samples/snippets/standard/data/sqlite/DirtyReadSample/Program.cs - main - aprogrammer/dotnet-docs

samples/snippets/standard/data/sqlite/DirtyReadSample/Program.cs

62 строки2 KB

Genevieve Warren

SFI: More ROPC work (#42687)

24 сен 2024, 18:12

24 сен 2024, 18:12069fe34

using System;
using System.Data;
using Microsoft.Data.Sqlite;

namespace DirtyReadSample
{
    class Program
    {
        static void Main()
        {
            // The connections must use a shared cache
            const string connectionString = "...";

            var firstConnection = new SqliteConnection(connectionString);
            firstConnection.Open();

            var secondConnection = new SqliteConnection(connectionString);
            secondConnection.Open();

            var createCommand = firstConnection.CreateCommand();
            createCommand.CommandText =
            @"
                CREATE TABLE data (
                    value TEXT
                );

                INSERT INTO data
                VALUES ('clean');
            ";
            createCommand.ExecuteNonQuery();

            #region snippet_DirtyRead
            using (var firstTransaction = firstConnection.BeginTransaction())
            {
                var updateCommand = firstConnection.CreateCommand();
                updateCommand.CommandText =
                @"
                    UPDATE data
                    SET value = 'dirty'
                ";
                updateCommand.ExecuteNonQuery();

                // Without ReadUncommitted, the command will time out since the table is locked
                // while the transaction on the first connection is active
                using (secondConnection.BeginTransaction(IsolationLevel.ReadUncommitted))
                {
                    var queryCommand = secondConnection.CreateCommand();
                    queryCommand.CommandText =
                    @"
                        SELECT *
                        FROM data
                    ";
                    var value = (string)queryCommand.ExecuteScalar();
                    Console.WriteLine($"Value: {value}");
                }

                firstTransaction.Rollback();
            }
            #endregion
        }
    }
}