Time-keyed projections (#239)

* Enable property & eventsource to be used with occurred in projections, allowing useful aggregations.
Also added support for specifying a function to create the key directly, with even more flexibility.

* Projection Key by function via KeyFromFunctionAttribute

Source/Projections/Builder/KeySelectorBuilder.cs

@@ -14,13 +14,13 @@ public class KeySelectorBuilder
     /// Select projection key from the <see cref="EventSourceId"/>.
     /// </summary>
     /// <returns>A <see cref="KeySelector"/>.</returns>
-    public static KeySelector KeyFromEventSource() => KeySelector.EventSource;
+    public static KeySelector KeyFromEventSource => KeySelector.EventSource;
 
     /// <summary>
     /// Select projection key from the <see cref="PartitionId"/>.
     /// </summary>
     /// <returns>A <see cref="KeySelector"/>.</returns>
-    public static KeySelector KeyFromPartitionId() => KeySelector.Partition;
+    public static KeySelector KeyFromPartitionId => KeySelector.Partition;
 
     /// <summary>
     /// Select projection key from a property of the event.
@@ -46,4 +46,21 @@ public static KeySelector StaticKey(Key staticKey)
     /// <returns>A <see cref="KeySelector"/>.</returns>
     public static KeySelector KeyFromEventOccurred(OccurredFormat occurredFormat)
         => KeySelector.Occurred(occurredFormat);
+
+    /// <summary>
+    /// Select projection key from a property of the event.
+    /// </summary>
+    /// <param name="selectorExpression">The property on the event.</param>
+    /// <param name="occurredFormat">The date time format.</param>
+    /// <returns>A <see cref="KeySelector"/>.</returns>
+    public static KeySelector KeyFromPropertyAndEventOccurred(KeySelectorExpression selectorExpression, OccurredFormat occurredFormat)
+        => KeySelector.PropertyAndOccured(selectorExpression, occurredFormat);
+
+    /// <summary>
+    /// Select projection key from when an event occurred.
+    /// </summary>
+    /// <param name="occurredFormat">The date time format.</param>
+    /// <returns>A <see cref="KeySelector"/>.</returns>
+    public static KeySelector KeyFromEventSourceIdAndOccurred(OccurredFormat occurredFormat)
+        => KeySelector.EventSourceAndOccured(occurredFormat);
 }

Source/Projections/Builder/KeySelectorBuilder{TEvent}.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Linq.Expressions;
+using Dolittle.SDK.Events;
 
 namespace Dolittle.SDK.Projections.Builder;
 
@@ -29,4 +30,18 @@ public KeySelector KeyFromProperty<TProperty>(Expression<Func<TEvent, TProperty>
 
         throw new KeySelectorExpressionWasNotAMemberExpression();
     }
+
+    /// <summary>
+    /// Select projection key from a property of the event.
+    /// </summary>
+    /// <typeparam name="TProperty">The property type.</typeparam>
+    /// <param name="function">The function for getting the projection key (id).</param>
+    /// <returns>A <see cref="KeySelector"/>.</returns>
+    /// <exception cref="KeySelectorExpressionWasNotAMemberExpression">Is thrown when the provided property expression is not a member expression.</exception>
+    public KeySelector KeyFromFunction(Func<TEvent, EventContext, Key> function)
+    {
+        if (function is null) throw new ArgumentNullException(nameof(function));
+
+        return KeySelector.ByFunction(function);
+    }
 }

Source/Projections/IKeySelector.cs

@@ -0,0 +1,22 @@
+// Copyright (c) Dolittle. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using Dolittle.SDK.Events;
+
+namespace Dolittle.SDK.Projections;
+
+/// <summary>
+/// Use this interface to define projection key selectors.
+/// Instances of this interface MUST be thread safe and stateless, as they are used as singletons.
+/// </summary>
+/// <typeparam name="TEvent">The mapped event type</typeparam>
+public interface IKeySelector<TEvent> where TEvent : class
+{
+    /// <summary>
+    /// Map to a <see cref="Key"/> from an event and context.
+    /// </summary>
+    /// <param name="event"></param>
+    /// <param name="eventContext"></param>
+    /// <returns>The projection key</returns>
+    Key Selector(TEvent @event, EventContext eventContext);
+}

Source/Projections/Internal/ProjectionsProcessor.cs

@@ -103,28 +103,4 @@ protected override RetryProcessingState GetRetryProcessingStateFromRequest(Handl
     /// <inheritdoc/>
     protected override EventHandlerResponse CreateResponseFromFailure(ProcessorFailure failure)
         => new() { Failure = failure };
-
-    static ProjectionEventSelector CreateProjectionEventSelector(EventSelector eventSelector)
-    {
-        static ProjectionEventSelector WithEventType(EventSelector eventSelector, Action<ProjectionEventSelector> callback)
-        {
-            var message = new ProjectionEventSelector();
-            callback(message);
-            message.EventType = eventSelector.EventType.ToProtobuf();
-            return message;
-        }
-
-        return eventSelector.KeySelector.Type switch
-        {
-            KeySelectorType.EventSourceId => WithEventType(eventSelector, _ => _.EventSourceKeySelector = new EventSourceIdKeySelector()),
-            KeySelectorType.PartitionId => WithEventType(eventSelector, _ => _.PartitionKeySelector = new PartitionIdKeySelector()),
-            KeySelectorType.Property => WithEventType(eventSelector,
-                _ => _.EventPropertyKeySelector = new EventPropertyKeySelector { PropertyName = eventSelector.KeySelector.Expression ?? string.Empty }),
-            KeySelectorType.Static => WithEventType(eventSelector,
-                _ => _.StaticKeySelector = new StaticKeySelector { StaticKey = eventSelector.KeySelector.StaticKey ?? string.Empty }),
-            KeySelectorType.EventOccurred => WithEventType(eventSelector,
-                _ => _.EventOccurredKeySelector = new EventOccurredKeySelector { Format = eventSelector.KeySelector.OccurredFormat ?? string.Empty }),
-            _ => throw new UnknownKeySelectorType(eventSelector.KeySelector.Type)
-        };
-    }
 }

Source/Projections/KeyFromEventOccurredAttribute.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
-using Dolittle.SDK.Projections.Builder;
 
 namespace Dolittle.SDK.Projections;
 
@@ -15,7 +14,7 @@ public class KeyFromEventOccurredAttribute : Attribute, IKeySelectorAttribute
     /// <summary>
     /// Initializes a new instance of the <see cref="KeyFromEventOccurredAttribute"/> class.
     /// </summary>
-    /// <param name="occurredFormat">The name of the property.</param>
+    /// <param name="occurredFormat">The date time format.</param>
     public KeyFromEventOccurredAttribute(string occurredFormat) => OccurredFormat = occurredFormat;
 
     /// <summary>
@@ -24,5 +23,5 @@ public class KeyFromEventOccurredAttribute : Attribute, IKeySelectorAttribute
     public OccurredFormat OccurredFormat { get; }
 
     /// <inheritdoc/>
-    public KeySelector KeySelector => KeySelectorBuilder.KeyFromEventOccurred(OccurredFormat);
+    public KeySelector KeySelector => KeySelector.Occurred(OccurredFormat);
 }

Source/Projections/KeyFromEventSourceAndOccurredAttribute.cs

@@ -0,0 +1,31 @@
+// Copyright (c) Dolittle. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+
+namespace Dolittle.SDK.Projections;
+
+/// <summary>
+/// Decorates a projection method with the <see cref="KeySelectorType.Property" />.
+/// </summary>
+[AttributeUsage(AttributeTargets.Method)]
+public class KeyFromEventSourceAndOccurredAttribute : Attribute, IKeySelectorAttribute
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="KeyFromEventSourceAndOccurredAttribute"/> class.
+    /// </summary>
+    /// <param name="propertyName">The name of the property.</param>
+    /// <param name="occurredFormat">The date time format.</param>
+    public KeyFromEventSourceAndOccurredAttribute(string occurredFormat)
+    {
+        OccurredFormat = occurredFormat;
+    }
+
+    /// <summary>
+    /// Gets the <see cref="OccurredFormat" />.
+    /// </summary>
+    public OccurredFormat OccurredFormat { get; }
+
+    /// <inheritdoc/>
+    public KeySelector KeySelector => KeySelector.EventSourceAndOccured(OccurredFormat);
+}

Source/Projections/KeyFromEventSourceAttribute.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
-using Dolittle.SDK.Projections.Builder;
 
 namespace Dolittle.SDK.Projections;
 
@@ -13,5 +12,5 @@ namespace Dolittle.SDK.Projections;
 public class KeyFromEventSourceAttribute : Attribute, IKeySelectorAttribute
 {
     /// <inheritdoc/>
-    public KeySelector KeySelector { get; } = KeySelectorBuilder.KeyFromEventSource();
-}
+    public KeySelector KeySelector => KeySelector.EventSource;
+}

Source/Projections/KeyFromFunctionAttribute.cs

@@ -0,0 +1,23 @@
+// Copyright (c) Dolittle. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+
+namespace Dolittle.SDK.Projections;
+
+static class KeySelectorInstance<TKeySelector, TEvent> where TKeySelector : IKeySelector<TEvent>, new() where TEvent : class
+{
+    public static TKeySelector Mapper { get; } = new();
+    public static KeySelector Instance { get; } = KeySelector.ByFunction<TEvent>(Mapper.Selector);
+}
+
+/// <summary>
+/// Decorates a projection method with the <see cref="KeySelectorType.Function" />.
+/// </summary>
+[AttributeUsage(AttributeTargets.Method)]
+public class KeyFromFunctionAttribute<TKeySelector, TEvent> : Attribute, IKeySelectorAttribute
+    where TKeySelector : IKeySelector<TEvent>, new() where TEvent : class
+{
+    /// <inheritdoc/>
+    public KeySelector KeySelector => KeySelectorInstance<TKeySelector, TEvent>.Instance;
+}

Source/Projections/KeyFromPartitionAttribute.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
-using Dolittle.SDK.Projections.Builder;
 
 namespace Dolittle.SDK.Projections;
 
@@ -13,5 +12,5 @@ namespace Dolittle.SDK.Projections;
 public class KeyFromPartitionAttribute : Attribute, IKeySelectorAttribute
 {
     /// <inheritdoc/>
-    public KeySelector KeySelector { get; } = KeySelectorBuilder.KeyFromPartitionId();
-}
+    public KeySelector KeySelector => KeySelector.Partition;
+}

Source/Projections/KeyFromPropertyAndOccurredAttribute.cs

@@ -0,0 +1,37 @@
+// Copyright (c) Dolittle. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+
+namespace Dolittle.SDK.Projections;
+
+/// <summary>
+/// Decorates a projection method with the <see cref="KeySelectorType.Property" />.
+/// </summary>
+[AttributeUsage(AttributeTargets.Method)]
+public class KeyFromPropertyAndOccurredAttribute : Attribute, IKeySelectorAttribute
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="KeyFromPropertyAttribute"/> class.
+    /// </summary>
+    /// <param name="propertyName">The name of the property.</param>
+    /// <param name="occurredFormat">The date time format.</param>
+    public KeyFromPropertyAndOccurredAttribute(string propertyName, string occurredFormat)
+    {
+        Expression = propertyName;
+        OccurredFormat = occurredFormat;
+    }
+
+    /// <summary>
+    /// Gets the <see cref="KeySelector" />.
+    /// </summary>
+    public KeySelectorExpression Expression { get; }
+
+    /// <summary>
+    /// Gets the <see cref="OccurredFormat" />.
+    /// </summary>
+    public OccurredFormat OccurredFormat { get; }
+
+    /// <inheritdoc/>
+    public KeySelector KeySelector => KeySelector.PropertyAndOccured(Expression, OccurredFormat);
+}

Source/Projections/KeyFromPropertyAttribute.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
-using Dolittle.SDK.Projections.Builder;
 
 namespace Dolittle.SDK.Projections;
 
@@ -24,5 +23,5 @@ public class KeyFromPropertyAttribute : Attribute, IKeySelectorAttribute
     public KeySelectorExpression Expression { get; }
 
     /// <inheritdoc/>
-    public KeySelector KeySelector => KeySelectorBuilder.KeyFromProperty(Expression);
+    public KeySelector KeySelector => KeySelector.Property(Expression);
 }

Source/Projections/KeySelector.cs

@@ -12,46 +12,71 @@ namespace Dolittle.SDK.Projections;
 /// </summary>
 public class KeySelector
 {
-    KeySelector(KeySelectorType type, KeySelectorExpression expression, Key staticKey, OccurredFormat occurredFormat)
+    KeySelector(KeySelectorType type, KeySelectorExpression expression, Key staticKey, OccurredFormat occurredFormat, Func<object, EventContext, Key>? function)
     {
         Type = type;
         Expression = expression;
         StaticKey = staticKey;
         OccurredFormat = occurredFormat;
+        Function = function;
     }
 
+    public Func<object, EventContext, Key>? Function { get; }
+
     /// <summary>
     /// Creates a <see cref="KeySelectorType.PartitionId"/> <see cref="KeySelector"/>.
     /// </summary>
     /// <returns>The <see cref="KeySelector"/>.</returns>
-    public static KeySelector Partition { get; } = new(KeySelectorType.PartitionId, "", "", "");
+    public static KeySelector Partition { get; } = new(KeySelectorType.PartitionId, "", "", "", null);
 
     /// <summary>
     /// Creates a <see cref="KeySelectorType.EventSourceId"/> <see cref="KeySelector"/>.
     /// </summary>
     /// <returns>The <see cref="KeySelector"/>.</returns>
-    public static KeySelector EventSource { get; } = new(KeySelectorType.EventSourceId, "", "", "");
+    public static KeySelector EventSource { get; } = new(KeySelectorType.EventSourceId, "", "", "", null);
+
+    public static KeySelector ByFunction<TEvent>(Func<TEvent, EventContext, Key> function) where TEvent : class
+    {
+        return new KeySelector(KeySelectorType.Function, "", "", "", (evt, eventContext) => function((TEvent)evt, eventContext));
+    }
 
     /// <summary>
     /// Creates a <see cref="KeySelectorType.Property"/> <see cref="KeySelector"/>.
     /// </summary>
     /// <param name="expression">The <see cref="KeySelectorExpression"/>.</param>
     /// <returns>The <see cref="KeySelector"/>.</returns>
-    public static KeySelector Property(KeySelectorExpression expression) => new(KeySelectorType.Property, expression, "", "");
+    public static KeySelector Property(KeySelectorExpression expression) => new(KeySelectorType.Property, expression, "", "", null);
 
     /// <summary>
     /// Creates a <see cref="KeySelectorType.Property"/> <see cref="KeySelector"/>.
     /// </summary>
     /// <param name="key">The static <see cref="Key"/>.</param>
     /// <returns>The <see cref="KeySelector"/>.</returns>
-    public static KeySelector Static(Key key) => new(KeySelectorType.Static, "", key, "");
+    public static KeySelector Static(Key key) => new(KeySelectorType.Static, "", key, "", null);
 
     /// <summary>
-    /// Creates a <see cref="KeySelectorType.Property"/> <see cref="KeySelector"/>.
+    /// Creates a <see cref="KeySelectorType.EventOccurred"/> <see cref="KeySelector"/>.
+    /// </summary>
+    /// <param name="occurredFormat">The <see cref="OccurredFormat"/>.</param>
+    /// <returns>The <see cref="KeySelector"/>.</returns>
+    public static KeySelector Occurred(OccurredFormat occurredFormat) => new(KeySelectorType.EventOccurred, "", "", occurredFormat, null);
+
+    /// <summary>
+    /// Creates a <see cref="KeySelectorType.PropertyAndEventOccurred"/> <see cref="KeySelector"/>.
     /// </summary>
+    /// <param name="expression">The <see cref="KeySelectorExpression"/>.</param>
     /// <param name="occurredFormat">The <see cref="OccurredFormat"/>.</param>
     /// <returns>The <see cref="KeySelector"/>.</returns>
-    public static KeySelector Occurred(OccurredFormat occurredFormat) => new(KeySelectorType.EventOccurred, "", "", occurredFormat);
+    public static KeySelector PropertyAndOccured(KeySelectorExpression expression, OccurredFormat occurredFormat) =>
+        new(KeySelectorType.PropertyAndEventOccurred, expression, "", occurredFormat, null);
+
+    /// <summary>
+    /// Creates a <see cref="KeySelectorType.EventSourceIdAndOccurred"/> <see cref="KeySelector"/>.
+    /// </summary>
+    /// <param name="occurredFormat">The <see cref="OccurredFormat"/>.</param>
+    /// <returns>The <see cref="KeySelector"/>.</returns>
+    public static KeySelector EventSourceAndOccured(OccurredFormat occurredFormat) =>
+        new(KeySelectorType.EventSourceIdAndOccurred, "", "", occurredFormat, null);
 
     /// <summary>
     /// Gets the <see cref="KeySelectorType" />.
@@ -73,18 +98,21 @@ public class KeySelector
     /// </summary>
     public OccurredFormat OccurredFormat { get; }
 
-    public Key GetKey(object evt, EventContext eventContext)
-    {
-        return Type switch
+    public Key GetKey(object evt, EventContext eventContext) =>
+        Type switch
         {
             KeySelectorType.PartitionId => eventContext.EventSourceId.Value,
             KeySelectorType.EventSourceId => eventContext.EventSourceId.Value,
             KeySelectorType.Static => StaticKey,
             KeySelectorType.EventOccurred => eventContext.Occurred.ToString(OccurredFormat.Value, CultureInfo.InvariantCulture),
             KeySelectorType.Property => GetProperty(evt, Expression),
+            KeySelectorType.Function => Function!.Invoke(evt, eventContext),
+            KeySelectorType.EventSourceIdAndOccurred =>
+                $"{eventContext.EventSourceId.Value}_{eventContext.Occurred.ToString(OccurredFormat.Value, CultureInfo.InvariantCulture)}",
+            KeySelectorType.PropertyAndEventOccurred =>
+                $"{GetProperty(evt, Expression)}_{eventContext.Occurred.ToString(OccurredFormat.Value, CultureInfo.InvariantCulture)}",
             _ => eventContext.EventSourceId.Value
         };
-    }
 
     static string GetProperty(object evt, KeySelectorExpression expression)
     {