Support Timestamp property in POCO entities

It's sometimes useful to be able to read the Timestamp value managed by Table Storage, so we just allow POCOs to be able to read it by just declaring a property with that name.

Fixes #60

Author: kzu

readme.md

@@ -185,6 +185,9 @@ var repo = TableRepository.Create<Product>(...,
 > NOTE: when using alternative serializers, entities might need to be annotated with whatever 
 > attributes are required by the underlying libraries.
 
+> NOTE: if access to the `Timestamp` managed by Table Storage for the entity is needed, just declare a property 
+> with that name with either `DateTimeOffset`, `DateTime` or `string` type.
+
 ### Attributes
 
 If you want to avoid using strings with the factory methods, you can also annotate the 

src/TableStorage/TableRepository`1.cs

@@ -192,6 +192,8 @@ T ToEntity(DynamicTableEntity entity)
             if (rowKeyProperty != null)
                 writer.WriteString(rowKeyProperty, entity.RowKey);
 
+            writer.WriteString(nameof(ITableEntity.Timestamp), entity.Timestamp);
+
             foreach (var property in entity.Properties)
             {
                 switch (property.Value.PropertyType)

src/Tests/RepositoryTests.cs

@@ -159,6 +159,35 @@ public void CanSpecifyRowKeyLambda()
             TablePartition.Create<EntityNoRowKey>(CloudStorageAccount.DevelopmentStorageAccount, e => e.Id ?? "");
         }
 
+        [Fact]
+        public async Task CanReadTimestamp()
+        {
+            await TablePartition
+                .Create<TimestampedEntity>(
+                    CloudStorageAccount.DevelopmentStorageAccount,
+                    "Timestamped", "Timestamped", e => e.ID)
+                .PutAsync(
+                    new TimestampedEntity("Foo"));
+
+            Assert.NotNull((await TablePartition
+                .Create<TimestampedEntity>(
+                    CloudStorageAccount.DevelopmentStorageAccount,
+                    "Timestamped", "Timestamped", e => e.ID)
+                .GetAsync("Foo"))!.Timestamp);
+
+            Assert.NotNull((await TablePartition
+                .Create<StringTimestampedEntity>(
+                    CloudStorageAccount.DevelopmentStorageAccount,
+                    "Timestamped", "Timestamped", e => e.ID)
+                .GetAsync("Foo"))!.Timestamp);
+
+            Assert.NotNull((await TablePartition
+                .Create<TimestampedDateTimeEntity>(
+                    CloudStorageAccount.DevelopmentStorageAccount,
+                    "Timestamped", "Timestamped", e => e.ID)
+                .GetAsync("Foo"))!.Timestamp);
+        }
+
         [Fact]
         public void DefaultTableNameUsesAttribute()
         {
@@ -385,5 +414,20 @@ record AttributedRecordEntity([PartitionKey] string Kind, [RowKey] string ID)
             public string? Status { get; set; }
             public string? Reason { get; set; }
         }
+
+        record TimestampedEntity(string ID)
+        {
+            public DateTimeOffset? Timestamp { get; set; }
+        }
+
+        record StringTimestampedEntity(string ID)
+        {
+            public string? Timestamp { get; set; }
+        }
+
+        record TimestampedDateTimeEntity(string ID)
+        {
+            public DateTime? Timestamp { get; set; }
+        }
     }
 }