Feature: Projections

.config/dotnet-tools.json

@@ -0,0 +1,12 @@
+{
+  "version": 1,
+  "isRoot": true,
+  "tools": {
+    "dotnet-reportgenerator-globaltool": {
+      "version": "5.1.2",
+      "commands": [
+        "reportgenerator"
+      ]
+    }
+  }
+}

.gitignore

@@ -1,5 +1,5 @@
 TestResults
-CoverageResults
+CoverageReport
 
 ## Ignore Visual Studio temporary files, build results, and
 ## files generated by popular Visual Studio add-ons.

generate-coverage-report.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+rm -rf ./TestResults ./CoverageReport
+dotnet tool restore
+dotnet restore EntityDb.sln --locked-mode
+#dotnet test EntityDb.sln --no-restore -c Debug --collect:"XPlat Code Coverage" -r ./TestResults -- DataCollectionRunSettings.DataCollectors.DataCollector.Configuration.Format=opencover
+#dotnet reportgenerator -reports:"./TestResults/**/coverage.opencover.xml" -targetdir:"CoverageReport" -reporttypes:Html -license:"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"
+dotnet test EntityDb.sln --no-restore -c Debug --collect:"XPlat Code Coverage" -r ./TestResults
+dotnet reportgenerator -reports:"./TestResults/**/coverage.cobertura.xml" -targetdir:"CoverageReport" -reporttypes:Html -license:"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"
+open CoverageReport/index.html

src/EntityDb.Abstractions/Projections/IProjectionRepository.cs

@@ -0,0 +1,36 @@
+using EntityDb.Abstractions.Disposables;
+using EntityDb.Abstractions.Snapshots;
+using EntityDb.Abstractions.Transactions;
+using EntityDb.Abstractions.ValueObjects;
+using System.Threading.Tasks;
+
+namespace EntityDb.Abstractions.Projections;
+
+/// <summary>
+///     Encapsulates the snapshot repository for a projection.
+/// </summary>
+/// <typeparam name="TProjection">The type of the projection.</typeparam>
+public interface IProjectionRepository<TProjection> : IDisposableResource
+{
+    /// <summary>
+    ///     The strategy for mapping between projection id and entity id.
+    /// </summary>
+    IProjectionStrategy<TProjection> ProjectionStrategy { get; }
+
+    /// <summary>
+    ///     The backing transaction repository.
+    /// </summary>
+    ITransactionRepository TransactionRepository { get; }
+
+    /// <summary>
+    ///     The backing snapshot repository.
+    /// </summary>
+    ISnapshotRepository<TProjection> SnapshotRepository { get; }
+
+    /// <summary>
+    ///     Returns the current state of a <typeparamref name="TProjection" />.
+    /// </summary>
+    /// <param name="projectionId">The id of the projection.</param>
+    /// <returns>The current state of a <typeparamref name="TProjection" />.</returns>
+    Task<TProjection> GetCurrent(Id projectionId);
+}

src/EntityDb.Abstractions/Projections/IProjectionRepositoryFactory.cs

@@ -0,0 +1,19 @@
+using System.Threading.Tasks;
+
+namespace EntityDb.Abstractions.Projections;
+
+/// <summary>
+///     Represents a type used to create instances of <see cref="IProjectionRepository{TProjection}" />
+/// </summary>
+/// <typeparam name="TProjection">The type of projection managed by the <see cref="IProjectionRepository{TProjection}" />.</typeparam>
+public interface IProjectionRepositoryFactory<TProjection>
+{
+    /// <summary>
+    ///     Create a new instance of <see cref="IProjectionRepository{TProjection}" />
+    /// </summary>
+    /// <param name="transactionSessionOptionsName">The agent's use case for the transaction repository.</param>
+    /// <param name="snapshotSessionOptionsName">The agent's use case for the snapshot repository.</param>
+    /// <returns>A new instance of <see cref="IProjectionRepository{TProjection}" />.</returns>
+    Task<IProjectionRepository<TProjection>> CreateRepository(string transactionSessionOptionsName,
+        string snapshotSessionOptionsName);
+}

src/EntityDb.Abstractions/Projections/IProjectionStrategy.cs

@@ -0,0 +1,26 @@
+using EntityDb.Abstractions.ValueObjects;
+using System.Threading.Tasks;
+
+namespace EntityDb.Abstractions.Projections;
+
+/// <summary>
+///     Represents a type that can map a projection it to a set of entity ids.
+/// </summary>
+/// <typeparam name="TProjection"></typeparam>
+public interface IProjectionStrategy<in TProjection>
+{
+    /// <summary>
+    ///     Map a projection id to a set of entity ids. 
+    /// </summary>
+    /// <param name="projectionId">The id of the projection.</param>
+    /// <param name="projectionSnapshot">A snapshot of the projection, if one exists. (This can be used to avoid running a query, if one were necessary.)</param>
+    /// <returns>The set of entity ids to query for running the projection.</returns>
+    Task<Id[]> GetEntityIds(Id projectionId, TProjection projectionSnapshot);
+
+    /// <summary>
+    ///     Map an entity id to a set of projection ids.
+    /// </summary>
+    /// <param name="entityId">The id of th entity.</param>
+    /// <returns>The set of projection ids to query for running the projection.</returns>
+    Task<Id[]> GetProjectionIds(Id entityId);
+}

src/EntityDb.Common/Annotations/EntityAnnotation.cs

@@ -1,4 +1,6 @@
 using EntityDb.Abstractions.Annotations;
+using EntityDb.Abstractions.Transactions;
+using EntityDb.Abstractions.Transactions.Steps;
 using EntityDb.Abstractions.ValueObjects;
 
 namespace EntityDb.Common.Annotations;
@@ -10,4 +12,18 @@ internal record EntityAnnotation<TData>
     Id EntityId,
     VersionNumber EntityVersionNumber,
     TData Data
-) : IEntityAnnotation<TData>;
+) : IEntityAnnotation<TData>
+{
+    public static EntityAnnotation<TData> CreateFrom(ITransaction transaction, ITransactionStep transactionStep,
+        TData data)
+    {
+        return new
+        (
+            transaction.Id,
+            transaction.TimeStamp,
+            transactionStep.EntityId,
+            transactionStep.EntityVersionNumber,
+            data
+        );
+    }
+}

src/EntityDb.Common/Disposables/DisposableResourceBaseClass.cs

@@ -1,10 +1,12 @@
 using EntityDb.Abstractions.Disposables;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading.Tasks;
 
 namespace EntityDb.Common.Disposables;
 
 internal class DisposableResourceBaseClass : IDisposableResource
 {
+    [ExcludeFromCodeCoverage(Justification = "All Tests Use DisposeAsync")]
     public virtual void Dispose()
     {
         DisposeAsync().AsTask().Wait();

src/EntityDb.Common/Disposables/DisposableResourceBaseRecord.cs

@@ -1,10 +1,12 @@
 using EntityDb.Abstractions.Disposables;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading.Tasks;
 
 namespace EntityDb.Common.Disposables;
 
 internal record DisposableResourceBaseRecord : IDisposableResource
 {
+    [ExcludeFromCodeCoverage(Justification = "All Tests Use DisposeAsync")]
     public virtual void Dispose()
     {
         DisposeAsync().AsTask().Wait();

src/EntityDb.Common/Entities/IEntity.cs

@@ -15,10 +15,16 @@ public interface IEntity<out TEntity>
     /// <returns>A new instance of <typeparamref name="TEntity" />.</returns>
     abstract static TEntity Construct(Id entityId);
 
+    /// <summary>
+    ///     Returns the id of the entity.
+    /// </summary>
+    /// <returns>The id of this entity.</returns>
+    Id GetId();
+
     /// <summary>
     ///     Returns the version number of the entity.
     /// </summary>
-    /// <returns></returns>
+    /// <returns>The id of this entity.</returns>
     VersionNumber GetVersionNumber();
 
     /// <summary>

src/EntityDb.Common/Extensions/ServiceCollectionExtensions.cs

@@ -1,7 +1,9 @@
 using EntityDb.Abstractions.Agents;
 using EntityDb.Abstractions.Entities;
+using EntityDb.Abstractions.Projections;
 using EntityDb.Abstractions.Transactions;
 using EntityDb.Common.Entities;
+using EntityDb.Common.Projections;
 using EntityDb.Common.Snapshots;
 using EntityDb.Common.Transactions;
 using EntityDb.Common.Transactions.Builders;
@@ -85,16 +87,49 @@ public static void AddEntity<TEntity>(this IServiceCollection serviceCollection)
     /// <summary>
     ///     Adds a transaction subscriber that records snapshots of entities.
     /// </summary>
-    /// <typeparam name="TSnapshot">The type of the snapshot.</typeparam>
     /// <param name="serviceCollection">The service collection.</param>
     /// <param name="snapshotSessionOptionsName">The agent's intent for the snapshot repository.</param>
     /// <param name="synchronousMode">If <c>true</c> then snapshots will be synchronously recorded.</param>
-    public static void AddEntitySnapshotTransactionSubscriber<TSnapshot>(this IServiceCollection serviceCollection,
+    /// <typeparam name="TEntity">The type of the entity.</typeparam>
+    public static void AddEntitySnapshotTransactionSubscriber<TEntity>(this IServiceCollection serviceCollection,
+        string snapshotSessionOptionsName, bool synchronousMode = false)
+        where TEntity : IEntity<TEntity>, ISnapshot<TEntity>
+    {
+        serviceCollection.AddSingleton<ITransactionSubscriber>(serviceProvider =>
+            EntitySnapshotTransactionSubscriber<TEntity>.Create(serviceProvider, snapshotSessionOptionsName,
+                synchronousMode));
+    }
+
+    /// <summary>
+    ///     Adds a projection strategy.
+    /// </summary>
+    /// <param name="serviceCollection">The service collection.</param>
+    /// <typeparam name="TProjection">The type of the projection.</typeparam>
+    /// <typeparam name="TProjectionStrategy">The type of the projection strategy.</typeparam>
+    public static void AddProjection<TProjection, TProjectionStrategy>(
+        this IServiceCollection serviceCollection)
+        where TProjection : IProjection<TProjection>
+        where TProjectionStrategy : class, IProjectionStrategy<TProjection>
+    {
+        serviceCollection.AddSingleton<IProjectionStrategy<TProjection>, TProjectionStrategy>();
+        serviceCollection
+            .AddTransient<IProjectionRepositoryFactory<TProjection>, ProjectionRepositoryFactory<TProjection>>();
+    }
+
+    /// <summary>
+    ///     Adds a transaction subscriber that records snapshots of projections.
+    /// </summary>
+    /// <param name="serviceCollection">The service collection.</param>
+    /// <param name="snapshotSessionOptionsName">The agent's intent for the snapshot repository.</param>
+    /// <param name="synchronousMode">If <c>true</c> then snapshots will be synchronously recorded.</param>
+    /// <typeparam name="TProjection">The type of the projection.</typeparam>
+    public static void AddProjectionSnapshotTransactionSubscriber<TProjection>(
+        this IServiceCollection serviceCollection,
         string snapshotSessionOptionsName, bool synchronousMode = false)
-        where TSnapshot : ISnapshot<TSnapshot>
+        where TProjection : IProjection<TProjection>, ISnapshot<TProjection>
     {
         serviceCollection.AddSingleton<ITransactionSubscriber>(serviceProvider =>
-            EntitySnapshotTransactionSubscriber<TSnapshot>.Create(serviceProvider, snapshotSessionOptionsName,
+            ProjectionSnapshotTransactionSubscriber<TProjection>.Create(serviceProvider, snapshotSessionOptionsName,
                 synchronousMode));
     }
 }

src/EntityDb.Common/Projections/IProjection.cs

@@ -0,0 +1,31 @@
+using EntityDb.Abstractions.Annotations;
+using EntityDb.Abstractions.ValueObjects;
+
+namespace EntityDb.Common.Projections;
+
+/// <summary>
+///     Provides basic functionality for the common implementations.
+/// </summary>
+/// <typeparam name="TProjection"></typeparam>
+public interface IProjection<out TProjection>
+{
+    /// <summary>
+    ///     Creates a new instance of a <typeparamref name="TProjection" />.
+    /// </summary>
+    /// <param name="projectionId">The id of the entity.</param>
+    /// <returns>A new instance of <typeparamref name="TProjection" />.</returns>
+    abstract static TProjection Construct(Id projectionId);
+
+    /// <summary>
+    ///     Returns the current version number of an entity.
+    /// </summary>
+    /// <returns></returns>
+    VersionNumber GetEntityVersionNumber(Id entityId);
+
+    /// <summary>
+    ///     Returns a new <typeparamref name="TProjection"/> that incorporates the commands for a particular entity id.
+    /// </summary>
+    /// <param name="annotatedCommands">The annotated commands.</param>
+    /// <returns>A new <typeparamref name="TProjection"/> that incorporates <paramref name="annotatedCommands"/>.</returns>
+    TProjection Reduce(params IEntityAnnotation<object>[] annotatedCommands);
+}

src/EntityDb.Common/Projections/ProjectionRepository.cs

@@ -0,0 +1,67 @@
+using EntityDb.Abstractions.Projections;
+using EntityDb.Abstractions.Snapshots;
+using EntityDb.Abstractions.Transactions;
+using EntityDb.Abstractions.ValueObjects;
+using EntityDb.Common.Disposables;
+using EntityDb.Common.Queries;
+using Microsoft.Extensions.DependencyInjection;
+using System;
+using System.Threading.Tasks;
+
+namespace EntityDb.Common.Projections;
+
+internal sealed class ProjectionRepository<TProjection> : DisposableResourceBaseClass, IProjectionRepository<TProjection>
+    where TProjection : IProjection<TProjection>
+{
+    public IProjectionStrategy<TProjection> ProjectionStrategy { get; }
+    public ITransactionRepository TransactionRepository { get; }
+    public ISnapshotRepository<TProjection> SnapshotRepository { get; }
+
+    public ProjectionRepository
+    (
+        IProjectionStrategy<TProjection> projectionStrategy,
+        ISnapshotRepository<TProjection> snapshotRepository,
+        ITransactionRepository transactionRepository
+    )
+    {
+        ProjectionStrategy = projectionStrategy;
+        TransactionRepository = transactionRepository;
+        SnapshotRepository = snapshotRepository;
+    }
+
+    public async Task<TProjection> GetCurrent(Id projectionId)
+    {
+        var projection = await SnapshotRepository.GetSnapshot(projectionId) ?? TProjection.Construct(projectionId);
+
+        var entityIds = await ProjectionStrategy.GetEntityIds(projectionId, projection);
+
+        if (entityIds.Length == 0)
+        {
+            return projection;
+        }
+
+        foreach (var entityId in entityIds)
+        {
+            var entityVersionNumber = projection.GetEntityVersionNumber(entityId);
+
+            var commandQuery = new GetCurrentEntityQuery(entityId, entityVersionNumber);
+
+            var annotatedCommands = await TransactionRepository.GetAnnotatedCommands(commandQuery);
+
+            projection = projection.Reduce(annotatedCommands);
+        }
+
+        return projection;
+    }
+
+    public static ProjectionRepository<TProjection> Create
+    (
+        IServiceProvider serviceProvider,
+        ITransactionRepository transactionRepository,
+        ISnapshotRepository<TProjection> snapshotRepository
+    )
+    {
+        return ActivatorUtilities.CreateInstance<ProjectionRepository<TProjection>>(serviceProvider,
+            transactionRepository, snapshotRepository);
+    }
+}

src/EntityDb.Common/Projections/ProjectionRepositoryFactory.cs

@@ -0,0 +1,39 @@
+using EntityDb.Abstractions.Projections;
+using EntityDb.Abstractions.Snapshots;
+using EntityDb.Abstractions.Transactions;
+using System;
+using System.Threading.Tasks;
+
+namespace EntityDb.Common.Projections;
+
+internal class ProjectionRepositoryFactory<TProjection> : IProjectionRepositoryFactory<TProjection>
+    where TProjection : IProjection<TProjection>
+{
+    private readonly IServiceProvider _serviceProvider;
+    private readonly ITransactionRepositoryFactory _transactionRepositoryFactory;
+    private readonly ISnapshotRepositoryFactory<TProjection> _snapshotRepositoryFactory;
+
+    public ProjectionRepositoryFactory
+    (
+        IServiceProvider serviceProvider,
+        ITransactionRepositoryFactory transactionRepositoryFactory,
+        ISnapshotRepositoryFactory<TProjection> snapshotRepositoryFactory
+    )
+    {
+        _serviceProvider = serviceProvider;
+        _transactionRepositoryFactory = transactionRepositoryFactory;
+        _snapshotRepositoryFactory = snapshotRepositoryFactory;
+    }
+
+    public async Task<IProjectionRepository<TProjection>> CreateRepository(string transactionSessionOptionsName, string snapshotSessionOptionsName)
+    {
+        var transactionRepository =
+            await _transactionRepositoryFactory.CreateRepository(transactionSessionOptionsName);
+
+        var snapshotRepository =
+            await _snapshotRepositoryFactory.CreateRepository(snapshotSessionOptionsName);
+
+        return ProjectionRepository<TProjection>.Create(_serviceProvider,
+            transactionRepository, snapshotRepository);
+    }
+}