Parametric 'UPDATE' string running with no errors but not doing anything

问题

I've recently changed an Update SQL string from dynamic SQL string to parametric SQL string. Here's what I had before:

OleDbConnection conn = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + this.DBstring);
OleDbCommand comm = new OleDbCommand();
comm.CommandText = "UPDATE myTable SET MY_FIELD='" + myString + "' WHERE F_SERIAL = '"+mySerial+"'";
comm.CommandType = CommandType.Text;
comm.Connection = conn;
conn.Open();
comm.ExecuteNonQuery();
conn.Close();

and here is what I have now:

OleDbConnection conn = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + this.DBstring);
OleDbCommand comm = new OleDbCommand();
comm.CommandText = "UPDATE myTable SET MY_FIELD = @myString WHERE F_SERIAL = @mySerial";
comm.Parameters.Add("@mySerial",OleDbType.VarWChar).Value = mySerial;
comm.Parameters.Add("@myString",OleDbType.VarWChar).Value = myString;
comm.CommandType = CommandType.Text;
comm.Connection = conn;
conn.Open();
comm.ExecuteNonQuery();
conn.Close();

The parameters are correctly set, as from the immediate window (I only show the first one, but the second has the same structure):

>>> comm.Parameters[0];
{@myString}
    base {System.Data.Common.DbParameter}: {@myString}
    DbType: String
    Direction: Input
    IsNullable: false
    OleDbType: VarWChar
    ParameterName: "@myString"
    Precision: 0
    Scale: 0
    Size: 15
    SourceColumn: ""
    SourceColumnNullMapping: false
    SourceVersion: Current
    Value: "test ++ ìì''' "

However, while the first code snippet used to work before, the new one doesn't. No error is raised, the execution goes fine, but the value in the Database is not updated. Does anyone have an idea on what could be going wrong? Am I maybe forgetting to do something? Sorry for the dumb question, but I really have nothing more than this and cannot figure out what's wrong.

回答1:

I finally solved my problem, something very weird. I will add an answer here in case someone could find it helpful in the future.

Basically, the problem was the order in which the parameters were added to the Parameters collection of the OleDbCommand object.

In my code, I was doing this:

comm.CommandText = "UPDATE myTable SET MY_FIELD = @myString WHERE F_SERIAL = @mySerial"; //<-- defining the command text
comm.Parameters.Add("@mySerial",OleDbType.VarWChar).Value = mySerial; //<-- parameter "mySerial" before "myString"
comm.Parameters.Add("@myString",OleDbType.VarWChar).Value = myString; //<-- parameter "myString" after "mySerial"

However, I'm using myString before mySerial, so basically the resulting query was:

UPDATE myTable SET MY_FIELD = mySerial WHERE F_SERIAL = myString

This, I'd say, is a bit strange because what's the reason of using parameter's names such as @myString or @mySerial if then the code only depends on their positioning inside the Parameters collection?

But well, the problem is now solved, and apparently someone else had already faced the same issue here. As the question's asker correctly says, OleDb can recognize that you are using a parameter but not what parameter you're using (???), making so everything dependent only on the order on which they are stored in the list.

I apologise for the "useless" question, but I hope at least the answer might turn to be useful to someone that, like me, in the future might struggle debugging for hours an apparently correct code not executing properly just because of the parameters' order within its list.

来源：https://stackoverflow.com/questions/29062668/parametric-update-string-running-with-no-errors-but-not-doing-anything

标签

sql

ms-access

oledb