diff --git a/src/datachain/lib/udf.py b/src/datachain/lib/udf.py
index e3fac4254..4f429316d 100644
--- a/src/datachain/lib/udf.py
+++ b/src/datachain/lib/udf.py
@@ -160,9 +160,15 @@ def hash(self) -> str:
         """
         Creates SHA hash of this UDF function. It takes into account function,
         inputs and outputs.
+
+        For function-based UDFs, hashes self._func.
+        For class-based UDFs, hashes the process method.
         """
+        # Hash user code: either _func (function-based) or process method (class-based)
+        func_to_hash = self._func if self._func else self.process
+
         parts = [
-            hash_callable(self._func),
+            hash_callable(func_to_hash),
             self.params.hash() if self.params else "",
             self.output.hash(),
         ]
diff --git a/tests/unit/test_datachain_hash.py b/tests/unit/test_datachain_hash.py
index 8950b77b2..076266847 100644
--- a/tests/unit/test_datachain_hash.py
+++ b/tests/unit/test_datachain_hash.py
@@ -1,5 +1,6 @@
 from unittest.mock import patch
 
+import pandas as pd
 import pytest
 from pydantic import BaseModel
 
@@ -7,6 +8,11 @@
 from datachain import func
 from datachain.lib.dc import C
 
+DF_DATA = {
+    "first_name": ["Alice", "Bob", "Charlie", "David", "Eva"],
+    "age": [25, 30, 35, 40, 45],
+}
+
 
 class Person(BaseModel):
     name: str
@@ -55,13 +61,55 @@ def mock_get_listing():
 
 
 def test_read_values():
-    pytest.skip(
-        "Hash of the chain started with read_values is currently inconsistent,"
-        " meaning it produces different hash every time. This happens because we"
-        " create random name dataset in the process. Correct solution would be"
-        " to calculate hash of all those input values."
+    """
+    Hash of the chain started with read_values is currently inconsistent.
+    Goal of this test is just to check it doesn't break.
+    """
+    assert dc.read_values(num=[1, 2, 3]).hash() is not None
+
+
+def test_read_csv(test_session, tmp_dir):
+    """
+    Hash of the chain started with read_csv is currently inconsistent.
+    Goal of this test is just to check it doesn't break.
+    """
+    path = tmp_dir / "test.csv"
+    pd.DataFrame(DF_DATA).to_csv(path, index=False)
+    assert dc.read_csv(path.as_uri(), session=test_session).hash() is not None
+
+
+@pytest.mark.filterwarnings("ignore::pydantic.warnings.PydanticDeprecatedSince20")
+def test_read_json(test_session, tmp_dir):
+    """
+    Hash of the chain started with read_json is currently inconsistent.
+    Goal of this test is just to check it doesn't break.
+    """
+    path = tmp_dir / "test.jsonl"
+    dc.read_pandas(pd.DataFrame(DF_DATA), session=test_session).to_jsonl(path)
+    assert (
+        dc.read_json(path.as_uri(), format="jsonl", session=test_session).hash()
+        is not None
     )
-    assert dc.read_values(num=[1, 2, 3]).hash() == ""
+
+
+def test_read_pandas(test_session, tmp_dir):
+    """
+    Hash of the chain started with read_pandas is currently inconsistent.
+    Goal of this test is just to check it doesn't break.
+    """
+    df = pd.DataFrame(DF_DATA)
+    assert dc.read_pandas(df, session=test_session).hash() is not None
+
+
+def test_read_parquet(test_session, tmp_dir):
+    """
+    Hash of the chain started with read_parquet is currently inconsistent.
+    Goal of this test is just to check it doesn't break.
+    """
+    df = pd.DataFrame(DF_DATA)
+    path = tmp_dir / "test.parquet"
+    dc.read_pandas(df, session=test_session).to_parquet(path)
+    assert dc.read_parquet(path.as_uri(), session=test_session).hash() is not None
 
 
 def test_read_storage(mock_get_listing):
diff --git a/tests/unit/test_query_steps_hash.py b/tests/unit/test_query_steps_hash.py
index 4fc1e56dd..260336c78 100644
--- a/tests/unit/test_query_steps_hash.py
+++ b/tests/unit/test_query_steps_hash.py
@@ -75,6 +75,22 @@ def custom_feature_gen(m_fr):
     )
 
 
+# Class-based UDFs for testing hash calculation
+class DoubleMapper(Mapper):
+    """Class-based Mapper that overrides process()."""
+
+    def process(self, x):
+        return x * 2
+
+
+class TripleGenerator(Generator):
+    """Class-based Generator that overrides process()."""
+
+    def process(self, x):
+        yield x * 3
+        yield x * 3 + 1
+
+
 @pytest.fixture
 def numbers_dataset(test_session):
     """
@@ -394,6 +410,12 @@ def test_subtract_hash(test_session, numbers_dataset, on, _hash):
             {"x": CustomFeature},
             "b4edceaa18ed731085e1c433a6d21deabec8d92dfc338fb1d709ed7951977fc5",
         ),
+        (
+            DoubleMapper(),
+            ["x"],
+            {"double": int},
+            "7994436106fef0486b04078b02ee437be3aa73ade2d139fb8c020e2199515e26",
+        ),
     ],
 )
 def test_udf_mapper_hash(
@@ -428,6 +450,12 @@ def test_udf_mapper_hash(
             {"x": CustomFeature},
             "7ff702d242612cbb83cbd1777aa79d2792fb2a341db5ea406cd9fd3f42543b9c",
         ),
+        (
+            TripleGenerator(),
+            ["x"],
+            {"triple": int},
+            "02b4c6bf98ffa011b7c62f3374f219f21796ece5b001d99e4c2f69edf0a94f4a",
+        ),
     ],
 )
 def test_udf_generator_hash(