diff --git a/src/resdk/tables/base.py b/src/resdk/tables/base.py
index aa2399c..4f9c55b 100644
--- a/src/resdk/tables/base.py
+++ b/src/resdk/tables/base.py
@@ -14,9 +14,11 @@ import abc
 import asyncio
 import json
 import os
+import warnings
+from collections import Counter
 from functools import lru_cache
 from io import BytesIO
-from typing import Callable, List, Optional
+from typing import Callable, Dict, List, Optional
 from urllib.parse import urljoin
 
 import aiohttp
@@ -128,10 +130,23 @@ class BaseTables(abc.ABC):
 
         :return: list od Sample objects
         """
-        sample_ids = [d.sample.id for d in self._data]
-        return list(
-            self.collection.samples.filter(id__in=sample_ids, fields=SAMPLE_FIELDS)
-        )
+        sample_ids = set([d.sample.id for d in self._data])
+
+        query = self.collection.samples.filter(fields=SAMPLE_FIELDS)
+        return [s for s in query if s.id in sample_ids]
+
+    @property
+    def readable_index(self) -> Dict[int, str]:
+        """Get mapping from index values to readable names."""
+        names = [s.name for s in self._samples]
+        if len(set(names)) != len(names):
+            repeated = [item for item, count in Counter(names).items() if count > 1]
+            repeated = ", ".join(repeated)
+            warnings.warn(
+                f"The following names are repeated in index: {repeated}", UserWarning
+            )
+
+        return {s.id: s.name for s in self._samples}
 
     @property
     @lru_cache()
@@ -240,10 +255,10 @@ class BaseTables(abc.ABC):
     def _get_descriptors(self) -> pd.DataFrame:
         descriptors = []
         for sample in self._samples:
-            sample.descriptor["sample_name"] = sample.name
+            sample.descriptor["sample_id"] = sample.id
             descriptors.append(sample.descriptor)
 
-        df = pd.json_normalize(descriptors).set_index("sample_name")
+        df = pd.json_normalize(descriptors).set_index("sample_id")
 
         # Keep only numeric / string types:
         column_types = {}
@@ -272,15 +287,13 @@ class BaseTables(abc.ABC):
         return df
 
     def _get_relations(self) -> pd.DataFrame:
-        relations = pd.DataFrame(index=[s.name for s in self._samples])
-        relations.index.name = "sample_name"
-
-        id_to_name = {s.id: s.name for s in self._samples}
+        relations = pd.DataFrame(index=[s.id for s in self._samples])
+        relations.index.name = "sample_id"
 
         for relation in self.collection.relations.filter():
             # Only consider relations that include only samples in self.samples
             relation_entities_ids = set([p["entity"] for p in relation.partitions])
-            if not relation_entities_ids.issubset({d.sample.id for d in self._data}):
+            if not relation_entities_ids.issubset({s.id for s in self._samples}):
                 pass
 
             relations[relation.category] = pd.Series(
@@ -296,9 +309,7 @@ class BaseTables(abc.ABC):
                 elif partition["position"]:
                     value = partition["position"]
 
-                sample_name = id_to_name.get(partition["entity"], None)
-                if sample_name:
-                    relations[relation.category][sample_name] = value
+                relations[relation.category][partition["entity"]] = value
 
         return relations
 
@@ -338,39 +349,40 @@ class BaseTables(abc.ABC):
                 return pd.DataFrame()
 
         if "mS#Sample ID" in df.columns:
-            mapping = {s.id: s.name for s in self._samples}
-            df["sample_name"] = [mapping[value] for value in df["mS#Sample ID"]]
-            df = df.drop(columns=["mS#Sample ID"])
+            df = df.rename(columns={"mS#Sample ID": "sample_id"})
         elif "mS#Sample slug" in df.columns:
-            mapping = {s.slug: s.name for s in self._samples}
-            df["sample_name"] = [mapping[value] for value in df["mS#Sample slug"]]
+            mapping = {s.slug: s.id for s in self._samples}
+            df["sample_id"] = [mapping[value] for value in df["mS#Sample slug"]]
             df = df.drop(columns=["mS#Sample slug"])
         elif "mS#Sample name" in df.columns:
-            df = df.rename(columns={"mS#Sample name": "sample_name"})
+            mapping = {s.name: s.id for s in self._samples}
+            if len(mapping) != len(self._samples):
+                raise ValueError(
+                    "Duplicate sample names. Cannot map orange table data to other matadata"
+                )
+            df["sample_id"] = [mapping[value] for value in df["mS#Sample name"]]
+            df = df.drop(columns=["mS#Sample name"])
 
-        return df.set_index("sample_name")
+        return df.set_index("sample_id")
 
     def _download_metadata(self) -> pd.DataFrame:
         """Download samples metadata and transform into table."""
-        meta = pd.DataFrame(None, index=[s.name for s in self._samples])
+        meta = pd.DataFrame(None, index=[s.id for s in self._samples])
 
         # Add descriptors metadata
         descriptors = self._get_descriptors()
-        meta = meta.merge(descriptors, how="right", left_index=True, right_index=True)
+        meta = meta.merge(descriptors, how="left", left_index=True, right_index=True)
 
         # Add relations metadata
         relations = self._get_relations()
-        how = "outer" if len(meta.columns) else "right"
-        meta = meta.merge(relations, how=how, left_index=True, right_index=True)
+        meta = meta.merge(relations, how="left", left_index=True, right_index=True)
 
         # Add Orange clinical metadata
         orange_data = self._get_orange_data()
-        if not orange_data.empty:
-            how = "right" if meta.columns.empty else "outer"
-            meta = meta.merge(orange_data, how=how, left_index=True, right_index=True)
+        meta = meta.merge(orange_data, how="left", left_index=True, right_index=True)
 
         meta = meta.sort_index()
-        meta.index.name = "sample_name"
+        meta.index.name = "sample_id"
 
         return meta
 
@@ -397,17 +409,17 @@ class BaseTables(abc.ABC):
         return json.loads(response.content.decode("utf-8"))
 
     @abc.abstractmethod
-    def _parse_file(self, file_obj, sample_name, data_type):
+    def _parse_file(self, file_obj, sample_id, data_type):
         """Parse file object and return a one DataFrame line."""
         pass
 
-    async def _download_file(self, url, session, sample_name, data_type):
+    async def _download_file(self, url, session, sample_id, data_type):
         async with session.get(url) as response:
             response.raise_for_status()
             with BytesIO() as f:
                 f.write(await response.content.read())
                 f.seek(0)
-                sample_data = self._parse_file(f, sample_name, data_type)
+                sample_data = self._parse_file(f, sample_id, data_type)
         return sample_data
 
     async def _download_data(self, data_type: str) -> pd.DataFrame:
@@ -439,23 +451,22 @@ class BaseTables(abc.ABC):
         ):
             data_subset = self._data[i : i + EXP_ASYNC_CHUNK_SIZE]
 
-            # Mapping from file uri to sample name
-            uri_to_name = {
-                self._get_data_uri(d, data_type): d._original_values["entity"]["name"]
-                for d in data_subset
+            # Mapping from file uri to sample id
+            uri_to_id = {
+                self._get_data_uri(d, data_type): d.sample.id for d in data_subset
             }
 
-            source_urls = self._get_data_urls(uri_to_name.keys())
-            urls_names = [(url, uri_to_name[uri]) for uri, url in source_urls.items()]
+            source_urls = self._get_data_urls(uri_to_id.keys())
+            urls_ids = [(url, uri_to_id[uri]) for uri, url in source_urls.items()]
 
             async with aiohttp.ClientSession() as session:
                 futures = [
-                    self._download_file(url, session, name, data_type)
-                    for url, name in urls_names
+                    self._download_file(url, session, id_, data_type)
+                    for url, id_ in urls_ids
                 ]
                 data = await asyncio.gather(*futures)
                 samples_data.extend(data)
 
         df = pd.concat(samples_data, axis=1).T.sort_index().sort_index(axis=1)
-        df.index.name = "sample_name"
+        df.index.name = "sample_id"
         return df
diff --git a/src/resdk/tables/methylation.py b/src/resdk/tables/methylation.py
index e090e83..37ed61c 100644
--- a/src/resdk/tables/methylation.py
+++ b/src/resdk/tables/methylation.py
@@ -99,7 +99,7 @@ class MethylationTables(BaseTables):
         cache_file = f"{self.collection.slug}_{data_type}_{version}.pickle"
         return os.path.join(self.cache_dir, cache_file)
 
-    def _parse_file(self, file_obj, sample_name, data_type):
+    def _parse_file(self, file_obj, sample_id, data_type):
         """Parse file object and return one DataFrame line."""
         sample_data = pd.read_csv(
             file_obj,
@@ -108,5 +108,5 @@ class MethylationTables(BaseTables):
             usecols=["probe_ids", data_type],
             index_col="probe_ids",
         )[data_type]
-        sample_data.name = sample_name
+        sample_data.name = sample_id
         return sample_data
diff --git a/src/resdk/tables/rna.py b/src/resdk/tables/rna.py
index 287bae8..551d896 100644
--- a/src/resdk/tables/rna.py
+++ b/src/resdk/tables/rna.py
@@ -11,6 +11,7 @@ RNATables
 
 """
 import os
+import warnings
 from functools import lru_cache
 from typing import Callable, Dict, List, Optional
 
@@ -154,7 +155,7 @@ class RNATables(BaseTables):
 
     @property
     @lru_cache()
-    def id_to_symbol(self) -> Dict[str, str]:
+    def readable_columns(self) -> Dict[str, str]:
         """Map of source gene ids to symbols.
 
         This also gets fetched only once and then cached in memory and
@@ -179,6 +180,17 @@ class RNATables(BaseTables):
 
         return self._mapping(self.gene_ids, source, species)
 
+    @property
+    @lru_cache()
+    def id_to_symbol(self) -> Dict[str, str]:
+        """Map of source gene ids to symbols."""
+        warnings.warn(
+            "Attribute `id_to_symbol` will be removed in Q1 of 2022. "
+            "Use `readable_columns` instead.",
+            DeprecationWarning,
+        )
+        return self.readable_columns
+
     @property
     @lru_cache()
     def _data(self) -> List[Data]:
@@ -210,11 +222,11 @@ class RNATables(BaseTables):
         cache_file = f"{self.collection.slug}_{data_type}_{self.expression_source}_{self.expression_process_slug}_{version}.pickle"
         return os.path.join(self.cache_dir, cache_file)
 
-    def _parse_file(self, file_obj, sample_name, data_type):
+    def _parse_file(self, file_obj, sample_id, data_type):
         """Parse file object and return a one DataFrame line."""
         sample_data = pd.read_csv(file_obj, sep="\t", compression="gzip")
         sample_data = sample_data.set_index("Gene")["Expression"]
-        sample_data.name = sample_name
+        sample_data.name = sample_id
         return sample_data
 
     async def _download_data(self, data_type: str) -> pd.DataFrame:

diff --git a/tests/functional/tables/e2e_tables.py b/tests/functional/tables/e2e_tables.py
index f6ad507..2fa12ad 100644
--- a/tests/functional/tables/e2e_tables.py
+++ b/tests/functional/tables/e2e_tables.py
@@ -27,21 +27,21 @@ class TestTables(BaseResdkFunctionalTest):
 
     def test_meta(self):
         self.assertEqual(self.ct.meta.shape, (8, 9))
-        self.assertIn("Copy of SUM149_JQ1_12H_R1", self.ct.meta.index)
+        self.assertIn(39000, self.ct.meta.index)
         self.assertIn("general.species", self.ct.meta.columns)
 
     def test_rc(self):
         self.assertEqual(self.ct.rc.shape, (8, 58487))
-        self.assertIn("Copy of SUM149_JQ1_12H_R1", self.ct.rc.index)
+        self.assertIn(39000, self.ct.rc.index)
         self.assertIn("ENSG00000000003", self.ct.rc.columns)
-        self.assertEqual(self.ct.rc.iloc[0, 0], 1580)
+        self.assertEqual(self.ct.rc.iloc[0, 0], 792)
         self.assertIsInstance(self.ct.rc.iloc[0, 0], np.int64)
 
     def test_exp(self):
         self.assertEqual(self.ct.exp.shape, (8, 58487))
-        self.assertIn("Copy of SUM149_JQ1_12H_R1", self.ct.exp.index)
+        self.assertIn(39000, self.ct.exp.index)
         self.assertIn("ENSG00000000003", self.ct.exp.columns)
-        self.assertAlmostEqual(self.ct.exp.iloc[0, 0], 32.924003, places=3)
+        self.assertAlmostEqual(self.ct.exp.iloc[0, 0], 19.447467, places=3)
         self.assertIsInstance(self.ct.exp.iloc[0, 0], np.float64)
 
     def test_consistent_index(self):
diff --git a/tests/unit/test_tables.py b/tests/unit/test_tables.py
index e14d5f6..fad2bc3 100644
--- a/tests/unit/test_tables.py
+++ b/tests/unit/test_tables.py
@@ -28,6 +28,7 @@ class TestTables(unittest.TestCase):
 
         self.data = MagicMock()
         self.data.id = 12345
+        self.data.sample.id = self.sample.id
         self.data.process.slug = "process-slug"
         self.data.output.__getitem__.side_effect = {
             "species": "Homo sapiens",
@@ -58,9 +59,7 @@ class TestTables(unittest.TestCase):
             {"id": 1, "entity": 123, "position": None, "label": "L1"}
         ]
         self.collection.relations.filter = self.web_request([self.relation])
-        self.metadata_df = pd.DataFrame(
-            [[0], [1], [4]], index=["0", "1", "2"], columns=["PFS"]
-        )
+        self.metadata_df = pd.DataFrame([[0]], index=[123], columns=["PFS"])
 
         self.expressions_df = pd.DataFrame(
             [[0, 1, 2], [1, 2, 3], [2, 3, 4]],
@@ -288,8 +287,8 @@ class TestTables(unittest.TestCase):
         ct = RNATables(self.collection)
         descriptors = ct._get_descriptors()
 
-        expected = pd.DataFrame([1], columns=["PFS"], index=["Sample123"], dtype=float)
-        expected.index.name = "sample_name"
+        expected = pd.DataFrame([1], columns=["PFS"], index=[123], dtype=float)
+        expected.index.name = "sample_id"
 
         assert_frame_equal(descriptors, expected)
 
@@ -297,8 +296,8 @@ class TestTables(unittest.TestCase):
         ct = RNATables(self.collection)
         relations = ct._get_relations()
 
-        expected = pd.DataFrame(["L1"], columns=["Category"], index=["Sample123"])
-        expected.index.name = "sample_name"
+        expected = pd.DataFrame(["L1"], columns=["Category"], index=[123])
+        expected.index.name = "sample_id"
 
         assert_frame_equal(relations, expected)
 
@@ -318,32 +317,32 @@ class TestTables(unittest.TestCase):
         ct = RNATables(self.collection)
         orange_data = ct._get_orange_data()
 
-        expected = pd.DataFrame([42], columns=["Col1"], index=["Sample123"])
-        expected.index.name = "sample_name"
+        expected = pd.DataFrame([42], columns=["Col1"], index=[123])
+        expected.index.name = "sample_id"
 
         assert_frame_equal(orange_data, expected)
 
     @patch.object(RNATables, "_get_descriptors")
     @patch.object(RNATables, "_get_relations")
     @patch.object(RNATables, "_get_orange_data")
-    def test_download_metadata(self, descriptors_mock, relations_mock, orange_mock):
+    def test_download_metadata(self, orange_mock, relations_mock, descriptors_mock):
         descriptors_mock.return_value = self.metadata_df
         relations_mock.return_value = pd.DataFrame(
-            [["A"], ["B"], ["C"]], index=["0", "1", "2"], columns=["Replicate"]
+            [["A"]], index=[123], columns=["Replicate"]
         )
         orange_mock.return_value = pd.DataFrame(
-            [["X"], ["Y"], ["Z"]], index=["0", "1", "2"], columns=["Clinical"]
+            [["X"]], index=[123], columns=["Clinical"]
         )
 
         ct = RNATables(self.collection)
         meta = ct._download_metadata()
 
-        expected_content = [["X", "A", 0], ["Y", "B", 1], ["Z", "C", 4]]
-        expected_columns = ["Clinical", "Replicate", "PFS"]
+        expected_content = [[0, "A", "X"]]
+        expected_columns = ["PFS", "Replicate", "Clinical"]
         expected_meta = pd.DataFrame(
-            expected_content, columns=expected_columns, index=["0", "1", "2"]
+            expected_content, columns=expected_columns, index=[123]
         )
-        expected_meta.index.name = "sample_name"
+        expected_meta.index.name = "sample_id"
 
         assert_frame_equal(meta, expected_meta)
 

CollectionTables unable to fatch metadata from large collection
During downloading of metadata from a large collection (it has 1220 samples) you get the following exception:
```
/home/robert/git/resolwe-bio-py/venv/bin/python /home/robert/git/resolwe-bio-py/foo.py
Traceback (most recent call last):
  File "/home/robert/git/resolwe-bio-py/src/resdk/exceptions.py", line 32, in wrapper
    return func(*args, **kwargs)
  File "/home/robert/git/resolwe-bio-py/venv/lib/python3.8/site-packages/slumber/__init__.py", line 155, in get
    resp = self._request("GET", params=kwargs)
  File "/home/robert/git/resolwe-bio-py/venv/lib/python3.8/site-packages/slumber/__init__.py", line 101, in _request
    raise exception_class("Client Error %s: %s" % (resp.status_code, url), response=resp, content=resp.content)
slumber.exceptions.HttpClientError: Client Error 414: https://app.genialis.com/api/sample

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/robert/git/resolwe-bio-py/foo.py", line 6, in <module>
    meta = col_tab.meta
  File "/home/robert/git/resolwe-bio-py/src/resdk/collection_tables.py", line 176, in meta
    return self._load_fetch(META)
  File "/home/robert/git/resolwe-bio-py/src/resdk/collection_tables.py", line 354, in _load_fetch
    data = self._download_metadata()
  File "/home/robert/git/resolwe-bio-py/src/resdk/collection_tables.py", line 488, in _download_metadata
    meta = pd.DataFrame(None, index=[s.name for s in self._samples])
  File "/home/robert/git/resolwe-bio-py/src/resdk/collection_tables.py", line 251, in _samples
    return list(
  File "/home/robert/git/resolwe-bio-py/src/resdk/query.py", line 145, in __len__
    return self.count()
  File "/home/robert/git/resolwe-bio-py/src/resdk/query.py", line 222, in count
    count_query._fetch()
  File "/home/robert/git/resolwe-bio-py/src/resdk/query.py", line 196, in _fetch
    items = self.api.get(**filters)
  File "/home/robert/git/resolwe-bio-py/src/resdk/exceptions.py", line 34, in wrapper
    raise ResolweServerError(exception.content)
resdk.exceptions.ResolweServerError: b'<html>\r\n<head><title>414 Request-URI Too Large</title></head>\r\n<body>\r\n<center><h1>414 Request-URI Too Large</h1></center>\r\n<hr><center>nginx</center>\r\n</body>\r\n</html>\r\n'
```
The root of the problem is in `_samples` where we filter samples by ids which results in a large `id__in` filter/argument and consequently, a large URL send to the server. 
tests/unit/test_tables.py::TestTables::test_download_metadata tests/unit/test_tables.py::TestTables::test_get_descriptors tests/unit/test_tables.py::TestTables::test_get_orange_data tests/unit/test_tables.py::TestTables::test_get_relations
tests/unit/test_tables.py::TestTables::test_clear_cache tests/unit/test_tables.py::TestTables::test_data_version tests/unit/test_tables.py::TestTables::test_download_mapping tests/unit/test_tables.py::TestTables::test_exp tests/unit/test_tables.py::TestTables::test_get_data_uri tests/unit/test_tables.py::TestTables::test_get_orange_object tests/unit/test_tables.py::TestTables::test_heterogeneous_collections tests/unit/test_tables.py::TestTables::test_id_to_symbol tests/unit/test_tables.py::TestTables::test_init tests/unit/test_tables.py::TestTables::test_load_fetch tests/unit/test_tables.py::TestTables::test_mapping tests/unit/test_tables.py::TestTables::test_meta tests/unit/test_tables.py::TestTables::test_metadata_version tests/unit/test_tables.py::TestTables::test_rc