C#反射在数据库连接时的应用

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;

}