=(T)Activator.CreateInstance(ty);
//原来我是这么写的，也能创建实例对象，但后面怎么赋值都不行，全是NULL，
//特别要注意这点，要赋值完后才转成指定的类型
object obj = Activator.CreateInstance(ty);
string sql = $"select * from [{ty.Name}] where ID={id}";
OleDbConnection conn = new OleDbConnection(connString);
OleDbCommand cmd = new OleDbCommand(sql, conn);
conn.Open();
OleDbDataReader dr = cmd.ExecuteReader();
dr.Read();
foreach (var v in ty.GetFields())
{
if(v.FieldType.FullName=="System.Int32") //在这判断字段类型，我这只有两种类型int,string,如果类型多就要多写几种判断
{
obj.GetType().GetField($"{v.Name}").SetValue(obj, int.Parse(dr[$"{v.Name}"].ToString())); //第一种方法赋值
}
else
{
ty.GetField(name: $"{v.Name}").SetValue(obj, dr[$"{v.Name}"].ToString()); //第二种方法赋值
}
}
dr.Close();
conn.Close();
//var vname = obj.GetType().GetField("mAge");
//vname.SetValue(obj, 23);
//赋值完了才转成指定的类型
return (T)obj;
}
2．添加数据到数据库中
private bool Insert_Into<T>(T t)
{
int nRet = 0;
string intoSql = null;
string fileName = null;
string fileValue = null;
List<OleDbParameter> parList = new List<OleDbParameter>();
Type ty = t.GetType();
foreach (System.Reflection.FieldInfo v in ty.GetFields())
{
fileName += v.Name + ",";
fileValue += $"@{v.Name},";
OleDbParameter par = new OleDbParameter($"@{v.Name}", v.GetValue(t));
parList.Add(par);
}
fileName = fileName.Substring(0, fileName.Length - 1);
fileValue = fileValue.Substring(0, fileValue.Length - 1);
intoSql = $"INSERT INTO [{ty.Name}] ({fileName}) VALUES ({fileValue})";
using (OleDbConnection conn = new OleDbConnection(connString))
{
using (OleDbCommand cmd = new OleDbCommand(intoSql, conn))
{
cmd.Parameters.Clear();
cmd.Parameters.AddRange(parList.ToArray());
conn.Open();
nRet = cmd.ExecuteNonQuery();
conn.Close();
}
}
return nRet == 1;
}
3．修改数据
private bool UpdateData<T>(int id,T t)
{
int nRet = 0;
string intoSql = null;
string fileName = null;
List<OleDbParameter> parList = new List<OleDbParameter>();
Type ty = t.GetType();
foreach (System.Reflection.FieldInfo v in ty.GetFields())
{
fileName += v.Name + $"=@{v.Name},";
OleDbParameter par = new OleDbParameter($"@{v.Name}", v.GetValue(t));
parList.Add(par);
}
fileName = fileName.Substring(0, fileName.Length - 1);
intoSql = $"UPDATE [{ty.Name}] SET {fileName} WHERE ID={id}";
using (OleDbConnection conn = new OleDbConnection(connString))
{
using (OleDbCommand cmd = new OleDbCommand(intoSql, conn))
{
cmd.Parameters.Clear();
cmd.Parameters.AddRange(parList.ToArray());
conn.Open();
nRet = cmd.ExecuteNonQuery();
conn.Close();
}
}
return nRet == 1;
}
4．删除数据
private bool DeleteData<T>(int id)
{
int nRet = 0;
string intoSql = null;
Type ty = typeof(T);
intoSql = $"DELETE FROM [{ty.Name}] WHERE ID={id}";
using (OleDbConnection conn = new OleDbConnection(connString))
{
using (OleDbCommand cmd = new OleDbCommand(intoSql, conn))
{
conn.Open();
nRet = cmd.ExecuteNonQuery();
conn.Close();
}
}
return nRet == 1;
}
5．读取所有数据，返回一个所有数据的表
private DataTable GetDataTable<T>()
{
DataTable dt = new DataTable();
Type ty = typeof(T);
string sql = $"SELECT * FROM [{ty.Name}]";
using (OleDbConnection conn = new OleDbConnection(connString))
{
using (OleDbCommand cmd = new OleDbCommand(sql, conn))
{
conn.Open();
OleDbDataAdapter da = new OleDbDataAdapter(cmd);
da.Fill(dt);
}
conn.Close();
}
return dt;
}