asked on
Oracle Data Reader Has One Row But I Can NOT Retrieve it.
Here is a code snippets and debug result:
**************************
sql = "SELECT O.Latitude L, O.Longitude M, D.Latitude, D.Longitude";
sql += " FROM Locations O, Locations D";
sql += " WHERE O.Town='" + OriginationComboBox.Text + "' AND";
sql += " D.Town='" + DestinationComboBox.Text + "'";
cmd = new OracleCommand(sql, con);
dr = cmd.ExecuteReader();
string x= dr[0]; //InvalidOperationExceptio
string y=dr.GetString(1); //InvalidOperationExceptio
**************************
Debug Result Using Immediate windows:
dr.HasRows
true
dr.HasRows
true
dr.Depth
0
dr.FieldCount
4
dr.GetName(0)
"L"
dr.Read()
true
dr.Read()
false
**************************
The attached picture shows a quick watch for dr (OracleDataReader) state at run time exactly when the InvalidOperationException was thrown.
**************************
If I excute the query utilizing SQLPlus IDE the result will be:
SQL> SELECT O.Latitude L, O.Longitude M, D.Latitude, D.Longitude
2 FROM Locations O, Locations D
3 WHERE O.Town='Amman' AND D.Town='Paris';
L M LATITUDE LONGITUDE
---------- ---------- ---------- ----------
31.57 35.52 48.5 2.2
SQL>
Capture.JPG
**************************
sql = "SELECT O.Latitude L, O.Longitude M, D.Latitude, D.Longitude";
sql += " FROM Locations O, Locations D";
sql += " WHERE O.Town='" + OriginationComboBox.Text + "' AND";
sql += " D.Town='" + DestinationComboBox.Text + "'";
cmd = new OracleCommand(sql, con);
dr = cmd.ExecuteReader();
string x= dr[0]; //InvalidOperationExceptio
string y=dr.GetString(1); //InvalidOperationExceptio
**************************
Debug Result Using Immediate windows:
dr.HasRows
true
dr.HasRows
true
dr.Depth
0
dr.FieldCount
4
dr.GetName(0)
"L"
dr.Read()
true
dr.Read()
false
**************************
The attached picture shows a quick watch for dr (OracleDataReader) state at run time exactly when the InvalidOperationException was thrown.
**************************
If I excute the query utilizing SQLPlus IDE the result will be:
SQL> SELECT O.Latitude L, O.Longitude M, D.Latitude, D.Longitude
2 FROM Locations O, Locations D
3 WHERE O.Town='Amman' AND D.Town='Paris';
L M LATITUDE LONGITUDE
---------- ---------- ---------- ----------
31.57 35.52 48.5 2.2
SQL>
Capture.JPG
Oracle DatabaseC#SQL
Last Comment
Anurag Thakur
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for that, i don't have an answer other than its just the way that the datareader works.
you are using datareader
data reader is a connected mode and does not bring data from the database in the connected mode till the time you do a read
so you have to use the read()
if (dr.HasRows)
{
while (dr.Read())
{
//do operation here
}
}
this is the reason you have to do a read
data reader is a connected mode and does not bring data from the database in the connected mode till the time you do a read
so you have to use the read()
if (dr.HasRows)
{
while (dr.Read())
{
//do operation here
}
}
this is the reason you have to do a read
But why so ? why I sould used Read() ?