diff --git a/examples/pdf_embedding/main.py b/examples/pdf_embedding/main.py
index 0f7994ba1..a87ea9ab3 100644
--- a/examples/pdf_embedding/main.py
+++ b/examples/pdf_embedding/main.py
@@ -55,13 +55,14 @@ def pdf_embedding_flow(flow_builder: cocoindex.FlowBuilder, data_scope: cocoinde
 
         with doc["chunks"].row() as chunk:
             chunk["embedding"] = chunk["text"].call(text_to_embedding)
-            doc_embeddings.collect(filename=doc["filename"], location=chunk["location"],
+            doc_embeddings.collect(id=cocoindex.GeneratedField.UUID,
+                                   filename=doc["filename"], location=chunk["location"],
                                    text=chunk["text"], embedding=chunk["embedding"])
 
     doc_embeddings.export(
         "doc_embeddings",
         cocoindex.storages.Postgres(),
-        primary_key_fields=["filename", "location"],
+        primary_key_fields=["id"],
         vector_index=[("embedding", cocoindex.VectorSimilarityMetric.COSINE_SIMILARITY)])
 
 query_handler = cocoindex.query.SimpleSemanticsQueryHandler(
diff --git a/python/cocoindex/__init__.py b/python/cocoindex/__init__.py
index 8c9916777..81397f404 100644
--- a/python/cocoindex/__init__.py
+++ b/python/cocoindex/__init__.py
@@ -2,7 +2,8 @@
 Cocoindex is a framework for building and running indexing pipelines.
 """
 from . import flow, functions, query, sources, storages, cli
-from .flow import FlowBuilder, DataScope, DataSlice, Flow, flow_def, EvaluateAndDumpOptions
+from .flow import FlowBuilder, DataScope, DataSlice, Flow, flow_def
+from .flow import EvaluateAndDumpOptions, GeneratedField
 from .llm import LlmSpec, LlmApiType
 from .vector import VectorSimilarityMetric
 from .lib import *
diff --git a/python/cocoindex/flow.py b/python/cocoindex/flow.py
index 23fc88721..2ace32df2 100644
--- a/python/cocoindex/flow.py
+++ b/python/cocoindex/flow.py
@@ -238,6 +238,12 @@ def add_collector(self, name: str | None = None) -> DataCollector:
             )
         )
 
+class GeneratedField(Enum):
+    """
+    A generated field is automatically set by the engine.
+    """
+    UUID = "Uuid"
+
 class DataCollector:
     """A data collector is used to collect data into a collector."""
     _flow_builder_state: _FlowBuilderState
@@ -248,12 +254,25 @@ def __init__(self, flow_builder_state: _FlowBuilderState,
         self._flow_builder_state = flow_builder_state
         self._engine_data_collector = data_collector
 
-    def collect(self, **kwargs: DataSlice):
+    def collect(self, **kwargs: DataSlice | GeneratedField):
         """
         Collect data into the collector.
         """
+        regular_kwargs = []
+        auto_uuid_field = None
+        for k, v in kwargs.items():
+            if isinstance(v, GeneratedField):
+                if v == GeneratedField.UUID:
+                    if auto_uuid_field is not None:
+                        raise ValueError("Only one generated UUID field is allowed")
+                    auto_uuid_field = k
+                else:
+                    raise ValueError(f"Unexpected generated field: {v}")
+            else:
+                regular_kwargs.append((k, _data_slice_state(v).engine_data_slice))
+
         self._flow_builder_state.engine_flow_builder.collect(
-            self._engine_data_collector, [(k, _data_slice_state(v).engine_data_slice) for k, v in kwargs.items()])
+            self._engine_data_collector, regular_kwargs, auto_uuid_field)
 
     def export(self, name: str, target_spec: op.StorageSpec, /, *,
               primary_key_fields: Sequence[str] | None = None,
diff --git a/src/base/schema.rs b/src/base/schema.rs
index 2a4f45c08..24537a19e 100644
--- a/src/base/schema.rs
+++ b/src/base/schema.rs
@@ -360,13 +360,13 @@ impl std::fmt::Display for CollectorSchema {
 }
 
 impl CollectorSchema {
-    pub fn from_fields(fields: Vec<FieldSchema>, has_auto_uuid_field: bool) -> Self {
+    pub fn from_fields(fields: Vec<FieldSchema>, auto_uuid_field: Option<FieldName>) -> Self {
         let mut fields = fields;
-        let auto_uuid_field_idx = if has_auto_uuid_field {
+        let auto_uuid_field_idx = if let Some(auto_uuid_field) = auto_uuid_field {
             fields.insert(
                 0,
                 FieldSchema::new(
-                    "uuid".to_string(),
+                    auto_uuid_field,
                     EnrichedValueType {
                         typ: ValueType::Basic(BasicValueType::Uuid),
                         nullable: false,
diff --git a/src/builder/analyzer.rs b/src/builder/analyzer.rs
index 8095d1112..b50ba7b01 100644
--- a/src/builder/analyzer.rs
+++ b/src/builder/analyzer.rs
@@ -799,7 +799,7 @@ impl AnalyzerContext<'_> {
                     collector_ref: add_collector(
                         &op.scope_name,
                         op.collector_name.clone(),
-                        CollectorSchema::from_fields(fields_schema, has_auto_uuid_field),
+                        CollectorSchema::from_fields(fields_schema, op.auto_uuid_field.clone()),
                         scopes,
                     )?,
                     fingerprinter,
diff --git a/src/builder/flow_builder.rs b/src/builder/flow_builder.rs
index 3e4361920..53f966316 100644
--- a/src/builder/flow_builder.rs
+++ b/src/builder/flow_builder.rs
@@ -543,7 +543,7 @@ impl FlowBuilder {
                         },
                         scope_name: collector.scope.scope_name.clone(),
                         collector_name: collector.name.clone(),
-                        auto_uuid_field,
+                        auto_uuid_field: auto_uuid_field.clone(),
                     }),
                 };
 
@@ -565,7 +565,7 @@ impl FlowBuilder {
                     value_type: ds.data_type.schema,
                 })
                 .collect(),
-            has_auto_uuid_field,
+            auto_uuid_field,
         );
         {
             let mut collector = collector.collector.lock().unwrap();