DataReader怎样判断是否为空啊？

Question

OleDataReader reader;while (reader.Read())
{
  //...
}

Answer 1

DataReader dr = cmd.ExecuteReader();
if(dr.read()) //check whether the DataReader has got some values
{
  ...
}
dr.close();

Answer 2

SqlCommand thisCommand=thisConnection.CreateCommand();
thisCommand.CommandText="SELECT * FROM 班级";
SqlDataReader thisReader=thisCommand.ExecuteReader();
while(thisReader.Read())
{
if(thisReader["年级"].ToString().Trim()==comboBox1.Text.Trim() && thisReader["班级名称"].ToString().Trim()==textBox1.Text.Trim())
{
MessageBox.Show("该班已存在！");
i=0;
thisReader.Close();
thisConnection.Close();
break;
}
else
{
i=1;
}
} thisReader.Close(); if(i==1)
{
SqlDataAdapter thisAdapter=new SqlDataAdapter("SELECT * FROM 班级",thisConnection);
SqlCommandBuilder thisBuilder=new SqlCommandBuilder(thisAdapter); DataSet thisDataSet=new DataSet(); thisAdapter.Fill(thisDataSet,"班级"); DataRow thisRow=thisDataSet.Tables["班级"].NewRow();
thisRow["年级"]=comboBox1.Text.Trim();
thisRow["班级名称"]=textBox1.Text.Trim();
thisRow["人数"]="0";
thisRow["班主任"]=textBox2.Text.Trim();
thisRow["班主任手机"]=textBox3.Text.Trim();

thisDataSet.Tables["班级"].Rows.Add(thisRow); thisAdapter.Update(thisDataSet,"班级"); thisConnection.Close(); MessageBox.Show("修改成功！"); this.Close();

Answer 3

用IsNull方法。可以判断某个字段内容是否为空值

Answer 4

SqlCommand thisCommand=thisConnection.CreateCommand();
thisCommand.CommandText="SELECT * FROM 班级";
//把数据访问放到try ... catch ... 里，看看是否有异常抛出
try
{
SqlDataReader thisReader=thisCommand.ExecuteReader();
while(thisReader.Read())
{
if(thisReader["年级"].ToString().Trim()==comboBox1.Text.Trim() && thisReader["班级名称"].ToString().Trim()==textBox1.Text.Trim())
{
MessageBox.Show("该班已存在！");
i=0;
thisReader.Close();
thisConnection.Close();
break;
}
else
{
i=1;
}
} thisReader.Close(); if(i==1)
{
SqlDataAdapter thisAdapter=new SqlDataAdapter("SELECT * FROM 班级",thisConnection);
SqlCommandBuilder thisBuilder=new SqlCommandBuilder(thisAdapter); DataSet thisDataSet=new DataSet(); thisAdapter.Fill(thisDataSet,"班级"); DataRow thisRow=thisDataSet.Tables["班级"].NewRow();
thisRow["年级"]=comboBox1.Text.Trim();
thisRow["班级名称"]=textBox1.Text.Trim();
thisRow["人数"]="0";
thisRow["班主任"]=textBox2.Text.Trim();
thisRow["班主任手机"]=textBox3.Text.Trim();

thisDataSet.Tables["班级"].Rows.Add(thisRow); thisAdapter.Update(thisDataSet,"班级"); thisConnection.Close(); MessageBox.Show("修改成功！"); this.Close();
}
catch(Exception e)
{
  MessageBox.Show(e.Message);
}