diff --git a/api/core/indexing_runner.py b/api/core/indexing_runner.py
index 52776ee626..04d8293ccb 100644
--- a/api/core/indexing_runner.py
+++ b/api/core/indexing_runner.py
@@ -38,7 +38,14 @@ from extensions.ext_storage import storage
 from libs import helper
 from libs.datetime_utils import naive_utc_now
 from models import Account
-from models.dataset import AutomaticRulesConfig, ChildChunk, Dataset, DatasetProcessRule, DocumentSegment
+from models.dataset import (
+    AutomaticRulesConfig,
+    ChildChunk,
+    Dataset,
+    DatasetProcessRule,
+    DocumentSegment,
+    ProcessRuleDict,
+)
 from models.dataset import Document as DatasetDocument
 from models.enums import DataSourceType, IndexingStatus, ProcessRuleMode, SegmentStatus
 from models.model import UploadFile
@@ -318,10 +325,11 @@ class IndexingRunner:
         index_processor = IndexProcessorFactory(index_type).init_index_processor()
         # one extract_setting is one source document
         for extract_setting in extract_settings:
-            # extract
-            processing_rule = DatasetProcessRule(
-                mode=tmp_processing_rule["mode"], rules=json.dumps(tmp_processing_rule["rules"])
-            )
+            # Preview only needs the rule payload, not a persisted ORM record.
+            processing_rule: ProcessRuleDict = {
+                "mode": tmp_processing_rule["mode"],
+                "rules": tmp_processing_rule.get("rules"),
+            }
             # Extract document content
             text_docs = index_processor.extract(extract_setting, process_rule_mode=tmp_processing_rule["mode"])
             # Cleaning and segmentation
@@ -329,7 +337,7 @@ class IndexingRunner:
                 text_docs,
                 current_user=None,
                 embedding_model_instance=embedding_model_instance,
-                process_rule=processing_rule.to_dict(),
+                process_rule=processing_rule,
                 tenant_id=tenant_id,
                 doc_language=doc_language,
                 preview=True,
diff --git a/api/models/dataset.py b/api/models/dataset.py
index b4fb03a7f4..effb6aeeab 100644
--- a/api/models/dataset.py
+++ b/api/models/dataset.py
@@ -11,7 +11,7 @@ import time
 from collections.abc import Sequence
 from datetime import datetime
 from json import JSONDecodeError
-from typing import Any, TypedDict, cast
+from typing import Any, NotRequired, TypedDict, cast
 from uuid import uuid4
 
 import sqlalchemy as sa
@@ -70,8 +70,8 @@ class AutomaticRulesConfig(TypedDict):
 
 
 class ProcessRuleDict(TypedDict):
-    id: str
-    dataset_id: str
+    id: NotRequired[str]
+    dataset_id: NotRequired[str]
     mode: str
     rules: dict[str, Any] | None
 
diff --git a/api/tests/unit_tests/core/rag/indexing/test_indexing_runner.py b/api/tests/unit_tests/core/rag/indexing/test_indexing_runner.py
index b011ade884..cf24dcf544 100644
--- a/api/tests/unit_tests/core/rag/indexing/test_indexing_runner.py
+++ b/api/tests/unit_tests/core/rag/indexing/test_indexing_runner.py
@@ -1431,6 +1431,44 @@ class TestIndexingRunnerEstimate:
                     doc_form=IndexStructureType.PARAGRAPH_INDEX,
                 )
 
+    def test_indexing_estimate_uses_lightweight_preview_process_rule(self, mock_dependencies):
+        """Test preview estimation avoids constructing a persisted DatasetProcessRule ORM object."""
+        # Arrange
+        runner = IndexingRunner()
+        tenant_id = str(uuid.uuid4())
+        extract_setting = MagicMock()
+        tmp_processing_rule = create_mock_process_rule(mode="automatic")
+
+        mock_features = MagicMock()
+        mock_features.billing.enabled = False
+        mock_dependencies["feature_service"].get_features.return_value = mock_features
+
+        mock_processor = MagicMock()
+        mock_processor.extract.return_value = [Document(page_content="source", metadata={"doc_id": "source-1"})]
+        mock_processor.transform.return_value = [Document(page_content="preview chunk", metadata={"doc_id": "chunk-1"})]
+        mock_dependencies["factory"].return_value.init_index_processor.return_value = mock_processor
+
+        with patch("core.indexing_runner.DatasetProcessRule", side_effect=AssertionError("ORM should not be created")):
+            # Act
+            estimate = runner.indexing_estimate(
+                tenant_id=tenant_id,
+                extract_settings=[extract_setting],
+                tmp_processing_rule=tmp_processing_rule,
+                doc_form=IndexStructureType.PARAGRAPH_INDEX,
+            )
+
+        # Assert
+        assert estimate.total_segments == 1
+        assert len(estimate.preview) == 1
+        assert estimate.preview[0].content == "preview chunk"
+
+        transform_kwargs = mock_processor.transform.call_args.kwargs
+        assert transform_kwargs["preview"] is True
+        assert transform_kwargs["process_rule"] == {
+            "mode": tmp_processing_rule["mode"],
+            "rules": tmp_processing_rule.get("rules"),
+        }
+
 
 class TestIndexingRunnerProcessChunk:
     """Unit tests for chunk processing in parallel.