Pemrograman Asinkron
Topik ini membahas dukungan untuk pemrograman asinkron di Penyedia Data .NET Framework untuk SQL Server (SqlClient) termasuk peningkatan yang dibuat untuk mendukung fungsionalitas pemrograman asinkron yang diperkenalkan di .NET Framework 4.5.
Pemrograman Asinkron Lama
Sebelum .NET Framework 4.5, pemrograman asinkron dengan SqlClient dilakukan dengan metode berikut dan properti koneksi Asynchronous Processing=true:
Fungsionalitas ini tetap berada di SqlClient di .NET Framework 4.5.
Tip
Dimulai di .NET Framework 4.5, metode warisan ini tidak lagi diperlukan Asynchronous Processing=true dalam string koneksi.
Fitur Pemrograman Asinkron Ditambahkan di .NET Framework 4.5
Fitur pemrograman asinkron baru menyediakan teknik sederhana untuk membuat kode asinkron.
Untuk informasi selengkapnya tentang fitur pemrograman asinkron yang diperkenalkan di .NET Framework 4.5, lihat:
Pemrograman Asinkron dengan Asinkron dan Tunggu (Visual Basic)
Menggunakan metode asinkron baru SqlDataReader di .NET Framework 4.5 (Bagian 1)
Menggunakan metode asinkron baru SqlDataReader di .NET Framework 4.5 (Bagian 2)
Ketika antarmuka pengguna Anda tidak responsif atau server Anda tidak menskalakan, kemungkinan Anda memerlukan kode Anda untuk lebih asinkron. Menulis kode asinkron secara tradisional melibatkan pemasangan panggilan balik (juga disebut kelanjutan) untuk mengekspresikan logika yang terjadi setelah operasi asinkron selesai. Ini mempersulit struktur kode asinkron dibandingkan dengan kode sinkron.
Anda sekarang dapat memanggil metode asinkron tanpa menggunakan panggilan balik, dan tanpa membagi kode Anda di beberapa metode atau ekspresi lambda.
Pengubah async menetapkan bahwa suatu metode tidak sinkron. Saat memanggil metode async, tugas dikembalikan. Saat operator await diterapkan ke tugas, metode saat ini segera keluar. Ketika tugas selesai, eksekusi dilanjutkan dengan metode yang sama.
Peringatan
Panggilan asinkron tidak didukung jika aplikasi juga menggunakan kata kunci string koneksi Context Connection.
Memanggil metode async tidak mengalokasikan utas tambahan apa pun. Ini dapat menggunakan utas penyelesaian I/O yang ada secara singkat di akhir.
Metode berikut ditambahkan di .NET Framework 4.5 untuk mendukung pemrograman asinkron:
Anggota asinkron lainnya ditambahkan untuk mendukung Dukungan Streaming SqlClient.
Tip
Metode asinkron baru tidak diperlukan Asynchronous Processing=true dalam string koneksi.
Koneksi Sinkron ke Asinkron Terbuka
Anda dapat meningkatkan aplikasi yang ada untuk menggunakan fitur asinkron baru. Misalnya, asumsikan aplikasi memiliki algoritma koneksi sinkron dan memblokir utas UI setiap kali terhubung ke database dan, setelah terhubung, aplikasi memanggil prosedur tersimpan yang memberi sinyal kepada pengguna lain dari yang baru saja masuk.
using SqlConnection conn = new SqlConnection("…");
{
conn.Open();
using (SqlCommand cmd = new SqlCommand("StoredProcedure_Logon", conn))
{
cmd.ExecuteNonQuery();
}
}
Ketika dikonversi untuk menggunakan fungsionalitas asinkron baru, program akan terlihat seperti:
using System;
using System.Data.SqlClient;
using System.Threading.Tasks;
class A {
static async Task<int> Method(SqlConnection conn, SqlCommand cmd) {
await conn.OpenAsync();
await cmd.ExecuteNonQueryAsync();
return 1;
}
public static void Main() {
using (SqlConnection conn = new SqlConnection("Data Source=(local); Initial Catalog=NorthWind; Integrated Security=SSPI")) {
SqlCommand command = new SqlCommand("select top 2 * from orders", conn);
int result = A.Method(conn, command).Result;
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
Console.WriteLine(reader[0]);
}
}
}
Menambahkan Fitur Asinkron Baru di Aplikasi yang Ada (Mencampur Pola Lama dan Baru)
Dimungkinkan juga untuk menambahkan kemampuan asinkron baru (SqlConnection::OpenAsync) tanpa mengubah logika asinkron yang ada. Misalnya, jika aplikasi saat ini menggunakan:
AsyncCallback productList = new AsyncCallback(ProductList);
SqlConnection conn = new SqlConnection("…");
conn.Open();
SqlCommand cmd = new SqlCommand("SELECT * FROM [Current Product List]", conn);
IAsyncResult ia = cmd.BeginExecuteReader(productList, cmd);
Anda dapat mulai menggunakan pola asinkron baru tanpa mengubah algoritma yang ada secara substansial.
using System;
using System.Data.SqlClient;
using System.Threading.Tasks;
class A {
static void ProductList(IAsyncResult result) { }
public static void Main() {
// AsyncCallback productList = new AsyncCallback(ProductList);
// SqlConnection conn = new SqlConnection("Data Source=(local); Initial Catalog=NorthWind; Integrated Security=SSPI");
// conn.Open();
// SqlCommand cmd = new SqlCommand("select top 2 * from orders", conn);
// IAsyncResult ia = cmd.BeginExecuteReader(productList, cmd);
AsyncCallback productList = new AsyncCallback(ProductList);
SqlConnection conn = new SqlConnection("Data Source=(local); Initial Catalog=NorthWind; Integrated Security=SSPI");
conn.OpenAsync().ContinueWith((task) => {
SqlCommand cmd = new SqlCommand("select top 2 * from orders", conn);
IAsyncResult ia = cmd.BeginExecuteReader(productList, cmd);
}, TaskContinuationOptions.OnlyOnRanToCompletion);
}
}
Menggunakan Model Penyedia Dasar dan Fitur Asinkron Baru
Anda mungkin perlu membuat alat yang dapat terhubung ke database yang berbeda dan menjalankan kueri. Anda dapat menggunakan model penyedia dasar dan fitur asinkron baru.
Microsoft Distributed Transaction Controller (MSDTC) harus diaktifkan di server untuk menggunakan transaksi terdistribusi. Untuk informasi tentang cara mengaktifkan MSDTC, lihat Cara Mengaktifkan MSDTC di Server Web.
using System;
using System.Data.Common;
using System.Data.SqlClient;
using System.Threading.Tasks;
class A {
static async Task PerformDBOperationsUsingProviderModel(string connectionString, string providerName) {
DbProviderFactory factory = DbProviderFactories.GetFactory(providerName);
using (DbConnection connection = factory.CreateConnection()) {
connection.ConnectionString = connectionString;
await connection.OpenAsync();
DbCommand command = connection.CreateCommand();
command.CommandText = "SELECT * FROM AUTHORS";
using (DbDataReader reader = await command.ExecuteReaderAsync()) {
while (await reader.ReadAsync()) {
for (int i = 0; i < reader.FieldCount; i++) {
// Process each column as appropriate
object obj = await reader.GetFieldValueAsync<object>(i);
Console.WriteLine(obj);
}
}
}
}
}
public static void Main()
{
SqlConnectionStringBuilder builder = new SqlConnectionStringBuilder();
// replace these with your own values
builder.DataSource = "your_server";
builder.InitialCatalog = "pubs";
builder.IntegratedSecurity = true;
string provider = "System.Data.SqlClient";
Task task = PerformDBOperationsUsingProviderModel(builder.ConnectionString, provider);
task.Wait();
}
}
Menggunakan Transaksi SQL dan Fitur Asinkron Baru
using System;
using System.Data.SqlClient;
using System.Threading.Tasks;
class Program {
static void Main() {
string connectionString =
"Persist Security Info=False;Integrated Security=SSPI;database=Northwind;server=(local)";
Task task = ExecuteSqlTransaction(connectionString);
task.Wait();
}
static async Task ExecuteSqlTransaction(string connectionString) {
using (SqlConnection connection = new SqlConnection(connectionString)) {
await connection.OpenAsync();
SqlCommand command = connection.CreateCommand();
SqlTransaction transaction = null;
// Start a local transaction.
transaction = await Task.Run<SqlTransaction>(
() => connection.BeginTransaction("SampleTransaction")
);
// Must assign both transaction object and connection
// to Command object for a pending local transaction
command.Connection = connection;
command.Transaction = transaction;
try {
command.CommandText =
"Insert into Region (RegionID, RegionDescription) VALUES (555, 'Description')";
await command.ExecuteNonQueryAsync();
command.CommandText =
"Insert into Region (RegionID, RegionDescription) VALUES (556, 'Description')";
await command.ExecuteNonQueryAsync();
// Attempt to commit the transaction.
await Task.Run(() => transaction.Commit());
Console.WriteLine("Both records are written to database.");
}
catch (Exception ex) {
Console.WriteLine("Commit Exception Type: {0}", ex.GetType());
Console.WriteLine(" Message: {0}", ex.Message);
// Attempt to roll back the transaction.
try {
transaction.Rollback();
}
catch (Exception ex2) {
// This catch block will handle any errors that may have occurred
// on the server that would cause the rollback to fail, such as
// a closed connection.
Console.WriteLine("Rollback Exception Type: {0}", ex2.GetType());
Console.WriteLine(" Message: {0}", ex2.Message);
}
}
}
}
}
Menggunakan Transaksi SQL dan Fitur Asinkron Baru
Dalam aplikasi perusahaan, Anda mungkin perlu menambahkan transaksi terdistribusi dalam beberapa skenario, untuk mengaktifkan transaksi antara beberapa server database. Anda dapat menggunakan namespace layanan System.Transactions dan mendaftarkan transaksi terdistribusi, sebagai berikut:
using System;
using System.Data.SqlClient;
using System.Threading.Tasks;
using System.Transactions;
class Program {
public static void Main()
{
SqlConnectionStringBuilder builder = new SqlConnectionStringBuilder();
// replace these with your own values
builder.DataSource = "your_server";
builder.InitialCatalog = "your_data_source";
builder.IntegratedSecurity = true;
Task task = ExecuteDistributedTransaction(builder.ConnectionString, builder.ConnectionString);
task.Wait();
}
static async Task ExecuteDistributedTransaction(string connectionString1, string connectionString2) {
using (SqlConnection connection1 = new SqlConnection(connectionString1))
using (SqlConnection connection2 = new SqlConnection(connectionString2)) {
using (CommittableTransaction transaction = new CommittableTransaction()) {
await connection1.OpenAsync();
connection1.EnlistTransaction(transaction);
await connection2.OpenAsync();
connection2.EnlistTransaction(transaction);
try {
SqlCommand command1 = connection1.CreateCommand();
command1.CommandText = "Insert into RegionTable1 (RegionID, RegionDescription) VALUES (100, 'Description')";
await command1.ExecuteNonQueryAsync();
SqlCommand command2 = connection2.CreateCommand();
command2.CommandText = "Insert into RegionTable2 (RegionID, RegionDescription) VALUES (100, 'Description')";
await command2.ExecuteNonQueryAsync();
transaction.Commit();
}
catch (Exception ex) {
Console.WriteLine("Exception Type: {0}", ex.GetType());
Console.WriteLine(" Message: {0}", ex.Message);
try {
transaction.Rollback();
}
catch (Exception ex2) {
Console.WriteLine("Rollback Exception Type: {0}", ex2.GetType());
Console.WriteLine(" Message: {0}", ex2.Message);
}
}
}
}
}
}
Membatalkan Operasi Asinkron
Anda dapat membatalkan permintaan asinkron dengan menggunakan CancellationToken.
using System;
using System.Data.SqlClient;
using System.Threading;
using System.Threading.Tasks;
namespace Samples {
class CancellationSample {
public static void Main(string[] args) {
CancellationTokenSource source = new CancellationTokenSource();
source.CancelAfter(2000); // give up after 2 seconds
try {
Task result = CancellingAsynchronousOperations(source.Token);
result.Wait();
}
catch (AggregateException exception) {
if (exception.InnerException is SqlException) {
Console.WriteLine("Operation canceled");
}
else {
throw;
}
}
}
static async Task CancellingAsynchronousOperations(CancellationToken cancellationToken) {
using (SqlConnection connection = new SqlConnection("Server=(local);Integrated Security=true")) {
await connection.OpenAsync(cancellationToken);
SqlCommand command = new SqlCommand("WAITFOR DELAY '00:10:00'", connection);
await command.ExecuteNonQueryAsync(cancellationToken);
}
}
}
}
Operasi Asinkron dengan SqlBulkCopy
Kemampuan asinkron juga ditambahkan ke System.Data.SqlClient.SqlBulkCopy dengan SqlBulkCopy.WriteToServerAsync.
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Odbc;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace SqlBulkCopyAsyncCodeSample {
class Program {
static string selectStatement = "SELECT * FROM [pubs].[dbo].[titles]";
static string createDestTableStatement =
@"CREATE TABLE {0} (
[title_id] [varchar](6) NOT NULL,
[title] [varchar](80) NOT NULL,
[type] [char](12) NOT NULL,
[pub_id] [char](4) NULL,
[price] [money] NULL,
[advance] [money] NULL,
[royalty] [int] NULL,
[ytd_sales] [int] NULL,
[notes] [varchar](200) NULL,
[pubdate] [datetime] NOT NULL)";
// Replace the connection string if needed, for instance to connect to SQL Express: @"Server=(local)\SQLEXPRESS;Database=Demo;Integrated Security=true"
// static string connectionString = @"Server=(localdb)\V11.0;Database=Demo";
static string connectionString = @"Server=(local);Database=Demo;Integrated Security=true";
// static string odbcConnectionString = @"Driver={SQL Server};Server=(localdb)\V11.0;UID=oledb;Pwd=[PLACEHOLDER];Database=Demo";
static string odbcConnectionString = @"Driver={SQL Server};Server=(local);Database=Demo;Integrated Security=true";
// static string marsConnectionString = @"Server=(localdb)\V11.0;Database=Demo;MultipleActiveResultSets=true;";
static string marsConnectionString = @"Server=(local);Database=Demo;MultipleActiveResultSets=true;Integrated Security=true";
// Replace the Server name with your actual sql azure server name and User ID/Password
static string azureConnectionString = @"Server=SqlAzure;User ID=myUserID;Password=myPassword;Database=Demo";
static void Main(string[] args) {
SynchronousSqlBulkCopy();
AsyncSqlBulkCopy().Wait();
MixSyncAsyncSqlBulkCopy().Wait();
AsyncSqlBulkCopyNotifyAfter().Wait();
AsyncSqlBulkCopyDataRows().Wait();
// AsyncSqlBulkCopySqlServerToSqlAzure().Wait();
// AsyncSqlBulkCopyCancel().Wait();
AsyncSqlBulkCopyMARS().Wait();
}
// 3.1.1 Synchronous bulk copy in .NET Framework 4.5
private static void SynchronousSqlBulkCopy() {
using (SqlConnection conn = new SqlConnection(connectionString)) {
conn.Open();
DataTable dt = new DataTable();
using (SqlCommand cmd = new SqlCommand(selectStatement, conn)) {
SqlDataAdapter adapter = new SqlDataAdapter(cmd);
adapter.Fill(dt);
string temptable = "[#" + Guid.NewGuid().ToString("N") + "]";
cmd.CommandText = string.Format(createDestTableStatement, temptable);
cmd.ExecuteNonQuery();
using (SqlBulkCopy bcp = new SqlBulkCopy(conn)) {
bcp.DestinationTableName = temptable;
bcp.WriteToServer(dt);
}
}
}
}
// 3.1.2 Asynchronous bulk copy in .NET Framework 4.5
private static async Task AsyncSqlBulkCopy() {
using (SqlConnection conn = new SqlConnection(connectionString)) {
await conn.OpenAsync();
DataTable dt = new DataTable();
using (SqlCommand cmd = new SqlCommand(selectStatement, conn)) {
SqlDataAdapter adapter = new SqlDataAdapter(cmd);
adapter.Fill(dt);
string temptable = "[#" + Guid.NewGuid().ToString("N") + "]";
cmd.CommandText = string.Format(createDestTableStatement, temptable);
await cmd.ExecuteNonQueryAsync();
using (SqlBulkCopy bcp = new SqlBulkCopy(conn)) {
bcp.DestinationTableName = temptable;
await bcp.WriteToServerAsync(dt);
}
}
}
}
// 3.2 Add new Async.NET capabilities in an existing application (Mixing synchronous and asynchronous calls)
private static async Task MixSyncAsyncSqlBulkCopy() {
using (OdbcConnection odbcconn = new OdbcConnection(odbcConnectionString)) {
odbcconn.Open();
using (OdbcCommand odbccmd = new OdbcCommand(selectStatement, odbcconn)) {
using (OdbcDataReader odbcreader = odbccmd.ExecuteReader()) {
using (SqlConnection conn = new SqlConnection(connectionString)) {
await conn.OpenAsync();
string temptable = "temptable";//"[#" + Guid.NewGuid().ToString("N") + "]";
SqlCommand createCmd = new SqlCommand(string.Format(createDestTableStatement, temptable), conn);
await createCmd.ExecuteNonQueryAsync();
using (SqlBulkCopy bcp = new SqlBulkCopy(conn)) {
bcp.DestinationTableName = temptable;
await bcp.WriteToServerAsync(odbcreader);
}
}
}
}
}
}
// 3.3 Using the NotifyAfter property
private static async Task AsyncSqlBulkCopyNotifyAfter() {
using (SqlConnection conn = new SqlConnection(connectionString)) {
await conn.OpenAsync();
DataTable dt = new DataTable();
using (SqlCommand cmd = new SqlCommand(selectStatement, conn)) {
SqlDataAdapter adapter = new SqlDataAdapter(cmd);
adapter.Fill(dt);
string temptable = "[#" + Guid.NewGuid().ToString("N") + "]";
cmd.CommandText = string.Format(createDestTableStatement, temptable);
await cmd.ExecuteNonQueryAsync();
using (SqlBulkCopy bcp = new SqlBulkCopy(conn)) {
bcp.DestinationTableName = temptable;
bcp.NotifyAfter = 5;
bcp.SqlRowsCopied += new SqlRowsCopiedEventHandler(OnSqlRowsCopied);
await bcp.WriteToServerAsync(dt);
}
}
}
}
private static void OnSqlRowsCopied(object sender, SqlRowsCopiedEventArgs e) {
Console.WriteLine("Copied {0} so far...", e.RowsCopied);
}
// 3.4 Using the new SqlBulkCopy Async.NET capabilities with DataRow[]
private static async Task AsyncSqlBulkCopyDataRows() {
using (SqlConnection conn = new SqlConnection(connectionString)) {
await conn.OpenAsync();
DataTable dt = new DataTable();
using (SqlCommand cmd = new SqlCommand(selectStatement, conn)) {
SqlDataAdapter adapter = new SqlDataAdapter(cmd);
adapter.Fill(dt);
DataRow[] rows = dt.Select();
string temptable = "[#" + Guid.NewGuid().ToString("N") + "]";
cmd.CommandText = string.Format(createDestTableStatement, temptable);
await cmd.ExecuteNonQueryAsync();
using (SqlBulkCopy bcp = new SqlBulkCopy(conn)) {
bcp.DestinationTableName = temptable;
await bcp.WriteToServerAsync(rows);
}
}
}
}
// 3.5 Copying data from SQL Server to SQL Azure in .NET Framework 4.5
//private static async Task AsyncSqlBulkCopySqlServerToSqlAzure() {
// using (SqlConnection srcConn = new SqlConnection(connectionString))
// using (SqlConnection destConn = new SqlConnection(azureConnectionString)) {
// await srcConn.OpenAsync();
// await destConn.OpenAsync();
// using (SqlCommand srcCmd = new SqlCommand(selectStatement, srcConn)) {
// using (SqlDataReader reader = await srcCmd.ExecuteReaderAsync()) {
// string temptable = "[#" + Guid.NewGuid().ToString("N") + "]";
// using (SqlCommand destCmd = new SqlCommand(string.Format(createDestTableStatement, temptable), destConn)) {
// await destCmd.ExecuteNonQueryAsync();
// using (SqlBulkCopy bcp = new SqlBulkCopy(destConn)) {
// bcp.DestinationTableName = temptable;
// await bcp.WriteToServerAsync(reader);
// }
// }
// }
// }
// }
//}
// 3.6 Cancelling an Asynchronous Operation to SQL Azure
//private static async Task AsyncSqlBulkCopyCancel() {
// CancellationTokenSource cts = new CancellationTokenSource();
// using (SqlConnection srcConn = new SqlConnection(connectionString))
// using (SqlConnection destConn = new SqlConnection(azureConnectionString)) {
// await srcConn.OpenAsync(cts.Token);
// await destConn.OpenAsync(cts.Token);
// using (SqlCommand srcCmd = new SqlCommand(selectStatement, srcConn)) {
// using (SqlDataReader reader = await srcCmd.ExecuteReaderAsync(cts.Token)) {
// string temptable = "[#" + Guid.NewGuid().ToString("N") + "]";
// using (SqlCommand destCmd = new SqlCommand(string.Format(createDestTableStatement, temptable), destConn)) {
// await destCmd.ExecuteNonQueryAsync(cts.Token);
// using (SqlBulkCopy bcp = new SqlBulkCopy(destConn)) {
// bcp.DestinationTableName = temptable;
// await bcp.WriteToServerAsync(reader, cts.Token);
// //Cancel Async SqlBulCopy Operation after 200 ms
// cts.CancelAfter(200);
// }
// }
// }
// }
// }
//}
// 3.7 Using Async.Net and MARS
private static async Task AsyncSqlBulkCopyMARS() {
using (SqlConnection marsConn = new SqlConnection(marsConnectionString)) {
await marsConn.OpenAsync();
SqlCommand titlesCmd = new SqlCommand("SELECT * FROM [pubs].[dbo].[titles]", marsConn);
SqlCommand authorsCmd = new SqlCommand("SELECT * FROM [pubs].[dbo].[authors]", marsConn);
//With MARS we can have multiple active results sets on the same connection
using (SqlDataReader titlesReader = await titlesCmd.ExecuteReaderAsync())
using (SqlDataReader authorsReader = await authorsCmd.ExecuteReaderAsync()) {
await authorsReader.ReadAsync();
string temptable = "[#" + Guid.NewGuid().ToString("N") + "]";
using (SqlConnection destConn = new SqlConnection(connectionString)) {
await destConn.OpenAsync();
using (SqlCommand destCmd = new SqlCommand(string.Format(createDestTableStatement, temptable), destConn)) {
await destCmd.ExecuteNonQueryAsync();
using (SqlBulkCopy bcp = new SqlBulkCopy(destConn)) {
bcp.DestinationTableName = temptable;
await bcp.WriteToServerAsync(titlesReader);
}
}
}
}
}
}
}
}
Secara Asinkron Menggunakan Beberapa Perintah dengan MARS
Contoh membuka satu koneksi ke database AdventureWorks. Menggunakan SqlCommandobjek , sebuah SqlDataReader dibuat. Saat pembaca digunakan, satu detik SqlDataReader dibuka, menggunakan data dari SqlDataReader yang pertama sebagai input untuk klausul WHERE untuk pembaca kedua.
Catatan
Contoh berikut menggunakan contoh database AdventureWorks yang disertakan dengan SQL Server. String koneksi yang disediakan dalam kode sampel mengasumsikan database dipasang dan tersedia di komputer lokal. Ubah string koneksi seperlunya untuk lingkungan Anda.
using System;
using System.Data;
using System.Data.SqlClient;
using System.Threading.Tasks;
class Class1 {
static void Main() {
Task task = MultipleCommands();
task.Wait();
}
static async Task MultipleCommands() {
// By default, MARS is disabled when connecting to a MARS-enabled.
// It must be enabled in the connection string.
string connectionString = GetConnectionString();
int vendorID;
SqlDataReader productReader = null;
string vendorSQL =
"SELECT VendorId, Name FROM Purchasing.Vendor";
string productSQL =
"SELECT Production.Product.Name FROM Production.Product " +
"INNER JOIN Purchasing.ProductVendor " +
"ON Production.Product.ProductID = " +
"Purchasing.ProductVendor.ProductID " +
"WHERE Purchasing.ProductVendor.VendorID = @VendorId";
using (SqlConnection awConnection =
new SqlConnection(connectionString)) {
SqlCommand vendorCmd = new SqlCommand(vendorSQL, awConnection);
SqlCommand productCmd =
new SqlCommand(productSQL, awConnection);
productCmd.Parameters.Add("@VendorId", SqlDbType.Int);
await awConnection.OpenAsync();
using (SqlDataReader vendorReader = await vendorCmd.ExecuteReaderAsync()) {
while (await vendorReader.ReadAsync()) {
Console.WriteLine(vendorReader["Name"]);
vendorID = (int)vendorReader["VendorId"];
productCmd.Parameters["@VendorId"].Value = vendorID;
// The following line of code requires a MARS-enabled connection.
productReader = await productCmd.ExecuteReaderAsync();
using (productReader) {
while (await productReader.ReadAsync()) {
Console.WriteLine(" " +
productReader["Name"].ToString());
}
}
}
}
}
}
private static string GetConnectionString() {
// To avoid storing the connection string in your code, you can retrieve it from a configuration file.
return "Data Source=(local);Integrated Security=SSPI;Initial Catalog=AdventureWorks;MultipleActiveResultSets=True";
}
}
Membaca dan Memperbarui Data secara Asinkron dengan MARS
MARS memungkinkan koneksi digunakan untuk operasi pembacaan dan operasi bahasa manipulasi data (DML) dengan lebih dari satu operasi yang tertunda. Fitur ini menghilangkan kebutuhan aplikasi akan penanganan kesalahan koneksi-sibuk. Selain itu, MARS dapat menggantikan pengguna kursor sisi server, yang umumnya menghabiskan lebih banyak sumber daya. Akhirnya, karena beberapa operasi dapat dijalankan pada satu koneksi, maka dapat berbagi konteks transaksi yang sama, yang menghilangkan kebutuhan untuk menggunakan prosedur tersimpan sistem sp_getbindtoken dan sp_bindsession.
Aplikasi Konsol berikut menunjukkan cara menggunakan dua objek SqlDataReader dengan tiga objek SqlCommand dan satu objek SqlConnection dengan MARS diaktifkan. Objek perintah pertama mengambil daftar vendor yang nilai kreditnya adalah 5. Objek perintah kedua menggunakan ID vendor yang disediakan dari SqlDataReader untuk memuat SqlDataReader yang kedua dengan semua produk untuk vendor tertentu. Setiap rekaman produk dikunjungi oleh SqlDataReader yang kedua. Penghitungan dilakukan untuk menentukan OnOrderQty baru yang seharusnya. Objek perintah ketiga kemudian digunakan untuk memperbarui tabel ProductVendor dengan nilai baru. Seluruh proses ini terjadi dalam satu transaksi, yang akhirnya digulung balik.
Catatan
Contoh berikut menggunakan contoh database AdventureWorks yang disertakan dengan SQL Server. String koneksi yang disediakan dalam kode sampel mengasumsikan database dipasang dan tersedia di komputer lokal. Ubah string koneksi seperlunya untuk lingkungan Anda.
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.SqlClient;
using System.Threading.Tasks;
class Program {
static void Main() {
Task task = ReadingAndUpdatingData();
task.Wait();
}
static async Task ReadingAndUpdatingData() {
// By default, MARS is disabled when connecting to a MARS-enabled host.
// It must be enabled in the connection string.
string connectionString = GetConnectionString();
SqlTransaction updateTx = null;
SqlCommand vendorCmd = null;
SqlCommand prodVendCmd = null;
SqlCommand updateCmd = null;
SqlDataReader prodVendReader = null;
int vendorID = 0;
int productID = 0;
int minOrderQty = 0;
int maxOrderQty = 0;
int onOrderQty = 0;
int recordsUpdated = 0;
int totalRecordsUpdated = 0;
string vendorSQL =
"SELECT VendorID, Name FROM Purchasing.Vendor " +
"WHERE CreditRating = 5";
string prodVendSQL =
"SELECT ProductID, MaxOrderQty, MinOrderQty, OnOrderQty " +
"FROM Purchasing.ProductVendor " +
"WHERE VendorID = @VendorID";
string updateSQL =
"UPDATE Purchasing.ProductVendor " +
"SET OnOrderQty = @OrderQty " +
"WHERE ProductID = @ProductID AND VendorID = @VendorID";
using (SqlConnection awConnection =
new SqlConnection(connectionString)) {
await awConnection.OpenAsync();
updateTx = await Task.Run(() => awConnection.BeginTransaction());
vendorCmd = new SqlCommand(vendorSQL, awConnection);
vendorCmd.Transaction = updateTx;
prodVendCmd = new SqlCommand(prodVendSQL, awConnection);
prodVendCmd.Transaction = updateTx;
prodVendCmd.Parameters.Add("@VendorId", SqlDbType.Int);
updateCmd = new SqlCommand(updateSQL, awConnection);
updateCmd.Transaction = updateTx;
updateCmd.Parameters.Add("@OrderQty", SqlDbType.Int);
updateCmd.Parameters.Add("@ProductID", SqlDbType.Int);
updateCmd.Parameters.Add("@VendorID", SqlDbType.Int);
using (SqlDataReader vendorReader = await vendorCmd.ExecuteReaderAsync()) {
while (await vendorReader.ReadAsync()) {
Console.WriteLine(vendorReader["Name"]);
vendorID = (int)vendorReader["VendorID"];
prodVendCmd.Parameters["@VendorID"].Value = vendorID;
prodVendReader = await prodVendCmd.ExecuteReaderAsync();
using (prodVendReader) {
while (await prodVendReader.ReadAsync()) {
productID = (int)prodVendReader["ProductID"];
if (prodVendReader["OnOrderQty"] == DBNull.Value) {
minOrderQty = (int)prodVendReader["MinOrderQty"];
onOrderQty = minOrderQty;
}
else {
maxOrderQty = (int)prodVendReader["MaxOrderQty"];
onOrderQty = (int)(maxOrderQty / 2);
}
updateCmd.Parameters["@OrderQty"].Value = onOrderQty;
updateCmd.Parameters["@ProductID"].Value = productID;
updateCmd.Parameters["@VendorID"].Value = vendorID;
recordsUpdated = await updateCmd.ExecuteNonQueryAsync();
totalRecordsUpdated += recordsUpdated;
}
}
}
}
Console.WriteLine("Total Records Updated: ", totalRecordsUpdated.ToString());
await Task.Run(() => updateTx.Rollback());
Console.WriteLine("Transaction Rolled Back");
}
}
private static string GetConnectionString() {
// To avoid storing the connection string in your code, you can retrieve it from a configuration file.
return "Data Source=(local);Integrated Security=SSPI;Initial Catalog=AdventureWorks;MultipleActiveResultSets=True";
}
}