feature: get at version

allows you to request the entity at a specific version

Author: the-avid-engineer

src/EntityDb.Abstractions/Entities/IEntityRepository.cs

@@ -24,6 +24,14 @@ public interface IEntityRepository<TEntity> : IDisposable, IAsyncDisposable
         /// <returns>The current state of a <typeparamref name="TEntity" /> or constructs a new <typeparamref name="TEntity" />.</returns>
         Task<TEntity> GetCurrent(Guid entityId);
 
+        /// <summary>
+        ///     Returns a previous state of <typeparamref name="TEntity" />.
+        /// </summary>
+        /// <param name="entityId">The id of the entity.</param>
+        /// <param name="lteVersionNumber">The version of the entity to fetch.</param>
+        /// <returns>A previous state of <typeparamref name="TEntity" />.</returns>
+        Task<TEntity> GetAtVersion(Guid entityId, ulong lteVersionNumber);
+
         /// <summary>
         ///     Inserts a single transaction with an atomic commit.
         /// </summary>

src/EntityDb.Common/Entities/EntityRepository.cs

@@ -83,6 +83,17 @@ public async Task<TEntity> GetCurrent(Guid entityId)
             return entity;
         }
 
+        public async Task<TEntity> GetAtVersion(Guid entityId, ulong lteVersionNumber)
+        {
+            var commandQuery = new GetEntityAtVersionQuery(entityId, lteVersionNumber);
+
+            var commands = await _transactionRepository.GetCommands(commandQuery);
+
+            return _constructingStrategy
+                .Construct(entityId)
+                .Reduce(commands);
+        }
+
         public async Task<bool> PutTransaction(ITransaction<TEntity> transaction)
         {
             var success = await _transactionRepository.PutTransaction(transaction);

src/EntityDb.Common/Queries/GetEntityAtVersionQuery.cs

@@ -0,0 +1,31 @@
+using EntityDb.Abstractions.Queries;
+using EntityDb.Abstractions.Queries.FilterBuilders;
+using EntityDb.Abstractions.Queries.SortBuilders;
+using System;
+
+namespace EntityDb.Common.Queries
+{
+    internal sealed record GetEntityAtVersionQuery(Guid EntityId, ulong LteVersionNumber) : ICommandQuery
+    {
+        public TFilter GetFilter<TFilter>(ICommandFilterBuilder<TFilter> builder)
+        {
+            return builder.And
+            (
+                builder.EntityIdIn(EntityId),
+                builder.EntityVersionNumberLte(LteVersionNumber)
+            );
+        }
+
+        public TSort GetSort<TSort>(ICommandSortBuilder<TSort> builder)
+        {
+            return builder.Combine
+            (
+                builder.EntityVersionNumber(true)
+            );
+        }
+
+        public int? Skip => null;
+
+        public int? Take => null;
+    }
+}