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 +688,108 @@ 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)
+        {
+        }
+    }
+
+    /// <summary>
+    /// Specifies the update behavior for a property when performing DynamoDB update operations.
+    /// This attribute can be used to control whether a property is always updated, only updated if not null,
+    /// or ignored during update operations.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, Inherited = true, AllowMultiple = false)]
+    public sealed class DynamoDbUpdateBehaviorAttribute : DynamoDBPropertyAttribute
+    {
+        /// <summary>
+        /// Gets the update behavior for the property.
+        /// </summary>
+        public UpdateBehavior Behavior { get; }
+
+        /// <summary>
+        /// Default constructor. Sets behavior to Always.
+        /// </summary>
+        public DynamoDbUpdateBehaviorAttribute()
+            : base()
+        {
+            Behavior = UpdateBehavior.Always;
+        }
+
+        /// <summary>
+        /// Constructor that specifies the update behavior.
+        /// </summary>
+        /// <param name="behavior">The update behavior to apply.</param>
+        public DynamoDbUpdateBehaviorAttribute(UpdateBehavior behavior)
+            : base()
+        {
+            Behavior = behavior;
+        }
+
+        /// <summary>
+        /// Constructor that specifies an alternate attribute name and update behavior.
+        /// </summary>
+        /// <param name="attributeName">Name of attribute to be associated with property or field.</param>
+        /// <param name="behavior">The update behavior to apply.</param>
+        public DynamoDbUpdateBehaviorAttribute(string attributeName, UpdateBehavior behavior)
+            : base(attributeName)
+        {
+            Behavior = behavior;
+        }
+    }
+
+    /// <summary>
+    /// Specifies when a property value should be set.
+    /// </summary>
+    public enum UpdateBehavior
+    {
+        /// <summary>
+        /// Set the value on both create and update.
+        /// </summary>
+        Always,
+        /// <summary>
+        /// Set the value only when the item is created.
+        /// </summary>
+        IfNotExists
+    }
 }

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

@@ -377,31 +377,37 @@ public IMultiTableTransactWrite CreateMultiTableTransactWrite(params ITransactWr
 
             Document updateDocument;
             Expression versionExpression = null;
-
-            var returnValues=counterConditionExpression == null ? ReturnValues.None : ReturnValues.AllNewAttributes;
 
-            if ((flatConfig.SkipVersionCheck.HasValue && flatConfig.SkipVersionCheck.Value) || !storage.Config.HasVersion)
+            SetNewTimestamps(storage);
+
+            var updateIfNotExists = GetUpdateIfNotExistsAttributeNames(storage);
+
+            var returnValues = counterConditionExpression == null && !updateIfNotExists.Any()
+                ? ReturnValues.None
+                : ReturnValues.AllNewAttributes;
+
+            var updateItemOperationConfig = new UpdateItemOperationConfig
             {
-                updateDocument = table.UpdateHelper(storage.Document, table.MakeKey(storage.Document), new UpdateItemOperationConfig()
-                {
-                    ReturnValues = returnValues
-                }, counterConditionExpression);
-            }
-            else
+                ReturnValues = returnValues
+            };
+
+            if (!(flatConfig.SkipVersionCheck.HasValue && flatConfig.SkipVersionCheck.Value) && storage.Config.HasVersion)
             {
-                var conversionConfig = new DynamoDBEntry.AttributeConversionConfig(table.Conversion, table.IsEmptyStringValueEnabled); 
+                var conversionConfig = new DynamoDBEntry.AttributeConversionConfig(table.Conversion, table.IsEmptyStringValueEnabled);
                 versionExpression = CreateConditionExpressionForVersion(storage, conversionConfig);
                 SetNewVersion(storage);
-
-                var updateItemOperationConfig = new UpdateItemOperationConfig
-                {
-                    ReturnValues = returnValues,
-                    ConditionalExpression = versionExpression,
-                };
-                updateDocument = table.UpdateHelper(storage.Document, table.MakeKey(storage.Document), updateItemOperationConfig, counterConditionExpression);
+                updateItemOperationConfig.ConditionalExpression = versionExpression;
             }
 
-            if (counterConditionExpression == null && versionExpression == null) return;
+            updateDocument = table.UpdateHelper(
+                storage.Document,
+                table.MakeKey(storage.Document),
+                updateItemOperationConfig,
+                counterConditionExpression,
+                updateIfNotExists
+            );
+
+            if (counterConditionExpression == null && versionExpression == null && !updateIfNotExists.Any()) return;
 
             if (returnValues == ReturnValues.AllNewAttributes)
             {
@@ -431,36 +437,38 @@ private async Task SaveHelperAsync([DynamicallyAccessedMembers(InternalConstants
             Document updateDocument;
             Expression versionExpression = null;
 
-            var returnValues = counterConditionExpression == null ? ReturnValues.None : ReturnValues.AllNewAttributes;
+            SetNewTimestamps(storage);
+
+            var updateIfNotExistsAttributeName = GetUpdateIfNotExistsAttributeNames(storage);
 
-            if (
-                (flatConfig.SkipVersionCheck.HasValue && flatConfig.SkipVersionCheck.Value)
-                || !storage.Config.HasVersion)
+            var returnValues = counterConditionExpression == null && !updateIfNotExistsAttributeName.Any()
+                ? ReturnValues.None
+                : ReturnValues.AllNewAttributes;
+
+            var updateItemOperationConfig = new UpdateItemOperationConfig
             {
-                updateDocument = await table.UpdateHelperAsync(storage.Document, table.MakeKey(storage.Document), new UpdateItemOperationConfig
-                {
-                    ReturnValues = returnValues
-                }, counterConditionExpression, cancellationToken).ConfigureAwait(false);
-            }
-            else
+                ReturnValues = returnValues
+            };
+
+            if (!(flatConfig.SkipVersionCheck.HasValue && flatConfig.SkipVersionCheck.Value) && storage.Config.HasVersion)
             {
-                var conversionConfig = new DynamoDBEntry.AttributeConversionConfig(table.Conversion, table.IsEmptyStringValueEnabled); 
+                var conversionConfig = new DynamoDBEntry.AttributeConversionConfig(table.Conversion, table.IsEmptyStringValueEnabled);
                 versionExpression = CreateConditionExpressionForVersion(storage, conversionConfig);
                 SetNewVersion(storage);
-
-                updateDocument = await table.UpdateHelperAsync(
-                    storage.Document,
-                    table.MakeKey(storage.Document),
-                    new UpdateItemOperationConfig
-                    {
-                        ReturnValues = returnValues,
-                        ConditionalExpression = versionExpression
-                    }, counterConditionExpression,
-                    cancellationToken)
-                    .ConfigureAwait(false);
+                updateItemOperationConfig.ConditionalExpression = versionExpression;
             }
 
-            if (counterConditionExpression == null && versionExpression == null) return;
+            updateDocument = await table.UpdateHelperAsync(
+                storage.Document,
+                table.MakeKey(storage.Document),
+                updateItemOperationConfig,
+                counterConditionExpression,
+                cancellationToken,
+                updateIfNotExistsAttributeName
+            ).ConfigureAwait(false);
+
+
+            if (counterConditionExpression == null && versionExpression == null && !updateIfNotExistsAttributeName.Any()) 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
@@ -59,6 +60,7 @@ internal static void SetNewVersion(ItemStorage storage)
             }
             storage.Document[versionAttributeName] = version;
         }
+
         private static void IncrementVersion(Type memberType, ref Primitive version)
         {
             if (memberType.IsAssignableFrom(typeof(Byte))) version = version.AsByte() + 1;
@@ -118,6 +120,40 @@ internal static Expression CreateConditionExpressionForVersion(ItemStorage stora
 
         #endregion
 
+        #region Autogenerated Timestamp
+
+        internal static void SetNewTimestamps(ItemStorage storage)
+        {
+            var timestampProperties = GetTimestampProperties(storage);
+            if (timestampProperties.Length == 0) return;
+
+            var now = AWSSDKUtils.CorrectedUtcNow;
+
+            foreach (var timestampProperty in timestampProperties)
+            {
+                var attributeName = timestampProperty.AttributeName;
+
+                storage.Document[attributeName] = new Primitive(now.ToString("o"));
+            }
+        }
+
+        internal static bool HasCreateOnlyProperties(ItemStorage storage)
+        {
+            return storage.Config.BaseTypeStorageConfig.AllPropertyStorage
+                .Any(propertyStorage => propertyStorage.UpdateBehaviorMode == UpdateBehavior.IfNotExists);
+        }
+
+        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 +171,7 @@ 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;
@@ -163,10 +199,16 @@ private static Expression CreateUpdateExpressionForCounterProperties(PropertySto
                     propertyStorage.CounterStartValue - propertyStorage.CounterDelta;
             }
             updateExpression.ExpressionStatement = $"SET {asserts.Substring(0, asserts.Length - 2)}";
-
             return updateExpression;
         }
 
+        internal static List<string> GetUpdateIfNotExistsAttributeNames(ItemStorage storage)
+        {
+            var timestampProperties = storage.Config.BaseTypeStorageConfig.AllPropertyStorage
+                .Where(propertyStorage => propertyStorage.UpdateBehaviorMode == UpdateBehavior.IfNotExists).ToArray();
+            return timestampProperties.Select(p => p.AttributeName).ToList();
+        }
+
         #endregion
 
         #region Table methods
@@ -570,6 +612,14 @@ 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
                             {