From 09e15d29b432adb22adaff1a461a55e5a8ceef5d Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 12:52:09 -0300
Subject: [PATCH 01/17] Force flattened record according to provided flattened
 schema

---
 singer_sdk/helpers/_flattening.py | 11 ++++++---
 tests/core/test_flattening.py     | 40 +++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 3 deletions(-)
 create mode 100644 tests/core/test_flattening.py

diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index 77e3935b9..968a5f785 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -361,8 +361,8 @@ def _key_func(item: tuple[str, dict]) -> str:
 
 def flatten_record(
     record: dict,
-    flattened_schema: dict,
-    max_level: int,
+    flattened_schema: dict | None = None,
+    max_level: int | None = None,
     separator: str = "__",
 ) -> dict:
     """Flatten a record up to max_level.
@@ -376,6 +376,9 @@ def flatten_record(
     Returns:
         A flattened version of the record.
     """
+    assert (flattened_schema is not None) or (max_level is not None), "flattened_schema or max_level must be provided"
+    max_level = max_level or 0
+
     return _flatten_record(
         record_node=record,
         flattened_schema=flattened_schema,
@@ -415,7 +418,9 @@ def _flatten_record(
     items: list[tuple[str, t.Any]] = []
     for k, v in record_node.items():
         new_key = flatten_key(k, parent_key, separator)
-        if isinstance(v, collections.abc.MutableMapping) and level < max_level:
+        if (isinstance(v, MutableMapping) and
+                ((flattened_schema and new_key not in flattened_schema.get('properties', {})) or
+                 (not flattened_schema and level < max_level))):
             items.extend(
                 _flatten_record(
                     v,
diff --git a/tests/core/test_flattening.py b/tests/core/test_flattening.py
new file mode 100644
index 000000000..8b5f52de7
--- /dev/null
+++ b/tests/core/test_flattening.py
@@ -0,0 +1,40 @@
+from singer_sdk._flattening import flatten_record
+
+
+@pytest.mark.parametrize("flattened_schema, max_level, expected, expected_exception", [
+    pytest.param({
+        'properties': {
+            'key_1': {'type': ['null', 'integer']},
+            'key_2__key_3': {'type': ['null', 'string']},
+            'key_2__key_4': {'type': ['null', 'object']},
+        }
+    }, None, {'key_1': 1, 'key_2__key_3': 'value', 'key_2__key_4': '{"key_5": 1, "key_6": ["a", "b"]}'}, None,
+        id='flattened schema provided'),
+    pytest.param(None, 99,
+                 {'key_1': 1,
+                  'key_2__key_3': 'value',
+                  'key_2__key_4__key_5': 1,
+                  'key_2__key_4__key_6': '["a", "b"]'}, None,
+                 id='flattened schema not provided'),
+    pytest.param(None, None, None, AssertionError,
+                 id='no schema or max level provided'),
+])
+def test_flatten_record(flattened_schema, max_level, expected, expected_exception):
+    """Test flatten_record to obey the max_level and flattened_schema parameters."""
+    record = {
+        'key_1': 1,
+        'key_2': {
+            'key_3': 'value',
+            'key_4': {
+                'key_5': 1,
+                'key_6': ['a', 'b']
+            }
+        }
+    }
+    if expected_exception:
+        with pytest.raises(expected_exception):
+            flatten_record(record, max_level=max_level, flattened_schema=flattened_schema)
+    else:
+        result = flatten_record(record, max_level=max_level, flattened_schema=flattened_schema)
+        print(result)
+        assert expected == result

From 2fe8de32c7b6fad58fc6c36bd145c889f6825b81 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Thu, 15 Feb 2024 16:02:34 +0000
Subject: [PATCH 02/17] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 singer_sdk/helpers/_flattening.py | 12 ++---
 tests/core/test_flattening.py     | 75 +++++++++++++++++++------------
 2 files changed, 54 insertions(+), 33 deletions(-)

diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index 968a5f785..476d7561d 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -2,7 +2,6 @@
 
 from __future__ import annotations
 
-import collections
 import itertools
 import re
 import typing as t
@@ -376,7 +375,9 @@ def flatten_record(
     Returns:
         A flattened version of the record.
     """
-    assert (flattened_schema is not None) or (max_level is not None), "flattened_schema or max_level must be provided"
+    assert (flattened_schema is not None) or (
+        max_level is not None
+    ), "flattened_schema or max_level must be provided"
     max_level = max_level or 0
 
     return _flatten_record(
@@ -418,9 +419,10 @@ def _flatten_record(
     items: list[tuple[str, t.Any]] = []
     for k, v in record_node.items():
         new_key = flatten_key(k, parent_key, separator)
-        if (isinstance(v, MutableMapping) and
-                ((flattened_schema and new_key not in flattened_schema.get('properties', {})) or
-                 (not flattened_schema and level < max_level))):
+        if isinstance(v, MutableMapping) and (
+            (flattened_schema and new_key not in flattened_schema.get("properties", {}))
+            or (not flattened_schema and level < max_level)
+        ):
             items.extend(
                 _flatten_record(
                     v,
diff --git a/tests/core/test_flattening.py b/tests/core/test_flattening.py
index 8b5f52de7..4d6219f40 100644
--- a/tests/core/test_flattening.py
+++ b/tests/core/test_flattening.py
@@ -1,40 +1,59 @@
+from __future__ import annotations
+
 from singer_sdk._flattening import flatten_record
 
 
-@pytest.mark.parametrize("flattened_schema, max_level, expected, expected_exception", [
-    pytest.param({
-        'properties': {
-            'key_1': {'type': ['null', 'integer']},
-            'key_2__key_3': {'type': ['null', 'string']},
-            'key_2__key_4': {'type': ['null', 'object']},
-        }
-    }, None, {'key_1': 1, 'key_2__key_3': 'value', 'key_2__key_4': '{"key_5": 1, "key_6": ["a", "b"]}'}, None,
-        id='flattened schema provided'),
-    pytest.param(None, 99,
-                 {'key_1': 1,
-                  'key_2__key_3': 'value',
-                  'key_2__key_4__key_5': 1,
-                  'key_2__key_4__key_6': '["a", "b"]'}, None,
-                 id='flattened schema not provided'),
-    pytest.param(None, None, None, AssertionError,
-                 id='no schema or max level provided'),
-])
+@pytest.mark.parametrize(
+    "flattened_schema, max_level, expected, expected_exception",
+    [
+        pytest.param(
+            {
+                "properties": {
+                    "key_1": {"type": ["null", "integer"]},
+                    "key_2__key_3": {"type": ["null", "string"]},
+                    "key_2__key_4": {"type": ["null", "object"]},
+                }
+            },
+            None,
+            {
+                "key_1": 1,
+                "key_2__key_3": "value",
+                "key_2__key_4": '{"key_5": 1, "key_6": ["a", "b"]}',
+            },
+            None,
+            id="flattened schema provided",
+        ),
+        pytest.param(
+            None,
+            99,
+            {
+                "key_1": 1,
+                "key_2__key_3": "value",
+                "key_2__key_4__key_5": 1,
+                "key_2__key_4__key_6": '["a", "b"]',
+            },
+            None,
+            id="flattened schema not provided",
+        ),
+        pytest.param(
+            None, None, None, AssertionError, id="no schema or max level provided"
+        ),
+    ],
+)
 def test_flatten_record(flattened_schema, max_level, expected, expected_exception):
     """Test flatten_record to obey the max_level and flattened_schema parameters."""
     record = {
-        'key_1': 1,
-        'key_2': {
-            'key_3': 'value',
-            'key_4': {
-                'key_5': 1,
-                'key_6': ['a', 'b']
-            }
-        }
+        "key_1": 1,
+        "key_2": {"key_3": "value", "key_4": {"key_5": 1, "key_6": ["a", "b"]}},
     }
     if expected_exception:
         with pytest.raises(expected_exception):
-            flatten_record(record, max_level=max_level, flattened_schema=flattened_schema)
+            flatten_record(
+                record, max_level=max_level, flattened_schema=flattened_schema
+            )
     else:
-        result = flatten_record(record, max_level=max_level, flattened_schema=flattened_schema)
+        result = flatten_record(
+            record, max_level=max_level, flattened_schema=flattened_schema
+        )
         print(result)
         assert expected == result

From 0d945650896ca6bfc367d8d9030b5a3f35a98d06 Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 13:32:43 -0300
Subject: [PATCH 03/17] fix import

---
 tests/core/test_flattening.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tests/core/test_flattening.py b/tests/core/test_flattening.py
index 4d6219f40..3cb87c6ad 100644
--- a/tests/core/test_flattening.py
+++ b/tests/core/test_flattening.py
@@ -1,6 +1,8 @@
 from __future__ import annotations
 
-from singer_sdk._flattening import flatten_record
+import pytest
+
+from singer_sdk.helpers._flattening import flatten_record
 
 
 @pytest.mark.parametrize(

From 3a3532af534d6feb2fe5460b5e0b41bee7bc699b Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 13:34:00 -0300
Subject: [PATCH 04/17] fix

---
 singer_sdk/helpers/_flattening.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index 476d7561d..475233387 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -419,7 +419,7 @@ def _flatten_record(
     items: list[tuple[str, t.Any]] = []
     for k, v in record_node.items():
         new_key = flatten_key(k, parent_key, separator)
-        if isinstance(v, MutableMapping) and (
+        if isinstance(v, t.MutableMapping) and (
             (flattened_schema and new_key not in flattened_schema.get("properties", {}))
             or (not flattened_schema and level < max_level)
         ):

From dbdd0115fdef1cb58f8fb8a980a48c22b3865530 Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 13:37:06 -0300
Subject: [PATCH 05/17] revert collections change

---
 singer_sdk/helpers/_flattening.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index 475233387..18de38b68 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import collections
 import itertools
 import re
 import typing as t
@@ -419,7 +420,7 @@ def _flatten_record(
     items: list[tuple[str, t.Any]] = []
     for k, v in record_node.items():
         new_key = flatten_key(k, parent_key, separator)
-        if isinstance(v, t.MutableMapping) and (
+        if isinstance(v, collections.abc.MutableMapping) and (
             (flattened_schema and new_key not in flattened_schema.get("properties", {}))
             or (not flattened_schema and level < max_level)
         ):

From 2d39177ddabd4ee7aef5fc877214d94ac524b6b2 Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 13:52:27 -0300
Subject: [PATCH 06/17] ruff linter fixes

---
 singer_sdk/exceptions.py          | 4 ++++
 singer_sdk/helpers/_flattening.py | 7 ++++---
 tests/core/test_flattening.py     | 4 ++--
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/singer_sdk/exceptions.py b/singer_sdk/exceptions.py
index 03b06a7c0..4befe36ee 100644
--- a/singer_sdk/exceptions.py
+++ b/singer_sdk/exceptions.py
@@ -157,3 +157,7 @@ def __init__(self, error_message: str, record: dict) -> None:
         super().__init__(f"Record Message Validation Error: {error_message}")
         self.error_message = error_message
         self.record = record
+
+
+class InvalidFlatteningRecordsParameter(Exception):
+    """Raised when the flattening_records parameter is invalid."""
diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index 18de38b68..58ed68ab3 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -11,6 +11,8 @@
 import inflection
 import simplejson as json
 
+from exceptions import InvalidFlatteningRecordsParameter
+
 DEFAULT_FLATTENING_SEPARATOR = "__"
 
 
@@ -376,9 +378,8 @@ def flatten_record(
     Returns:
         A flattened version of the record.
     """
-    assert (flattened_schema is not None) or (
-        max_level is not None
-    ), "flattened_schema or max_level must be provided"
+    if (flattened_schema is not None) or (max_level is not None):
+        raise InvalidFlatteningRecordsParameter("flattened_schema or max_level must be provided")
     max_level = max_level or 0
 
     return _flatten_record(
diff --git a/tests/core/test_flattening.py b/tests/core/test_flattening.py
index 3cb87c6ad..f62afd02d 100644
--- a/tests/core/test_flattening.py
+++ b/tests/core/test_flattening.py
@@ -2,6 +2,7 @@
 
 import pytest
 
+from exceptions import InvalidFlatteningRecordsParameter
 from singer_sdk.helpers._flattening import flatten_record
 
 
@@ -38,7 +39,7 @@
             id="flattened schema not provided",
         ),
         pytest.param(
-            None, None, None, AssertionError, id="no schema or max level provided"
+            None, None, None, InvalidFlatteningRecordsParameter, id="no schema or max level provided"
         ),
     ],
 )
@@ -57,5 +58,4 @@ def test_flatten_record(flattened_schema, max_level, expected, expected_exceptio
         result = flatten_record(
             record, max_level=max_level, flattened_schema=flattened_schema
         )
-        print(result)
         assert expected == result

From f51aae8b01a61c6bf31fe2156db498521958c64c Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Thu, 15 Feb 2024 16:54:35 +0000
Subject: [PATCH 07/17] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 singer_sdk/helpers/_flattening.py | 4 +++-
 tests/core/test_flattening.py     | 6 +++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index 58ed68ab3..e188e59e1 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -379,7 +379,9 @@ def flatten_record(
         A flattened version of the record.
     """
     if (flattened_schema is not None) or (max_level is not None):
-        raise InvalidFlatteningRecordsParameter("flattened_schema or max_level must be provided")
+        raise InvalidFlatteningRecordsParameter(
+            "flattened_schema or max_level must be provided"
+        )
     max_level = max_level or 0
 
     return _flatten_record(
diff --git a/tests/core/test_flattening.py b/tests/core/test_flattening.py
index f62afd02d..37e63ff6b 100644
--- a/tests/core/test_flattening.py
+++ b/tests/core/test_flattening.py
@@ -39,7 +39,11 @@
             id="flattened schema not provided",
         ),
         pytest.param(
-            None, None, None, InvalidFlatteningRecordsParameter, id="no schema or max level provided"
+            None,
+            None,
+            None,
+            InvalidFlatteningRecordsParameter,
+            id="no schema or max level provided",
         ),
     ],
 )

From 77620d37931ab8aa8b869bf3e9e558a07b4dee4d Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 13:56:31 -0300
Subject: [PATCH 08/17] ruff linter fixes

---
 singer_sdk/helpers/_flattening.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index 58ed68ab3..7ddeb4bcb 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -379,7 +379,8 @@ def flatten_record(
         A flattened version of the record.
     """
     if (flattened_schema is not None) or (max_level is not None):
-        raise InvalidFlatteningRecordsParameter("flattened_schema or max_level must be provided")
+        msg = "flattened_schema or max_level must be provided"
+        raise InvalidFlatteningRecordsParameter(msg)
     max_level = max_level or 0
 
     return _flatten_record(

From 947b7a5f7dfff3952642578f657b3b6c55dd6560 Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 14:07:28 -0300
Subject: [PATCH 09/17] fix

---
 singer_sdk/helpers/_flattening.py | 2 +-
 tests/core/test_flattening.py     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index 7ddeb4bcb..34f2e4cc5 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -11,7 +11,7 @@
 import inflection
 import simplejson as json
 
-from exceptions import InvalidFlatteningRecordsParameter
+from singer_sdk.exceptions import InvalidFlatteningRecordsParameter
 
 DEFAULT_FLATTENING_SEPARATOR = "__"
 
diff --git a/tests/core/test_flattening.py b/tests/core/test_flattening.py
index 37e63ff6b..60d60ea55 100644
--- a/tests/core/test_flattening.py
+++ b/tests/core/test_flattening.py
@@ -2,7 +2,7 @@
 
 import pytest
 
-from exceptions import InvalidFlatteningRecordsParameter
+from singer_sdk.exceptions import InvalidFlatteningRecordsParameter
 from singer_sdk.helpers._flattening import flatten_record
 
 

From f31b49986393d23d53a1a42425a0a2de231aeaa1 Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 14:09:23 -0300
Subject: [PATCH 10/17] fix

---
 singer_sdk/helpers/_flattening.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index 34f2e4cc5..bb8a21fd1 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -378,7 +378,7 @@ def flatten_record(
     Returns:
         A flattened version of the record.
     """
-    if (flattened_schema is not None) or (max_level is not None):
+    if flattened_schema is None and max_level is None:
         msg = "flattened_schema or max_level must be provided"
         raise InvalidFlatteningRecordsParameter(msg)
     max_level = max_level or 0

From 2eb84ca0053d78aea90c225d90acf96241501437 Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 14:18:46 -0300
Subject: [PATCH 11/17] add test

---
 tests/core/test_flattening.py | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tests/core/test_flattening.py b/tests/core/test_flattening.py
index 60d60ea55..6d0af0820 100644
--- a/tests/core/test_flattening.py
+++ b/tests/core/test_flattening.py
@@ -38,6 +38,16 @@
             None,
             id="flattened schema not provided",
         ),
+        pytest.param(
+            None,
+            1,
+            {
+                'key_1': 1,
+                'key_2__key_3': 'value',
+                'key_2__key_4': '{"key_5": 1, "key_6": ["a", "b"]}'
+            },
+            None,
+            id='limited by max_level 2'),
         pytest.param(
             None,
             None,

From 2173ca17e0f5b43f4b827ec8567667e8f81127c5 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Thu, 15 Feb 2024 17:19:31 +0000
Subject: [PATCH 12/17] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 tests/core/test_flattening.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tests/core/test_flattening.py b/tests/core/test_flattening.py
index 6d0af0820..51a027ed6 100644
--- a/tests/core/test_flattening.py
+++ b/tests/core/test_flattening.py
@@ -42,12 +42,13 @@
             None,
             1,
             {
-                'key_1': 1,
-                'key_2__key_3': 'value',
-                'key_2__key_4': '{"key_5": 1, "key_6": ["a", "b"]}'
+                "key_1": 1,
+                "key_2__key_3": "value",
+                "key_2__key_4": '{"key_5": 1, "key_6": ["a", "b"]}',
             },
             None,
-            id='limited by max_level 2'),
+            id="limited by max_level 2",
+        ),
         pytest.param(
             None,
             None,

From 454758c9c9246dc3e7025920634fbd02e4a11c16 Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 17:21:03 -0300
Subject: [PATCH 13/17] removing None option for flatten schema and max level

---
 singer_sdk/exceptions.py          |  4 --
 singer_sdk/helpers/_flattening.py | 17 +++------
 tests/core/test_flattening.py     | 62 +++++++++++++++----------------
 3 files changed, 35 insertions(+), 48 deletions(-)

diff --git a/singer_sdk/exceptions.py b/singer_sdk/exceptions.py
index 4befe36ee..03b06a7c0 100644
--- a/singer_sdk/exceptions.py
+++ b/singer_sdk/exceptions.py
@@ -157,7 +157,3 @@ def __init__(self, error_message: str, record: dict) -> None:
         super().__init__(f"Record Message Validation Error: {error_message}")
         self.error_message = error_message
         self.record = record
-
-
-class InvalidFlatteningRecordsParameter(Exception):
-    """Raised when the flattening_records parameter is invalid."""
diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index bb8a21fd1..1ce64969b 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -11,8 +11,6 @@
 import inflection
 import simplejson as json
 
-from singer_sdk.exceptions import InvalidFlatteningRecordsParameter
-
 DEFAULT_FLATTENING_SEPARATOR = "__"
 
 
@@ -363,8 +361,8 @@ def _key_func(item: tuple[str, dict]) -> str:
 
 def flatten_record(
     record: dict,
-    flattened_schema: dict | None = None,
-    max_level: int | None = None,
+    flattened_schema: dict,
+    max_level: int,
     separator: str = "__",
 ) -> dict:
     """Flatten a record up to max_level.
@@ -378,11 +376,6 @@ def flatten_record(
     Returns:
         A flattened version of the record.
     """
-    if flattened_schema is None and max_level is None:
-        msg = "flattened_schema or max_level must be provided"
-        raise InvalidFlatteningRecordsParameter(msg)
-    max_level = max_level or 0
-
     return _flatten_record(
         record_node=record,
         flattened_schema=flattened_schema,
@@ -394,7 +387,7 @@ def flatten_record(
 def _flatten_record(
     record_node: t.MutableMapping[t.Any, t.Any],
     *,
-    flattened_schema: dict | None = None,
+    flattened_schema: dict,
     parent_key: list[str] | None = None,
     separator: str = "__",
     level: int = 0,
@@ -423,8 +416,8 @@ def _flatten_record(
     for k, v in record_node.items():
         new_key = flatten_key(k, parent_key, separator)
         if isinstance(v, collections.abc.MutableMapping) and (
-            (flattened_schema and new_key not in flattened_schema.get("properties", {}))
-            or (not flattened_schema and level < max_level)
+            (new_key not in flattened_schema.get("properties", {}))
+            and (level < max_level)
         ):
             items.extend(
                 _flatten_record(
diff --git a/tests/core/test_flattening.py b/tests/core/test_flattening.py
index 6d0af0820..8e19a4d3e 100644
--- a/tests/core/test_flattening.py
+++ b/tests/core/test_flattening.py
@@ -2,12 +2,11 @@
 
 import pytest
 
-from singer_sdk.exceptions import InvalidFlatteningRecordsParameter
 from singer_sdk.helpers._flattening import flatten_record
 
 
 @pytest.mark.parametrize(
-    "flattened_schema, max_level, expected, expected_exception",
+    "flattened_schema, max_level, expected",
     [
         pytest.param(
             {
@@ -17,17 +16,23 @@
                     "key_2__key_4": {"type": ["null", "object"]},
                 }
             },
-            None,
+            99,
             {
                 "key_1": 1,
                 "key_2__key_3": "value",
                 "key_2__key_4": '{"key_5": 1, "key_6": ["a", "b"]}',
             },
-            None,
-            id="flattened schema provided",
+            id="flattened schema limiting the max level",
         ),
         pytest.param(
-            None,
+            {
+                "properties": {
+                    "key_1": {"type": ["null", "integer"]},
+                    "key_2__key_3": {"type": ["null", "string"]},
+                    "key_2__key_4__key_5": {"type": ["null", "integer"]},
+                    "key_2__key_4__key_6": {"type": ["null", "array"]},
+                }
+            },
             99,
             {
                 "key_1": 1,
@@ -35,41 +40,34 @@
                 "key_2__key_4__key_5": 1,
                 "key_2__key_4__key_6": '["a", "b"]',
             },
-            None,
-            id="flattened schema not provided",
+            id="flattened schema not limiting the max level",
         ),
         pytest.param(
-            None,
+            {
+                "properties": {
+                    "key_1": {"type": ["null", "integer"]},
+                    "key_2__key_3": {"type": ["null", "string"]},
+                    "key_2__key_4__key_5": {"type": ["null", "integer"]},
+                    "key_2__key_4__key_6": {"type": ["null", "array"]},
+                }
+            },
             1,
             {
-                'key_1': 1,
-                'key_2__key_3': 'value',
-                'key_2__key_4': '{"key_5": 1, "key_6": ["a", "b"]}'
+                "key_1": 1,
+                "key_2__key_3": "value",
+                "key_2__key_4": '{"key_5": 1, "key_6": ["a", "b"]}',
             },
-            None,
-            id='limited by max_level 2'),
-        pytest.param(
-            None,
-            None,
-            None,
-            InvalidFlatteningRecordsParameter,
-            id="no schema or max level provided",
-        ),
+            id="max level limiting flattened schema")
     ],
 )
-def test_flatten_record(flattened_schema, max_level, expected, expected_exception):
+def test_flatten_record(flattened_schema, max_level, expected):
     """Test flatten_record to obey the max_level and flattened_schema parameters."""
     record = {
         "key_1": 1,
         "key_2": {"key_3": "value", "key_4": {"key_5": 1, "key_6": ["a", "b"]}},
     }
-    if expected_exception:
-        with pytest.raises(expected_exception):
-            flatten_record(
-                record, max_level=max_level, flattened_schema=flattened_schema
-            )
-    else:
-        result = flatten_record(
-            record, max_level=max_level, flattened_schema=flattened_schema
-        )
-        assert expected == result
+
+    result = flatten_record(
+        record, max_level=max_level, flattened_schema=flattened_schema
+    )
+    assert expected == result

From f6988977c8d059fc38cda3bd14fab6c637e7ceff Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Thu, 15 Feb 2024 20:22:51 +0000
Subject: [PATCH 14/17] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 tests/core/test_flattening.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tests/core/test_flattening.py b/tests/core/test_flattening.py
index 8e19a4d3e..73169eab3 100644
--- a/tests/core/test_flattening.py
+++ b/tests/core/test_flattening.py
@@ -57,7 +57,8 @@
                 "key_2__key_3": "value",
                 "key_2__key_4": '{"key_5": 1, "key_6": ["a", "b"]}',
             },
-            id="max level limiting flattened schema")
+            id="max level limiting flattened schema",
+        ),
     ],
 )
 def test_flatten_record(flattened_schema, max_level, expected):

From 35e191be8e72f2b7f3ada6332e29e48fa5dcd5ea Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 17:23:22 -0300
Subject: [PATCH 15/17] revert typing

---
 singer_sdk/helpers/_flattening.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index 1ce64969b..580a31b16 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -387,7 +387,7 @@ def flatten_record(
 def _flatten_record(
     record_node: t.MutableMapping[t.Any, t.Any],
     *,
-    flattened_schema: dict,
+    flattened_schema: dict | None = None,
     parent_key: list[str] | None = None,
     separator: str = "__",
     level: int = 0,

From 73b881b08ee5e3bf354b823b9d5a8f44a6ddd65b Mon Sep 17 00:00:00 2001
From: Joao Amaral <7281460+joaopamaral@users.noreply.github.com>
Date: Thu, 15 Feb 2024 17:28:40 -0300
Subject: [PATCH 16/17] fix check

---
 singer_sdk/helpers/_flattening.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index 580a31b16..d5bc4afff 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -416,7 +416,7 @@ def _flatten_record(
     for k, v in record_node.items():
         new_key = flatten_key(k, parent_key, separator)
         if isinstance(v, collections.abc.MutableMapping) and (
-            (new_key not in flattened_schema.get("properties", {}))
+            (flattened_schema and new_key not in flattened_schema.get("properties", {}))
             and (level < max_level)
         ):
             items.extend(

From 938d15e69196ea8af3b7105bce66772fb2eeafc9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Edgar=20Ram=C3=ADrez-Mondrag=C3=B3n?= <edgarrm358@gmail.com>
Date: Thu, 15 Feb 2024 16:24:02 -0600
Subject: [PATCH 17/17] Add a short comment

---
 singer_sdk/helpers/_flattening.py | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/singer_sdk/helpers/_flattening.py b/singer_sdk/helpers/_flattening.py
index d5bc4afff..2a3e194d0 100644
--- a/singer_sdk/helpers/_flattening.py
+++ b/singer_sdk/helpers/_flattening.py
@@ -415,8 +415,12 @@ def _flatten_record(
     items: list[tuple[str, t.Any]] = []
     for k, v in record_node.items():
         new_key = flatten_key(k, parent_key, separator)
-        if isinstance(v, collections.abc.MutableMapping) and (
-            (flattened_schema and new_key not in flattened_schema.get("properties", {}))
+        # If the value is a dictionary, and the key is not in the schema, and the
+        # level is less than the max level, then we should continue to flatten.
+        if (
+            isinstance(v, collections.abc.MutableMapping)
+            and flattened_schema
+            and new_key not in flattened_schema.get("properties", {})
             and (level < max_level)
         ):
             items.extend(