SQLite数据库在执行更改表查询时被锁定C＃

Question

The following function is used for the newer version of my app which needs to add a column to the existing database.

public void AddColumnIfNotexist()
    {
      try
      {
       using (SQLiteCommand cmd = _DBConnection.CreateCommand())
       {
         cmd.CommandText = string.Format("SELECT sql FROM sqlite_master WHERE type = 'table' AND name = 'myTable'");
         bool hascol = false;
         using (SQLiteDataReader reader = cmd.ExecuteReader())
         {

           if (reader.Read())
           {
             //does column exists?
              hascol = reader.GetString(0).Contains(String.Format("\"{0}\"", "myNewColumn"));
             reader.Close();

            }
         }
               if (!hascol)
               {
                 StringBuilder sql = new StringBuilder(SQLMAXLENGTH);
                 sql.Append("ALTER TABLE Groups ADD COLUMN IsStayingRatio BIT NOT NULL DEFAULT 0");
                  cmd.CommandText = sql.ToString();
                  cmd.ExecuteNonQuery();


                  }
                    }
                }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message + "\r\n\r\n" + ex.StackTrace);
                LogApp.Write("Exception ex:" + ex.Message +"stacktrace "+ex.StackTrace, LogApp.Level.Error);

            }

        }
    }

When I execute this gets an exception as

database is locked

Stacktrace

at System.Data.SQLite.SQLite3.Step(SQLiteStatement stmt)
at System.Data.SQLite.SQLiteDataReader.NextResult()
at System.Data.SQLite.SQLiteDataReader..ctor(SQLiteCommand cmd, CommandBehavior behave)
at System.Data.SQLite.SQLiteCommand.ExecuteReader(CommandBehavior behavior)
at System.Data.SQLite.SQLiteCommand.ExecuteNonQuery(CommandBehavior behavior)
at System.Data.SQLite.SQLiteCommand.ExecuteNonQuery()
at DataPlus.DB.AddColumnIfNotexist() in D:\Projects\DB.cs:line 343

But this is not always happened. this happens if the size of the DB Fil is large. Also, the issue is not there while debugging from the IDE.

Is there any limitations for the Alter Table query? Can anyone spot out the issue which makes the DB locked?

Answer 1

I would suggest to start a new SQLiteCommand

Note that an SQLITE_LOCKED error is distinct from SQLITE_BUSY (5). SQLITE_BUSY means that another database connection (probably in another process) is using the database in a way that prevents you from using it. SQLITE_LOCKED means the source of contention is internal and comes from the same database connection that received the SQLITE_LOCKED error.

Sometimes people think they have finished with a SELECT statement because sqlite3_step() has returned SQLITE_DONE. But the SELECT is not really complete until sqlite3_reset() or sqlite3_finalize() have been called

Error Code SQLITE_LOCKED (6): Database Is Locked

Answer 2

Adding the following lines after reader.Close() worked for me.

GC.Collect();
GC.WaitForPendingFinalizers();

It seems that the DB was not released on executing the ALTER query. Got the hint from here .