如何使C＃ExecuteReader引发异常而不是挂起

Question

I have an application open which has called performed a SELECT using "FOR UPDATE" - locking the row.

When a second application tries to access the same row the application hangs (untill it times out) on:

// Simplified code
var connection = new MySqlConnection(connectionString);
connection.Open();

var transaction = connection.BeginTransaction();

MySqlCommand command = new MySqlCommand(sqlQuery, connection, transaction);
MySqlDataReader dataReader = command.ExecuteReader(); // HANGS

According to the documentation it says under SqlException:

An exception occurred while executing the command against a locked row

This is what I would like - to get an exception immediately. I tried to change the command timeout, but this just gives a TimeoutException and nothing explaining that the accurate reason.

Answer 1

Have you tried using try and catch?

var connection = new MySqlConnection(connectionString);
try

{


connection.Open();

var transaction = connection.BeginTransaction();

MySqlCommand command = new MySqlCommand(sqlQuery, connection, transaction);
MySqlDataReader dataReader = command.ExecuteReader(); 
}
catch (Exception)
        {
            throw;
        }

Answer 2

SqlExceptionThe default timeout period for SQL connection is something like 15 or 30 seconds. When your code attempts to read the data it waits for an answer or timeout. One way of doing this (I'm not sure how practical it is though - only a beginner at SQL) is reducing the timeout period and attempting to reconnect, while refreshing the program:

connection.ConnectionTimeout = 1; //timeout in seconds
//initialize command, connection etc
bool commited;
while(!commited){
   try{
      MySqlDataReader dataReader = command.ExecuteReader(); 
      commited = true;
   }catch(SqlException e) {
      commited = false;
   }
   //code to force program update.
}

And if you really want the "locked row" message, you can do it after 15 (or whatever amount you choose) of 1 second timeouts.