IAsyncEnumerable with yield in C#: sample moved to async-csharp/IAsyncEnumerableWithYield on .NET 10

async-csharp/IAsyncEnumerableWithYield/.gitignore

@@ -0,0 +1,4 @@
+# SQLite database the API creates on first run
+*.db
+*.db-shm
+*.db-wal

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYield.sln

@@ -0,0 +1,90 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
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+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SyncYield", "SyncYield\SyncYield.csproj", "{29FC1E6D-1BB0-4AE1-879B-B97A2BC0AD44}"
+EndProject
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+EndProject
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+EndProject
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+EndProject
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+EndGlobal

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYield/IAsyncEnumerableWithYield.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYield/Program.cs

@@ -0,0 +1,17 @@
+Console.WriteLine($"{DateTime.Now.ToLongTimeString()}: Start");
+
+await foreach (var item in FetchItems())
+{
+    Console.WriteLine($"{DateTime.Now.ToLongTimeString()}: {item}");
+}
+
+Console.WriteLine($"{DateTime.Now.ToLongTimeString()}: End");
+
+static async IAsyncEnumerable<int> FetchItems()
+{
+    for (int i = 1; i <= 10; i++)
+    {
+        await Task.Delay(1000);
+        yield return i;
+    }
+}

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYieldApi/Controllers/ItemsController.cs

@@ -0,0 +1,18 @@
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+
+[Route("api/[controller]")]
+[ApiController]
+public class ItemsController : ControllerBase
+{
+    private readonly ItemContext _context;
+
+    public ItemsController(ItemContext context)
+    {
+        _context = context ?? throw new ArgumentNullException(nameof(context));
+    }
+
+    [HttpGet]
+    public IAsyncEnumerable<Item> GetItems() =>
+        _context.Items.AsNoTracking().AsAsyncEnumerable();
+}

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYieldApi/Controllers/ValuesController.cs

@@ -0,0 +1,21 @@
+using Microsoft.AspNetCore.Mvc;
+
+[Route("api/[controller]")]
+[ApiController]
+public class ValuesController : ControllerBase
+{
+    [HttpGet]
+    public IAsyncEnumerable<int> Get()
+    {
+        return FetchItems();
+    }
+
+    static async IAsyncEnumerable<int> FetchItems()
+    {
+        for (int i = 1; i <= 10; i++)
+        {
+            await Task.Delay(1000);
+            yield return i;
+        }
+    }
+}

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYieldApi/Data/Item.cs

@@ -0,0 +1,5 @@
+public class Item
+{
+    public int Id { get; set; }
+    public string Name { get; set; } = string.Empty;
+}

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYieldApi/Data/ItemContext.cs

@@ -0,0 +1,6 @@
+using Microsoft.EntityFrameworkCore;
+
+public class ItemContext(DbContextOptions<ItemContext> options) : DbContext(options)
+{
+    public DbSet<Item> Items => Set<Item>();
+}

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYieldApi/IAsyncEnumerableWithYieldApi.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="10.0.12" />
+  </ItemGroup>
+
+</Project>

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYieldApi/Program.cs

@@ -0,0 +1,39 @@
+using Microsoft.EntityFrameworkCore;
+
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Services.AddControllers();
+builder.Services.AddDbContext<ItemContext>(options =>
+    options.UseSqlite(builder.Configuration.GetConnectionString("Items")));
+
+var app = builder.Build();
+
+using (var scope = app.Services.CreateScope())
+{
+    var context = scope.ServiceProvider.GetRequiredService<ItemContext>();
+    context.Database.EnsureCreated();
+
+    if (!context.Items.Any())
+    {
+        context.Items.AddRange(
+            new Item { Name = "Keyboard" },
+            new Item { Name = "Mouse" },
+            new Item { Name = "Monitor" });
+        context.SaveChanges();
+    }
+}
+
+app.MapControllers();
+
+app.MapGet("/items", () => FetchItems());
+
+app.Run();
+
+static async IAsyncEnumerable<int> FetchItems()
+{
+    for (var i = 1; i <= 10; i++)
+    {
+        await Task.Delay(1000);
+        yield return i;
+    }
+}

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYieldApi/Properties/launchSettings.json

@@ -0,0 +1,15 @@
+{
+  "$schema": "https://json.schemastore.org/launchsettings.json",
+  "profiles": {
+    "https": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": true,
+      "launchUrl": "api/values",
+      "applicationUrl": "https://localhost:5001;http://localhost:5000",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    }
+  }
+}

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYieldApi/appsettings.Development.json

@@ -0,0 +1,8 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  }
+}

async-csharp/IAsyncEnumerableWithYield/IAsyncEnumerableWithYieldApi/appsettings.json

@@ -0,0 +1,12 @@
+{
+  "ConnectionStrings": {
+    "Items": "Data Source=items.db"
+  },
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  },
+  "AllowedHosts": "*"
+}

async-csharp/IAsyncEnumerableWithYield/SyncYield/Program.cs

@@ -0,0 +1,17 @@
+Console.WriteLine($"{DateTime.Now.ToLongTimeString()}: Start");
+
+foreach (var item in FetchItems())
+{
+    Console.WriteLine($"{DateTime.Now.ToLongTimeString()}: {item}");
+}
+
+Console.WriteLine($"{DateTime.Now.ToLongTimeString()}: End");
+
+static IEnumerable<int> FetchItems()
+{
+    for (int i = 1; i <= 10; i++)
+    {
+        Thread.Sleep(1000);
+        yield return i;
+    }
+}

async-csharp/IAsyncEnumerableWithYield/SyncYield/SyncYield.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

async-csharp/IAsyncEnumerableWithYield/TaskOfIEnumerable/Program.cs

@@ -0,0 +1,20 @@
+Console.WriteLine($"{DateTime.Now.ToLongTimeString()}: Start");
+
+foreach (var item in await FetchItems())
+{
+    Console.WriteLine($"{DateTime.Now.ToLongTimeString()}: {item}");
+}
+
+Console.WriteLine($"{DateTime.Now.ToLongTimeString()}: End");
+
+static async Task<IEnumerable<int>> FetchItems()
+{
+    List<int> Items = new List<int>();
+    for (int i = 1; i <= 10; i++)
+    {
+        await Task.Delay(1000);
+        Items.Add(i);
+    }
+
+    return Items;
+}

async-csharp/IAsyncEnumerableWithYield/TaskOfIEnumerable/TaskOfIEnumerable.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

async-csharp/IAsyncEnumerableWithYield/Tests/AsAsyncEnumerableUnitTest.cs

@@ -0,0 +1,53 @@
+using System.Data.Common;
+using Microsoft.Data.Sqlite;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Diagnostics;
+
+namespace Tests;
+
+[TestClass]
+public class AsAsyncEnumerableUnitTest
+{
+    [TestMethod]
+    public async Task GivenItemsQuery_WhenAsAsyncEnumerableIsCalled_ThenNoCommandRunsUntilEnumeration()
+    {
+        await using var connection = new SqliteConnection("Data Source=:memory:");
+        await connection.OpenAsync();
+
+        var counter = new ReaderCounter();
+        var options = new DbContextOptionsBuilder<ItemContext>()
+            .UseSqlite(connection)
+            .AddInterceptors(counter)
+            .Options;
+
+        await using var context = new ItemContext(options);
+        await context.Database.EnsureCreatedAsync();
+        context.Items.AddRange(new Item { Name = "Keyboard" }, new Item { Name = "Mouse" });
+        await context.SaveChangesAsync();
+        counter.Readers = 0;
+
+        var items = context.Items.AsNoTracking().AsAsyncEnumerable();
+        await using var enumerator = items.GetAsyncEnumerator();
+
+        Assert.AreEqual(0, counter.Readers);
+
+        Assert.IsTrue(await enumerator.MoveNextAsync());
+        Assert.AreEqual(1, counter.Readers);
+        Assert.AreEqual("Keyboard", enumerator.Current.Name);
+    }
+
+    private sealed class ReaderCounter : DbCommandInterceptor
+    {
+        public int Readers;
+
+        public override ValueTask<InterceptionResult<DbDataReader>> ReaderExecutingAsync(
+            DbCommand command,
+            CommandEventData eventData,
+            InterceptionResult<DbDataReader> result,
+            CancellationToken cancellationToken = default)
+        {
+            Readers++;
+            return base.ReaderExecutingAsync(command, eventData, result, cancellationToken);
+        }
+    }
+}