implement DynamoDBAutoGeneratedTimestampAttribute

generator/.DevConfigs/c952ab1e-3056-4598-9d0e-f7f02187e982.json

@@ -0,0 +1,11 @@
+{
+  "services": [
+    {
+      "serviceName": "DynamoDBv2",
+      "type": "minor",
+      "changeLogMessages": [
+        "Add support for DynamoDBAutoGeneratedTimestampAttribute that sets current timestamp during persistence operations."
+      ]
+    }
+  ]
+}

sdk/src/Services/DynamoDBv2/Custom/DataModel/Attributes.cs

@@ -688,4 +688,49 @@ public DynamoDBLocalSecondaryIndexRangeKeyAttribute(params string[] indexNames)
             IndexNames = indexNames.Distinct(StringComparer.Ordinal).ToArray();
         }
     }
+
+    /// <summary>
+    /// Specifies that the decorated property or field should have its value automatically
+    /// set to the current timestamp during persistence operations.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, Inherited = true, AllowMultiple = false)]
+    public sealed class DynamoDBAutoGeneratedTimestampAttribute : DynamoDBPropertyAttribute
+    {
+
+        /// <summary>
+        /// Default constructor. Timestamp is set on both create and update.
+        /// </summary>
+        public DynamoDBAutoGeneratedTimestampAttribute()
+            : base()
+        {
+        }
+
+
+        /// <summary>
+        /// Constructor that specifies an alternate attribute name.
+        /// </summary>
+        /// <param name="attributeName">Name of attribute to be associated with property or field.</param>
+        public DynamoDBAutoGeneratedTimestampAttribute(string attributeName)
+            : base(attributeName)
+        {
+        }
+        /// <summary>
+        /// Constructor that specifies a custom converter.
+        /// </summary>
+        /// <param name="converter">Custom converter type.</param>
+        public DynamoDBAutoGeneratedTimestampAttribute([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.Interfaces)] Type converter)
+            : base(converter)
+        {
+        }
+
+        /// <summary>
+        /// Constructor that specifies an alternate attribute name and a custom converter.
+        /// </summary>
+        /// <param name="attributeName">Name of attribute to be associated with property or field.</param>
+        /// <param name="converter">Custom converter type.</param>
+        public DynamoDBAutoGeneratedTimestampAttribute(string attributeName, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.Interfaces)] Type converter)
+            : base(attributeName, converter)
+        {
+        }
+    }
 }

sdk/src/Services/DynamoDBv2/Custom/DataModel/Context.cs

@@ -457,7 +457,7 @@ private async Task SaveHelperAsync([DynamicallyAccessedMembers(InternalConstants
                     .ConfigureAwait(false);
             }
 
-            if (counterConditionExpression == null && versionExpression == null) return;
+            if (counterConditionExpression == null && versionExpression == null && !storage.Config.HasAutogeneratedProperties) return;
 
             if (returnValues == ReturnValues.AllNewAttributes)
             {

sdk/src/Services/DynamoDBv2/Custom/DataModel/ContextInternal.cs

@@ -27,6 +27,7 @@
 using System.Globalization;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq.Expressions;
+using Amazon.Util;
 using ThirdParty.RuntimeBackports;
 using Expression = System.Linq.Expressions.Expression;
 
@@ -139,7 +140,16 @@ private static PropertyStorage[] GetCounterProperties(ItemStorage storage)
         {
             var counterProperties = storage.Config.BaseTypeStorageConfig.Properties.
                 Where(propertyStorage => propertyStorage.IsCounter).ToArray();
-
+            var flatten= storage.Config.BaseTypeStorageConfig.Properties.
+                Where(propertyStorage => propertyStorage.FlattenProperties.Any()).ToArray();
+            while (flatten.Any())
+            {
+                var flattenCounters = flatten.SelectMany(p => p.FlattenProperties.Where(fp => fp.IsCounter)).ToArray();
+                counterProperties = counterProperties.Concat(flattenCounters).ToArray();
+                flatten = flatten.SelectMany(p => p.FlattenProperties.Where(fp => fp.FlattenProperties.Any())).ToArray();
+            }
+
+
             return counterProperties;
         }
 
@@ -541,6 +551,8 @@ private void PopulateItemStorage(object toStore, ItemStorage storage, DynamoDBFl
                     storageConfig = config.BaseTypeStorageConfig;
                 }
 
+                var now = AWSSDKUtils.CorrectedUtcNow;
+
                 foreach (PropertyStorage propertyStorage in storageConfig.AllPropertyStorage)
                 {
                     // if only keys are being serialized, skip non-key properties
@@ -557,7 +569,7 @@ private void PopulateItemStorage(object toStore, ItemStorage storage, DynamoDBFl
                     object value;
                     if (TryGetValue(toStore, propertyStorage.Member, out value))
                     {
-                        DynamoDBEntry dbe = ToDynamoDBEntry(propertyStorage, value, flatConfig, propertyStorage.ShouldFlattenChildProperties);
+                        DynamoDBEntry dbe = ToDynamoDBEntry(propertyStorage, value, flatConfig);
 
                         if (ShouldSave(dbe, ignoreNullValues))
                         {
@@ -572,6 +584,14 @@ private void PopulateItemStorage(object toStore, ItemStorage storage, DynamoDBFl
                                 {
                                     document[pair.Key] = pair.Value;
                                 }
+
+                                if (propertyStorage.FlattenProperties.Any(p => p.IsVersion))
+                                {
+                                    var innerVersionProperty =
+                                        propertyStorage.FlattenProperties.First(p => p.IsVersion);
+                                    storage.CurrentVersion =
+                                        innerDocument[innerVersionProperty.AttributeName] as Primitive;
+                                }
                             }
                             else
                             {
@@ -590,6 +610,11 @@ private void PopulateItemStorage(object toStore, ItemStorage storage, DynamoDBFl
                                     storage.CurrentVersion = dbePrimitive;
                             }
                         }
+
+                        if (dbe == null && propertyStorage.IsAutoGeneratedTimestamp)
+                        {
+                            document[attributeName] = new Primitive(now.ToString("o"));
+                        }
                     }
                     else
                         throw new InvalidOperationException(

sdk/src/Services/DynamoDBv2/Custom/DataModel/InternalModel.cs

@@ -137,21 +137,36 @@ internal class PropertyStorage : SimplePropertyStorage
         public bool IsGSIKey { get { return IsGSIHashKey || IsGSIRangeKey; } }
         public bool IsIgnored { get; set; }
 
-        // whether to store DateTime as epoch seconds integer
+        /// <summary>
+        /// Whether to store DateTime as epoch seconds integer.
+        /// </summary>
         public bool StoreAsEpoch { get; set; }
 
-        // whether to store DateTime as epoch seconds integer (with support for dates AFTER 2038)
+        /// <summary>
+        /// Whether to store DateTime as epoch seconds integer (with support for dates AFTER 2038).
+        /// </summary>
         public bool StoreAsEpochLong { get; set; }
 
-        // whether to store Type Discriminator for polymorphic serialization
+        /// <summary>
+        /// Whether to store Type Discriminator for polymorphic serialization.
+        /// </summary>
         public bool PolymorphicProperty { get; set; }
 
-        // whether to store child properties at the same level as the parent property
+        /// <summary>
+        /// Whether to store child properties at the same level as the parent property.
+        /// </summary>
         public bool ShouldFlattenChildProperties { get; set; }
 
-        // whether to store property at parent level
+        /// <summary>
+        /// Whether to store property at parent level.
+        /// </summary>
         public bool IsFlattened { get; set; }
 
+        /// <summary>
+        /// Whether to store the property as a timestamp that is automatically generated.
+        /// </summary>
+        public bool IsAutoGeneratedTimestamp { get; set; }
+
         // corresponding IndexNames, if applicable
         public List<string> IndexNames { get; set; }
 
@@ -242,6 +257,9 @@ public void Validate(DynamoDBContext context)
                 if (StoreAsEpoch || StoreAsEpochLong)
                     throw new InvalidOperationException("Converter for " + PropertyName + " must not be set at the same time as StoreAsEpoch or StoreAsEpochLong is set to true");
 
+                if (IsAutoGeneratedTimestamp)
+                    throw new InvalidOperationException("Converter for " + PropertyName + " must not be set at the same time as AutoGeneratedTimestamp is set to true.");
+
                 if (!Utils.CanInstantiateConverter(ConverterType) || !Utils.ImplementsInterface(ConverterType, typeof(IPropertyConverter)))
                     throw new InvalidOperationException("Converter for " + PropertyName + " must be instantiable with no parameters and must implement IPropertyConverter");
 
@@ -250,6 +268,9 @@ public void Validate(DynamoDBContext context)
 
             if (StoreAsEpoch && StoreAsEpochLong)
                 throw new InvalidOperationException(PropertyName + " must not set both StoreAsEpoch and StoreAsEpochLong as true at the same time.");
+
+            if (IsAutoGeneratedTimestamp)
+                Utils.ValidateTimestampType(MemberType);
 
             IPropertyConverter converter;
             if (context.ConverterCache.TryGetValue(MemberType, out converter) && converter != null)
@@ -470,6 +491,8 @@ internal class ItemStorageConfig
         public string VersionPropertyName { get; private set; }
         public bool HasVersion { get { return !string.IsNullOrEmpty(VersionPropertyName); } }
 
+        public bool HasAutogeneratedProperties { get; internal set; }
+
         // attribute-to-index mapping
         public Dictionary<string, List<string>> AttributeToIndexesNameMapping { get; set; }
 
@@ -1082,6 +1105,12 @@ private static PropertyStorage MemberInfoToPropertyStorage(ItemStorageConfig con
                             propertyStorage.IsRangeKey = true;
                     }
 
+                    if (propertyAttribute is DynamoDBAutoGeneratedTimestampAttribute)
+                    {
+                        propertyStorage.IsAutoGeneratedTimestamp = true;
+                        config.HasAutogeneratedProperties = true;
+                    }
+
                     DynamoDBLocalSecondaryIndexRangeKeyAttribute lsiRangeKeyAttribute = propertyAttribute as DynamoDBLocalSecondaryIndexRangeKeyAttribute;
                     if (lsiRangeKeyAttribute != null)
                     {

sdk/src/Services/DynamoDBv2/Custom/DataModel/Utils.cs

@@ -158,6 +158,21 @@ internal static void ValidateNumericType(Type memberType)
             throw new InvalidOperationException("Version property must be of primitive, numeric, integer, nullable type (e.g. int?, long?, byte?)");
         }
 
+        internal static void ValidateTimestampType(Type memberType)
+        {
+            if (memberType.IsGenericType && memberType.GetGenericTypeDefinition() == typeof(Nullable<>) &&
+                (memberType.IsAssignableFrom(typeof(DateTime)) ||
+                 memberType.IsAssignableFrom(typeof(DateTimeOffset))))
+            {
+                return;
+            }
+            throw new InvalidOperationException(
+                $"Timestamp properties must be of type Nullable<DateTime> (DateTime?) or Nullable<DateTimeOffset> (DateTimeOffset?). " +
+                $"Invalid type: {memberType.FullName}. " +
+                "Please ensure your property is declared as 'DateTime?' or 'DateTimeOffset?'."
+            );
+        }
+
         [return: DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.PublicConstructors)]
         internal static Type GetPrimitiveElementType(Type collectionType)
         {