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[英]SqlSessionState: Unable to cast object of type System.DBNull to type System.Byte[]
[英]Unable to cast object of type 'System.DBNull' to type 'System.Byte[]' when record does exist
我試圖從 MYSQL 讀取和下載 BLOB。 即使記錄存在,但我仍然不斷收到此錯誤。 以下是我的代碼:
this.Time = String.Format("{0:HH:mm:ss}", DropDownList1.SelectedValue);
String query = "Select * from event where time='" + this.Time + "'";
MySqlConnection conn = new MySqlConnection(connection);
MySqlCommand cmd = new MySqlCommand(query, conn);
String time = String.Format("{0:t}", DateTime.Today);
conn.Open();
MySqlDataReader r = cmd.ExecuteReader();
while (r.Read())
{
TextBox1.Text = r["name"].ToString();
TextBox2.Text = r["Proposedby"].ToString();
bytes = (byte[])r["proposalDoc"];
TextBox5.Text = Calendar1.SelectedDate.ToString("d");
TextBox6.Text = r["time"].ToString();
TextBox7.Text = r["Society"].ToString();
TextBox8.Text = r["venue"].ToString();
}
請告訴我如何消除這個錯誤。
可能是該記錄存在但錯誤告訴您proposalDoc
為db null。 所以靈魂將是檢查它是否是 db null 像這樣:
if(!Convert.IsDBNull(r["proposalDoc"]))
{
bytes = (byte[])r["proposalDoc"];
}
!string.IsNullOrEmpty(r["proposalDoc"].ToString())?(byte[])r["proposalDoc"] : null
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