support ReturnValuesOnConditionCheckFailure (#245)

conditioncheck.go

@@ -86,6 +86,7 @@ func (check *ConditionCheck) writeTxItem() (*types.TransactWriteItem, error) {
 	}
 	if check.condition != "" {
 		item.ConditionExpression = aws.String(check.condition)
+		item.ReturnValuesOnConditionCheckFailure = types.ReturnValuesOnConditionCheckFailureAllOld
 	}
 	return &types.TransactWriteItem{
 		ConditionCheck: item,

db.go

@@ -203,6 +203,45 @@ func IsCondCheckFailed(err error) bool {
 	return false
 }
 
-// type noopLogger struct{}
+// Unmarshals an item from a ConditionalCheckFailedException into `out`, with the same behavior as [UnmarshalItem].
+// The return value boolean `match` will be true if condCheckErr is a ConditionalCheckFailedException,
+// otherwise false if it is nil or a different error.
+func UnmarshalItemFromCondCheckFailed(condCheckErr error, out any) (match bool, err error) {
+	if condCheckErr == nil {
+		return false, nil
+	}
+	var cfe *types.ConditionalCheckFailedException
+	if errors.As(condCheckErr, &cfe) {
+		if cfe.Item == nil {
+			return true, fmt.Errorf("dynamo: ConditionalCheckFailedException does not contain item")
+		}
+		return true, UnmarshalItem(cfe.Item, out)
+	}
+	return false, condCheckErr
+}
 
-// func (noopLogger) Log(...interface{}) {}
+// Unmarshals items from a TransactionCanceledException by appending them to `out`, which must be a pointer to a slice.
+// The return value boolean `match` will be true if txCancelErr is a TransactionCanceledException with at least one ConditionalCheckFailed cancellation reason,
+// otherwise false if it is nil or a different error.
+func UnmarshalItemsFromTxCondCheckFailed(txCancelErr error, out any) (match bool, err error) {
+	if txCancelErr == nil {
+		return false, nil
+	}
+	unmarshal := unmarshalAppendTo(out)
+	var txe *types.TransactionCanceledException
+	if errors.As(txCancelErr, &txe) {
+		for _, cr := range txe.CancellationReasons {
+			if cr.Code != nil && *cr.Code == "ConditionalCheckFailed" {
+				if cr.Item == nil {
+					return true, fmt.Errorf("dynamo: TransactionCanceledException.CancellationReasons does not contain item")
+				}
+				if err = unmarshal(cr.Item, out); err != nil {
+					return true, err
+				}
+				match = true
+			}
+		}
+		return match, nil
+	}
+	return false, txCancelErr
+}

delete.go

@@ -12,7 +12,7 @@ import (
 // See: http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_DeleteItem.html
 type Delete struct {
 	table      Table
-	returnType string
+	returnType types.ReturnValue
 
 	hashKey   string
 	hashValue types.AttributeValue
@@ -79,15 +79,15 @@ func (d *Delete) ConsumedCapacity(cc *ConsumedCapacity) *Delete {
 
 // Run executes this delete request.
 func (d *Delete) Run(ctx context.Context) error {
-	d.returnType = "NONE"
+	d.returnType = types.ReturnValueNone
 	_, err := d.run(ctx)
 	return err
 }
 
 // OldValue executes this delete request, unmarshaling the previous value to out.
 // Returns ErrNotFound is there was no previous value.
 func (d *Delete) OldValue(ctx context.Context, out interface{}) error {
-	d.returnType = "ALL_OLD"
+	d.returnType = types.ReturnValueAllOld
 	output, err := d.run(ctx)
 	switch {
 	case err != nil:
@@ -98,6 +98,26 @@ func (d *Delete) OldValue(ctx context.Context, out interface{}) error {
 	return unmarshalItem(output.Attributes, out)
 }
 
+// CurrentValue executes this delete.
+// If successful, the return value `deleted` will be true, and nothing will be unmarshaled to `out`
+//
+// If the delete is unsuccessful because of a condition check failure, `deleted` will be false, the current value of the item will be unmarshaled to `out`, and `err` will be nil.
+//
+// If the delete is unsuccessful for any other reason, `deleted` will be false and `err` will be non-nil.
+//
+// See also: [UnmarshalItemFromCondCheckFailed].
+func (d *Delete) CurrentValue(ctx context.Context, out interface{}) (wrote bool, err error) {
+	d.returnType = types.ReturnValueNone
+	_, err = d.run(ctx)
+	if err != nil {
+		if ok, err := UnmarshalItemFromCondCheckFailed(err, out); ok {
+			return false, err
+		}
+		return false, err
+	}
+	return true, nil
+}
+
 func (d *Delete) run(ctx context.Context) (*dynamodb.DeleteItemOutput, error) {
 	if d.err != nil {
 		return nil, d.err
@@ -121,12 +141,13 @@ func (d *Delete) deleteInput() *dynamodb.DeleteItemInput {
 	input := &dynamodb.DeleteItemInput{
 		TableName:                 &d.table.name,
 		Key:                       d.key(),
-		ReturnValues:              types.ReturnValue(d.returnType),
+		ReturnValues:              d.returnType,
 		ExpressionAttributeNames:  d.nameExpr,
 		ExpressionAttributeValues: d.valueExpr,
 	}
 	if d.condition != "" {
 		input.ConditionExpression = &d.condition
+		input.ReturnValuesOnConditionCheckFailure = types.ReturnValuesOnConditionCheckFailureAllOld
 	}
 	if d.cc != nil {
 		input.ReturnConsumedCapacity = types.ReturnConsumedCapacityIndexes
@@ -141,11 +162,12 @@ func (d *Delete) writeTxItem() (*types.TransactWriteItem, error) {
 	input := d.deleteInput()
 	item := &types.TransactWriteItem{
 		Delete: &types.Delete{
-			TableName:                 input.TableName,
-			Key:                       input.Key,
-			ExpressionAttributeNames:  input.ExpressionAttributeNames,
-			ExpressionAttributeValues: input.ExpressionAttributeValues,
-			ConditionExpression:       input.ConditionExpression,
+			TableName:                           input.TableName,
+			Key:                                 input.Key,
+			ExpressionAttributeNames:            input.ExpressionAttributeNames,
+			ExpressionAttributeValues:           input.ExpressionAttributeValues,
+			ConditionExpression:                 input.ConditionExpression,
+			ReturnValuesOnConditionCheckFailure: input.ReturnValuesOnConditionCheckFailure,
 		},
 	}
 	return item, nil

delete_test.go

@@ -29,13 +29,17 @@ func TestDelete(t *testing.T) {
 	}
 
 	// fail to delete it
-	err = table.Delete("UserID", item.UserID).
+	var curr widget
+	wrote, err := table.Delete("UserID", item.UserID).
 		Range("Time", item.Time).
 		If("Meta.'color' = ?", "octarine").
 		If("Msg = ?", "wrong msg").
-		Run(ctx)
-	if !IsCondCheckFailed(err) {
-		t.Error("expected ConditionalCheckFailedException, not", err)
+		CurrentValue(ctx, &curr)
+	if wrote {
+		t.Error("wrote should be false")
+	}
+	if !reflect.DeepEqual(curr, item) {
+		t.Errorf("bad value. %#v ≠ %#v", curr, item)
 	}
 
 	// delete it

go.mod

@@ -1,24 +1,24 @@
 module github.com/guregu/dynamo/v2
 
 require (
-	github.com/aws/aws-sdk-go-v2 v1.30.3
+	github.com/aws/aws-sdk-go-v2 v1.30.4
 	github.com/aws/aws-sdk-go-v2/config v1.11.0
 	github.com/aws/aws-sdk-go-v2/credentials v1.6.4
-	github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue v1.14.9
-	github.com/aws/aws-sdk-go-v2/service/dynamodb v1.34.3
-	github.com/aws/smithy-go v1.20.3
+	github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue v1.14.11
+	github.com/aws/aws-sdk-go-v2/service/dynamodb v1.34.5
+	github.com/aws/smithy-go v1.20.4
 	github.com/cenkalti/backoff/v4 v4.3.0
-	golang.org/x/sync v0.7.0
+	golang.org/x/sync v0.8.0
 )
 
 require (
 	github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.8.2 // indirect
-	github.com/aws/aws-sdk-go-v2/internal/configsources v1.3.15 // indirect
-	github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.6.15 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/configsources v1.3.16 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.6.16 // indirect
 	github.com/aws/aws-sdk-go-v2/internal/ini v1.3.2 // indirect
-	github.com/aws/aws-sdk-go-v2/service/dynamodbstreams v1.22.3 // indirect
-	github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.11.3 // indirect
-	github.com/aws/aws-sdk-go-v2/service/internal/endpoint-discovery v1.9.16 // indirect
+	github.com/aws/aws-sdk-go-v2/service/dynamodbstreams v1.22.4 // indirect
+	github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.11.4 // indirect
+	github.com/aws/aws-sdk-go-v2/service/internal/endpoint-discovery v1.9.17 // indirect
 	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.5.2 // indirect
 	github.com/aws/aws-sdk-go-v2/service/sso v1.6.2 // indirect
 	github.com/aws/aws-sdk-go-v2/service/sts v1.11.1 // indirect