Add support for DynamoDBAutoGeneratedTimestampAttribute that sets current timestamp during persistence operations.

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

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

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

@@ -688,4 +688,123 @@ 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>
+    /// <remarks>
+    /// The <see cref="Mode"/> property controls when the timestamp is set:
+    /// <list type="bullet">
+    /// <item><description><see cref="TimestampMode.Create"/>: Set only when the item is created.</description></item>
+    /// <item><description><see cref="TimestampMode.Always"/>: Set on both create and update.</description></item>
+    /// </list>
+    /// </remarks>
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, Inherited = true, AllowMultiple = false)]
+    public sealed class DynamoDBAutoGeneratedTimestampAttribute : DynamoDBPropertyAttribute
+    {
+        /// <summary>
+        /// Gets or sets when the timestamp should be generated.
+        /// </summary>
+        public TimestampMode Mode { get;  }
+
+        /// <summary>
+        /// Default constructor. Timestamp is set on both create and update.
+        /// </summary>
+        public DynamoDBAutoGeneratedTimestampAttribute()
+            : base()
+        {
+            Mode = TimestampMode.Always;
+        }
+
+        /// <summary>
+        /// Constructor that specifies when the timestamp should be generated.
+        /// </summary>
+        /// <param name="mode">Specifies when the timestamp should be generated.</param>
+        public DynamoDBAutoGeneratedTimestampAttribute(TimestampMode mode)
+            : base()
+        {
+            Mode = mode;
+        }
+
+        /// <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)
+        {
+            Mode = TimestampMode.Always;
+        }
+
+        /// <summary>
+        /// Constructor that specifies an alternate attribute name and when the timestamp should be generated.
+        /// </summary>
+        /// <param name="attributeName">Name of attribute to be associated with property or field.</param>
+        /// <param name="mode">Specifies when the timestamp should be generated.</param>
+        public DynamoDBAutoGeneratedTimestampAttribute(string attributeName, TimestampMode mode)
+            : base(attributeName)
+        {
+            Mode = mode;
+        }
+
+        /// <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)
+        {
+            Mode = TimestampMode.Always;
+        }
+
+        /// <summary>
+        /// Constructor that specifies a custom converter and when the timestamp should be generated.
+        /// </summary>
+        /// <param name="converter">Custom converter type.</param>
+        /// <param name="mode">Specifies when the timestamp should be generated.</param>
+        public DynamoDBAutoGeneratedTimestampAttribute([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.Interfaces)] Type converter, TimestampMode mode)
+            : base(converter)
+        {
+            Mode = mode;
+        }
+
+        /// <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)
+        {
+            Mode = TimestampMode.Always;
+        }
+
+        /// <summary>
+        /// Constructor that specifies an alternate attribute name, a custom converter, and when the timestamp should be generated.
+        /// </summary>
+        /// <param name="attributeName">Name of attribute to be associated with property or field.</param>
+        /// <param name="converter">Custom converter type.</param>
+        /// <param name="mode">Specifies when the timestamp should be generated.</param>
+        public DynamoDBAutoGeneratedTimestampAttribute(string attributeName, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.Interfaces)] Type converter, TimestampMode mode)
+            : base(attributeName, converter)
+        {
+            Mode = mode;
+        }
+    }
+
+    /// <summary>
+    /// Specifies when an auto-generated timestamp should be set.
+    /// </summary>
+    public enum TimestampMode
+    {
+        /// <summary>
+        /// Set the timestamp only when the item is created.
+        /// </summary>
+        Create,
+        /// <summary>
+        /// Set the timestamp on both create and update.
+        /// </summary>
+        Always
+    }
 }

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

@@ -375,17 +375,23 @@ public IMultiTableTransactWrite CreateMultiTableTransactWrite(params ITransactWr
 
             var counterConditionExpression = BuildCounterConditionExpression(storage);
 
+            var autoGeneratedTimestampExpression = BuildTimestampConditionExpression(storage);
+
             Document updateDocument;
             Expression versionExpression = null;
-
-            var returnValues=counterConditionExpression == null ? ReturnValues.None : ReturnValues.AllNewAttributes;
+
+            var updateExpression = Expression.MergeUpdateExpressions(counterConditionExpression, autoGeneratedTimestampExpression);
+
+            var returnValues = updateExpression == null 
+                ? ReturnValues.None
+                : ReturnValues.AllNewAttributes;
 
             if ((flatConfig.SkipVersionCheck.HasValue && flatConfig.SkipVersionCheck.Value) || !storage.Config.HasVersion)
             {
                 updateDocument = table.UpdateHelper(storage.Document, table.MakeKey(storage.Document), new UpdateItemOperationConfig()
                 {
                     ReturnValues = returnValues
-                }, counterConditionExpression);
+                }, updateExpression);
             }
             else
             {
@@ -398,10 +404,10 @@ public IMultiTableTransactWrite CreateMultiTableTransactWrite(params ITransactWr
                     ReturnValues = returnValues,
                     ConditionalExpression = versionExpression,
                 };
-                updateDocument = table.UpdateHelper(storage.Document, table.MakeKey(storage.Document), updateItemOperationConfig, counterConditionExpression);
+                updateDocument = table.UpdateHelper(storage.Document, table.MakeKey(storage.Document), updateItemOperationConfig, updateExpression);
             }
 
-            if (counterConditionExpression == null && versionExpression == null) return;
+            if (updateExpression == null && versionExpression == null) return;
 
             if (returnValues == ReturnValues.AllNewAttributes)
             {
@@ -428,10 +434,16 @@ private async Task SaveHelperAsync([DynamicallyAccessedMembers(InternalConstants
 
             var counterConditionExpression = BuildCounterConditionExpression(storage);
 
+            var autoGeneratedTimestampExpression = BuildTimestampConditionExpression(storage);
+
             Document updateDocument;
             Expression versionExpression = null;
 
-            var returnValues = counterConditionExpression == null ? ReturnValues.None : ReturnValues.AllNewAttributes;
+            var updateExpression = Expression.MergeUpdateExpressions(counterConditionExpression, autoGeneratedTimestampExpression);
+
+            var returnValues = updateExpression == null
+                ? ReturnValues.None
+                : ReturnValues.AllNewAttributes;
 
             if (
                 (flatConfig.SkipVersionCheck.HasValue && flatConfig.SkipVersionCheck.Value)
@@ -440,7 +452,7 @@ private async Task SaveHelperAsync([DynamicallyAccessedMembers(InternalConstants
                 updateDocument = await table.UpdateHelperAsync(storage.Document, table.MakeKey(storage.Document), new UpdateItemOperationConfig
                 {
                     ReturnValues = returnValues
-                }, counterConditionExpression, cancellationToken).ConfigureAwait(false);
+                }, updateExpression, cancellationToken).ConfigureAwait(false);
             }
             else
             {
@@ -455,12 +467,12 @@ private async Task SaveHelperAsync([DynamicallyAccessedMembers(InternalConstants
                     {
                         ReturnValues = returnValues,
                         ConditionalExpression = versionExpression
-                    }, counterConditionExpression,
+                    }, updateExpression,
                     cancellationToken)
                     .ConfigureAwait(false);
             }
 
-            if (counterConditionExpression == null && versionExpression == null) return;
+            if (updateExpression == null && versionExpression == null) return;
 
             if (returnValues == ReturnValues.AllNewAttributes)
             {

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

@@ -26,6 +26,7 @@
 using Amazon.Util.Internal;
 using System.Globalization;
 using System.Diagnostics.CodeAnalysis;
+using Amazon.Util;
 using ThirdParty.RuntimeBackports;
 
 namespace Amazon.DynamoDBv2.DataModel
@@ -118,6 +119,86 @@ internal static Expression CreateConditionExpressionForVersion(ItemStorage stora
 
         #endregion
 
+        #region Autogenerated Timestamp
+
+        internal static Expression BuildTimestampConditionExpression(ItemStorage storage)
+        {
+            var timestampProperties = GetTimestampProperties(storage);
+            Expression timestampConditionExpression = null;
+
+            if (timestampProperties.Length != 0)
+            {
+                timestampConditionExpression = CreateUpdateExpressionForTimestampProperties(timestampProperties);
+            }
+
+            return timestampConditionExpression;
+        }
+
+        private static Expression CreateUpdateExpressionForTimestampProperties(PropertyStorage[] timestampProperties)
+        {
+            if (timestampProperties == null || timestampProperties.Length == 0)
+                return null;
+
+            var updateExpression = new Expression();
+            var setClauses = new List<string>();
+
+            var dateTime = AWSSDKUtils.CorrectedUtcNow; // Use corrected UTC time
+            foreach (var propertyStorage in timestampProperties)
+            {
+                string attributeName = propertyStorage.AttributeName;
+                string attributeRef = Common.GetAttributeReference(attributeName);
+                string valueRef = $":{attributeName}Timestamp";
+                updateExpression.ExpressionAttributeNames[attributeRef] = attributeName;
+
+                if (propertyStorage.StoreAsEpochLong)
+                {
+                    string epochSecondsAsString = AWSSDKUtils.ConvertToUnixEpochSecondsString(dateTime);
+                    updateExpression.ExpressionAttributeValues[valueRef] = new Primitive(epochSecondsAsString, saveAsNumeric: true);
+                }
+                else if (propertyStorage.StoreAsEpoch)
+                {
+                    updateExpression.ExpressionAttributeValues[valueRef] = AWSSDKUtils.ConvertToUnixEpochSeconds(dateTime);
+                }
+                else
+                {
+                    updateExpression.ExpressionAttributeValues[valueRef] = dateTime.ToString("o");
+                }
+
+                // Determine SET clause based on TimestampMode
+                string clause;
+                var mode = propertyStorage.AutoGeneratedTimestampMode;
+                switch (mode)
+                {
+                    case TimestampMode.Create:
+                        clause = $"{attributeRef} = if_not_exists({attributeRef}, {valueRef})";
+                        break;
+                    case TimestampMode.Always:
+                    default:
+                        clause = $"{attributeRef} = {valueRef}";
+                        break;
+                }
+                setClauses.Add(clause);
+            }
+
+            if (setClauses.Count > 0)
+            {
+                updateExpression.ExpressionStatement = "SET " + string.Join(", ", setClauses);
+            }
+
+            return updateExpression;
+        }
+
+        private static PropertyStorage[] GetTimestampProperties(ItemStorage storage)
+        {
+            //todo : adapt this to work with polymorphic types
+            var counterProperties = storage.Config.BaseTypeStorageConfig.AllPropertyStorage.
+                Where(propertyStorage => propertyStorage.IsAutoGeneratedTimestamp).ToArray();
+
+            return counterProperties;
+        }
+
+        #endregion
+
         #region Atomic counters
 
         internal static Expression BuildCounterConditionExpression(ItemStorage storage)
@@ -135,7 +216,7 @@ internal static Expression BuildCounterConditionExpression(ItemStorage storage)
 
         private static PropertyStorage[] GetCounterProperties(ItemStorage storage)
         {
-            var counterProperties = storage.Config.BaseTypeStorageConfig.Properties.
+            var counterProperties = storage.Config.BaseTypeStorageConfig.AllPropertyStorage.
                 Where(propertyStorage => propertyStorage.IsCounter).ToArray();
 
             return counterProperties;
@@ -570,6 +651,14 @@ 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
                             {