Dukungan streaming SqlClient
Dukungan streaming antara SQL Server dan aplikasi (baru di .NET Framework 4.5) mendukung data tidak terstruktur di server (dokumen, gambar, dan file media). Database SQL Server dapat menyimpan objek besar biner (BLOB), tetapi mengambil BLOBS dapat menggunakan banyak memori.
Dukungan streaming ke dan dari SQL Server menyederhanakan penulisan aplikasi yang mengalirkan data, tanpa harus memuat data secara penuh ke dalam memori, menghasilkan lebih sedikit pengecualian memori yang meluap.
Dukungan streaming juga akan memungkinkan aplikasi tingkat menengah untuk skala lebih baik, terutama dalam skenario ketika objek bisnis terhubung ke SQL Azure untuk mengirim, mengambil, dan memanipulasi BLOB besar.
Peringatan
Panggilan asinkron tidak didukung jika aplikasi juga menggunakan kata kunci string koneksi Context Connection.
Anggota yang ditambahkan untuk mendukung streaming digunakan untuk mengambil data dari kueri dan untuk meneruskan parameter ke kueri dan prosedur tersimpan. Fitur streaming membahas OLTP dasar dan skenario migrasi data dan berlaku untuk lingkungan migrasi data di tempat dan di luar tempat.
Dukungan Streaming dari SQL Server
Dukungan streaming dari SQL Server memperkenalkan fungsionalitas baru di kelas DbDataReader dan SqlDataReader untuk mendapatkan objek Stream, XmlReader, dan TextReader dan bereaksi terhadapnya. Kelas-kelas ini digunakan untuk mengambil data dari kueri. Akibatnya, dukungan Streaming dari SQL Server menangani skenario OLTP dan berlaku untuk lingkungan di tempat dan di luar tempat.
Anggota berikut ditambahkan ke SqlDataReader untuk mengaktifkan dukungan streaming dari SQL Server:
Anggota berikut ditambahkan ke DbDataReader untuk mengaktifkan dukungan streaming dari SQL Server:
Dukungan Streaming ke SQL Server
Dukungan streaming ke SQL Server memperkenalkan fungsionalitas baru di kelas SqlParameter sehingga dapat menerima dan bereaksi terhadap objek XmlReader, Stream, dan TextReader. SqlParameter digunakan untuk meneruskan parameter ke kueri dan prosedur tersimpan.
Membuang objek SqlCommand atau memanggil Cancel harus membatalkan operasi streaming apa pun. Jika aplikasi mengirimkan CancellationToken, pembatalan tidak dijamin.
Jenis SqlDbType berikut akan menerima Value dari Stream:
- Biner
- VarBinary
Jenis SqlDbType berikut akan menerima Value dari TextReader:
- Char
- NChar
- NVarChar
- Xml
Jenis XmlSqlDbType akan menerima Value dari XmlReader.
SqlValue dapat menerima nilai jenis XmlReader, TextReader, dan Stream.
Objek XmlReader, TextReader, dan Stream akan ditransfer hingga nilai yang ditentukan oleh Size.
Sampel: Streaming dari SQL Server
Gunakan Transact-SQL berikut untuk membuat database sampel:
CREATE DATABASE [Demo]
GO
USE [Demo]
GO
CREATE TABLE [Streams] (
[id] INT PRIMARY KEY IDENTITY(1, 1),
[textdata] NVARCHAR(MAX),
[bindata] VARBINARY(MAX),
[xmldata] XML)
GO
INSERT INTO [Streams] (textdata, bindata, xmldata) VALUES (N'This is a test', 0x48656C6C6F, N'<test>value</test>')
INSERT INTO [Streams] (textdata, bindata, xmldata) VALUES (N'Hello, World!', 0x54657374696E67, N'<test>value2</test>')
INSERT INTO [Streams] (textdata, bindata, xmldata) VALUES (N'Another row', 0x666F6F626172, N'<fff>bbb</fff><fff>bbc</fff>')
GO
Sampel menunjukkan cara melakukan hal berikut:
- Hindari memblokir utas antarmuka pengguna dengan menyediakan cara asinkron untuk mengambil file besar.
- Transfer file teks besar dari SQL Server di .NET Framework 4.5.
- Transfer file XML besar dari SQL Server di .NET Framework 4.5.
- Ambil data dari SQL Server.
- Transfer file besar (BLOB) dari satu database SQL Server ke database lain tanpa kehabisan memori.
using System;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Threading.Tasks;
using System.Xml;
namespace StreamingFromServer {
class Program {
private const string connectionString = @"...";
static void Main(string[] args) {
CopyBinaryValueToFile().Wait();
PrintTextValues().Wait();
PrintXmlValues().Wait();
PrintXmlValuesViaNVarChar().Wait();
Console.WriteLine("Done");
}
// Retrieve a large BLOB from SQL Server in .NET Framework 4.5 using the asynchronous capability.
private static async Task CopyBinaryValueToFile() {
string filePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), "binarydata.bin");
using (SqlConnection connection = new SqlConnection(connectionString)) {
await connection.OpenAsync();
using (SqlCommand command = new SqlCommand("SELECT [bindata] FROM [Streams] WHERE [id]=@id", connection)) {
command.Parameters.AddWithValue("id", 1);
// The reader needs to be executed with the SequentialAccess behavior to enable network streaming.
// Otherwise ReadAsync will buffer the entire BLOB into memory which can cause scalability issues or even OutOfMemoryExceptions.
using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.SequentialAccess)) {
if (await reader.ReadAsync()) {
if (!(await reader.IsDBNullAsync(0))) {
using (FileStream file = new FileStream(filePath, FileMode.Create, FileAccess.Write)) {
using (Stream data = reader.GetStream(0)) {
// Asynchronously copy the stream from the server to the file we just created.
await data.CopyToAsync(file);
}
}
}
}
}
}
}
}
// Transfer a large Text File from SQL Server in .NET Framework 4.5.
private static async Task PrintTextValues() {
using (SqlConnection connection = new SqlConnection(connectionString)) {
await connection.OpenAsync();
using (SqlCommand command = new SqlCommand("SELECT [id], [textdata] FROM [Streams]", connection)) {
// The reader needs to be executed with the SequentialAccess behavior to enable network streaming.
// Otherwise ReadAsync will buffer the entire text document into memory which can cause scalability issues or even OutOfMemoryExceptions.
using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.SequentialAccess)) {
while (await reader.ReadAsync()) {
Console.Write("{0}: ", reader.GetInt32(0));
if (await reader.IsDBNullAsync(1)) {
Console.Write("(NULL)");
}
else {
char[] buffer = new char[4096];
int charsRead = 0;
using (TextReader data = reader.GetTextReader(1)) {
do {
// Grab each chunk of text and write it to the console.
// If you are writing to a TextWriter, you should use WriteAsync or WriteLineAsync.
charsRead = await data.ReadAsync(buffer, 0, buffer.Length);
Console.Write(buffer, 0, charsRead);
} while (charsRead > 0);
}
}
Console.WriteLine();
}
}
}
}
}
// Transfer a large Xml Document from SQL Server in .NET Framework 4.5.
private static async Task PrintXmlValues() {
using (SqlConnection connection = new SqlConnection(connectionString)) {
await connection.OpenAsync();
using (SqlCommand command = new SqlCommand("SELECT [id], [xmldata] FROM [Streams]", connection)) {
// The reader needs to be executed with the SequentialAccess behavior to enable network streaming.
// Otherwise ReadAsync will buffer the entire Xml Document into memory which can cause scalability issues or even OutOfMemoryExceptions.
using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.SequentialAccess)) {
while (await reader.ReadAsync()) {
Console.WriteLine("{0}: ", reader.GetInt32(0));
if (await reader.IsDBNullAsync(1)) {
Console.WriteLine("\t(NULL)");
}
else {
using (XmlReader xmlReader = reader.GetXmlReader(1)) {
int depth = 1;
// NOTE: The XmlReader returned by GetXmlReader does NOT support async operations.
// See the example below (PrintXmlValuesViaNVarChar) for how to get an XmlReader with asynchronous capabilities.
while (xmlReader.Read()) {
switch (xmlReader.NodeType) {
case XmlNodeType.Element:
Console.WriteLine("{0}<{1}>", new string('\t', depth), xmlReader.Name);
depth++;
break;
case XmlNodeType.Text:
Console.WriteLine("{0}{1}", new string('\t', depth), xmlReader.Value);
break;
case XmlNodeType.EndElement:
depth--;
Console.WriteLine("{0}</{1}>", new string('\t', depth), xmlReader.Name);
break;
}
}
}
}
}
}
}
}
}
// Transfer a large Xml Document from SQL Server in .NET Framework 4.5.
// This goes via NVarChar and TextReader to enable asynchronous reading.
private static async Task PrintXmlValuesViaNVarChar() {
XmlReaderSettings xmlSettings = new XmlReaderSettings() {
// Async must be explicitly enabled in the XmlReaderSettings otherwise the XmlReader will throw exceptions when async methods are called.
Async = true,
// Since we will immediately wrap the TextReader we are creating in an XmlReader, we will permit the XmlReader to take care of closing\disposing it.
CloseInput = true,
// If the Xml you are reading is not a valid document (as per <https://learn.microsoft.com/previous-versions/dotnet/netframework-4.0/6bts1x50(v=vs.100)>) you will need to set the conformance level to Fragment.
ConformanceLevel = ConformanceLevel.Fragment
};
using (SqlConnection connection = new SqlConnection(connectionString)) {
await connection.OpenAsync();
// Cast the XML into NVarChar to enable GetTextReader - trying to use GetTextReader on an XML type will throw an exception.
using (SqlCommand command = new SqlCommand("SELECT [id], CAST([xmldata] AS NVARCHAR(MAX)) FROM [Streams]", connection)) {
// The reader needs to be executed with the SequentialAccess behavior to enable network streaming.
// Otherwise ReadAsync will buffer the entire Xml Document into memory which can cause scalability issues or even OutOfMemoryExceptions.
using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.SequentialAccess)) {
while (await reader.ReadAsync()) {
Console.WriteLine("{0}:", reader.GetInt32(0));
if (await reader.IsDBNullAsync(1)) {
Console.WriteLine("\t(NULL)");
}
else {
// Grab the row as a TextReader, then create an XmlReader on top of it.
// The code doesn't keep a reference to the TextReader since the XmlReader is created with the "CloseInput" setting (so it will close the TextReader when needed).
using (XmlReader xmlReader = XmlReader.Create(reader.GetTextReader(1), xmlSettings)) {
int depth = 1;
// The XmlReader above now supports asynchronous operations, so we can use ReadAsync here.
while (await xmlReader.ReadAsync()) {
switch (xmlReader.NodeType) {
case XmlNodeType.Element:
Console.WriteLine("{0}<{1}>", new string('\t', depth), xmlReader.Name);
depth++;
break;
case XmlNodeType.Text:
// Depending on what your data looks like, you should either use Value or GetValueAsync.
// Value has less overhead (since it doesn't create a Task), but it may also block if additional data is required.
Console.WriteLine("{0}{1}", new string('\t', depth), await xmlReader.GetValueAsync());
break;
case XmlNodeType.EndElement:
depth--;
Console.WriteLine("{0}</{1}>", new string('\t', depth), xmlReader.Name);
break;
}
}
}
}
}
}
}
}
}
}
}
Sampel: Streaming ke SQL Server
Gunakan Transact-SQL berikut untuk membuat database sampel:
CREATE DATABASE [Demo2]
GO
USE [Demo2]
GO
CREATE TABLE [BinaryStreams] (
[id] INT PRIMARY KEY IDENTITY(1, 1),
[bindata] VARBINARY(MAX))
GO
CREATE TABLE [TextStreams] (
[id] INT PRIMARY KEY IDENTITY(1, 1),
[textdata] NVARCHAR(MAX))
GO
CREATE TABLE [BinaryStreamsCopy] (
[id] INT PRIMARY KEY IDENTITY(1, 1),
[bindata] VARBINARY(MAX))
GO
Sampel menunjukkan cara melakukan hal berikut:
- Transfer BLOB besar ke SQL Server di .NET Framework 4.5.
- Transfer file teks besar ke SQL Server di .NET Framework 4.5.
- Gunakan fitur asinkron baru untuk mentransfer BLOB besar.
- Gunakan fitur asinkron baru dan kata kunci tunggu untuk mentransfer BLOB besar.
- Batalkan transfer BLOB besar.
- Streaming dari satu SQL Server ke SQL Server lainnya menggunakan fitur asinkron baru.
using System;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
namespace StreamingToServer {
class Program {
private const string connectionString = @"...";
static void Main(string[] args) {
CreateDemoFiles();
StreamBLOBToServer().Wait();
StreamTextToServer().Wait();
// Create a CancellationTokenSource that will be cancelled after 100ms
// Typically this token source will be cancelled by a user request (e.g. a Cancel button).
CancellationTokenSource tokenSource = new CancellationTokenSource();
tokenSource.CancelAfter(100);
try {
CancelBLOBStream(tokenSource.Token).Wait();
}
catch (AggregateException ex) {
// Cancelling an async operation will throw an exception.
// Since we are using the Task's Wait method, this exception will be wrapped in an AggregateException.
// If you were using the 'await' keyword, the compiler would take care of unwrapping the AggregateException.
// Depending on when the cancellation occurs, you can either get an error from SQL Server or from .Net.
if ((ex.InnerException is SqlException) || (ex.InnerException is TaskCanceledException)) {
// This is an expected exception.
Console.WriteLine("Got expected exception: {0}", ex.InnerException.Message);
}
else {
// Did not expect this exception - rethrow it.
throw;
}
}
Console.WriteLine("Done");
}
// This is used to generate the files which are used by the other sample methods.
private static void CreateDemoFiles() {
Random rand = new Random();
byte[] data = new byte[1024];
rand.NextBytes(data);
using (FileStream file = File.Open("binarydata.bin", FileMode.Create)) {
file.Write(data, 0, data.Length);
}
using (StreamWriter writer = new StreamWriter(File.Open("textdata.txt", FileMode.Create))) {
writer.Write(Convert.ToBase64String(data));
}
}
// Transfer a large BLOB to SQL Server in .NET Framework 4.5.
private static async Task StreamBLOBToServer() {
using (SqlConnection conn = new SqlConnection(connectionString)) {
await conn.OpenAsync();
using (SqlCommand cmd = new SqlCommand("INSERT INTO [BinaryStreams] (bindata) VALUES (@bindata)", conn)) {
using (FileStream file = File.Open("binarydata.bin", FileMode.Open)) {
// Add a parameter which uses the FileStream we just opened
// Size is set to -1 to indicate "MAX".
cmd.Parameters.Add("@bindata", SqlDbType.Binary, -1).Value = file;
// Send the data to the server asynchronously.
await cmd.ExecuteNonQueryAsync();
}
}
}
}
// Transfer a large Text File to SQL Server in .NET Framework 4.5.
private static async Task StreamTextToServer() {
using (SqlConnection conn = new SqlConnection(connectionString)) {
await conn.OpenAsync();
using (SqlCommand cmd = new SqlCommand("INSERT INTO [TextStreams] (textdata) VALUES (@textdata)", conn)) {
using (StreamReader file = File.OpenText("textdata.txt")) {
// Add a parameter which uses the StreamReader we just opened.
// Size is set to -1 to indicate "MAX".
cmd.Parameters.Add("@textdata", SqlDbType.NVarChar, -1).Value = file;
// Send the data to the server asynchronously.
await cmd.ExecuteNonQueryAsync();
}
}
}
}
// Cancel the transfer of a large BLOB.
private static async Task CancelBLOBStream(CancellationToken cancellationToken) {
using (SqlConnection conn = new SqlConnection(connectionString)) {
// We can cancel not only sending the data to the server, but also opening the connection.
await conn.OpenAsync(cancellationToken);
// Artificially delay the command by 100ms.
using (SqlCommand cmd = new SqlCommand("WAITFOR DELAY '00:00:00:100';INSERT INTO [BinaryStreams] (bindata) VALUES (@bindata)", conn)) {
using (FileStream file = File.Open("binarydata.bin", FileMode.Open)) {
// Add a parameter which uses the FileStream we just opened.
// Size is set to -1 to indicate "MAX".
cmd.Parameters.Add("@bindata", SqlDbType.Binary, -1).Value = file;
// Send the data to the server asynchronously.
// Pass the cancellation token such that the command will be cancelled if needed.
await cmd.ExecuteNonQueryAsync(cancellationToken);
}
}
}
}
}
}
Sampel: Streaming Dari Satu SQL Server ke SQL Server Lain
Contoh ini menunjukkan cara melakukan streaming BLOB besar secara asinkron dari satu SQL Server ke SQL Server lainnya, dengan dukungan untuk pembatalan.
using System;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
namespace StreamingFromServerToAnother {
class Program {
private const string connectionString = @"...";
static void Main(string[] args) {
// For this example, we don't want to cancel,
// so pass in a "blank" cancellation token.
E2EStream(CancellationToken.None).Wait();
Console.WriteLine("Done");
}
// Streaming from one SQL Server to Another One using the new Async.NET.
private static async Task E2EStream(CancellationToken cancellationToken) {
using (SqlConnection readConn = new SqlConnection(connectionString)) {
using (SqlConnection writeConn = new SqlConnection(connectionString)) {
// Note that we are using the same cancellation token for calls to both connections\commands.
// Also we can start both the connection opening asynchronously, and then wait for both to complete.
Task openReadConn = readConn.OpenAsync(cancellationToken);
Task openWriteConn = writeConn.OpenAsync(cancellationToken);
await Task.WhenAll(openReadConn, openWriteConn);
using (SqlCommand readCmd = new SqlCommand("SELECT [bindata] FROM [BinaryStreams]", readConn)) {
using (SqlCommand writeCmd = new SqlCommand("INSERT INTO [BinaryStreamsCopy] (bindata) VALUES (@bindata)", writeConn)) {
// Add an empty parameter to the write command which will be used for the streams we are copying.
// Size is set to -1 to indicate "MAX".
SqlParameter streamParameter = writeCmd.Parameters.Add("@bindata", SqlDbType.Binary, -1);
// The reader needs to be executed with the SequentialAccess behavior to enable network streaming.
// Otherwise ReadAsync will buffer the entire BLOB into memory which can cause scalability issues or even OutOfMemoryExceptions.
using (SqlDataReader reader = await readCmd.ExecuteReaderAsync(CommandBehavior.SequentialAccess, cancellationToken)) {
while (await reader.ReadAsync(cancellationToken)) {
// Grab a stream to the binary data in the source database.
using (Stream dataStream = reader.GetStream(0)) {
// Set the parameter value to the stream source that was opened.
streamParameter.Value = dataStream;
// Asynchronously send data from one database to another.
await writeCmd.ExecuteNonQueryAsync(cancellationToken);
}
}
}
}
}
}
}
}
}
}