Max recursion depth param

README.md

@@ -90,6 +90,22 @@ result = item.to_dict(exclude_values=(None, True, ''))
 ```
 **Note** that `exclude_values` works with hashable values only. It filters values after serialization, so it works with nested dictionaries and models as well.
 
+If you want to control the maximum depth for relationship recursion:
+```python
+# Limit to one level of nesting (prevents infinite recursion)
+result = item.to_dict(max_serialization_depth=1)
+
+# Disable relationship serialization entirely
+result = item.to_dict(max_serialization_depth=0)
+
+# Set default for all instances of a model
+class SomeModel(db.Model, SerializerMixin):
+    max_serialization_depth = 1  # Only serialize direct relationships
+    ...
+```
+By default, `max_serialization_depth` is `math.inf` (unlimited), maintaining backward compatibility.
+See [Max recursion](#Max-recursion) for more details.
+
 If you want to define schema for all instances of particular SQLAlchemy model,
 add serialize properties to model definition:
 ```python
@@ -392,7 +408,23 @@ response = serialize_collection(Category.query.all(), **some_params)
 ## Max recursion
 If you've faced with **maximum recursion depth exceeded** exception,
 most likely the serializer have found instance of the same class somewhere among model's relationships.
-Especially if you use backrefs. In this case you need to tell it where to stop like below:
+Especially if you use backrefs. 
+
+**Solution 1: Use `max_serialization_depth` (Recommended)**
+The easiest way to prevent infinite recursion is to set a maximum depth:
+```python
+# Per-call limit
+user.to_dict(max_serialization_depth=1)  # Only serialize direct relationships
+
+# Model-level default
+class User(Base, SerializerMixin):
+    max_serialization_depth = 1  # Prevent recursion for all instances
+    ...
+    related_models = relationship("RelatedModel", backref='user')
+```
+
+**Solution 2: Use rules to exclude specific relationships**
+You can also use rules to tell the serializer where to stop:
 ```python
 class User(Base, SerializerMixin):
     __tablename__ = 'users'

sqlalchemy_serializer/serializer.py

@@ -1,5 +1,6 @@
 import inspect
 import logging
+import math
 import typing as t
 import uuid
 from collections import namedtuple
@@ -57,6 +58,9 @@ class SerializerMixin:
     # Serialize fields of the model defined as @property automatically
     auto_serialize_properties: bool = False
 
+    # Maximum depth for relationship recursion (default: unlimited)
+    max_serialization_depth: float = math.inf
+
     def get_tzinfo(self):
         """Callback to make serializer aware of user's timezone. Should be redefined if needed
         Example:
@@ -77,6 +81,7 @@ def to_dict(
         decimal_format=None,
         serialize_types=None,
         exclude_values=None,
+        max_serialization_depth=None,
     ):
         """Returns SQLAlchemy model's data in JSON compatible format
 
@@ -93,6 +98,8 @@ def to_dict(
         :param serialize_types:
         :param tzinfo: datetime.tzinfo converts datetimes to local user timezone
         :param exclude_values: iterable of hashable values to exclude from serialized output
+        :param max_serialization_depth: maximum depth for relationship recursion
+            (default: unlimited)
         :return: data: dict
         """
         s = Serializer(
@@ -103,13 +110,18 @@ def to_dict(
             tzinfo=tzinfo or self.get_tzinfo(),
             serialize_types=serialize_types or self.serialize_types,
             exclude_values=exclude_values or self.exclude_values,
+            max_serialization_depth=(
+                max_serialization_depth
+                if max_serialization_depth is not None
+                else self.max_serialization_depth
+            ),
         )
         return s(self, only=only, extend=rules)
 
 
 Options = namedtuple(
     "Options",
-    "date_format datetime_format time_format decimal_format tzinfo serialize_types exclude_values",  # noqa: E501
+    "date_format datetime_format time_format decimal_format tzinfo serialize_types exclude_values max_serialization_depth",  # noqa: E501
 )
 
 
@@ -139,6 +151,7 @@ def __init__(self, **kwargs):
             "tzinfo": kwargs.get("tzinfo"),
             "serialize_types": kwargs.get("serialize_types", ()),
             "exclude_values": exclude_values_set,
+            "max_serialization_depth": kwargs.get("max_serialization_depth", math.inf),
         }
         self.set_options(Options(**options_kwargs))
         self.init_callbacks()
@@ -271,6 +284,14 @@ def serialize_with_fork(self, value, key):
         """Serialize value with a forked serializer"""
         serializer = self
         if self.is_forkable(value):
+            # Check depth limit before forking
+            if self.serialization_depth >= self.opts.max_serialization_depth:
+                logger.debug(
+                    "Max serialization depth reached at depth:%s for key:%s",
+                    self.serialization_depth,
+                    key,
+                )
+                return _UNSPECIFIED
             serializer = self.fork(key=key)
 
         return serializer.apply_callback(value)

tests/test_max_serialization_depth.py

@@ -0,0 +1,163 @@
+import math
+
+import pytest
+
+from .models import FlatModel, NestedModel, RecursiveModel
+
+
+@pytest.fixture
+def three_level_recursive_model(get_instance):
+    """Create a 3-level recursive model structure: root -> child -> grandchild"""
+    root = get_instance(RecursiveModel)
+    child_full = get_instance(RecursiveModel, parent_id=root.id)
+    get_instance(RecursiveModel, parent_id=child_full.id)
+    return root
+
+
+def test_default_unlimited_depth(three_level_recursive_model):
+    """Test that default behavior maintains unlimited depth (backward compatible)"""
+    # Default should be unlimited (math.inf)
+    data = three_level_recursive_model.to_dict()
+
+    assert "children" in data
+    assert "children" in data["children"][0]
+    assert "children" in data["children"][0]["children"][0]
+
+    assert "name" in data
+    assert "name" in data["children"][0]
+    assert "name" in data["children"][0]["children"][0]
+
+
+def test_model_level_max_depth(three_level_recursive_model):
+    """Test max_serialization_depth set on model class"""
+    # Set max depth to 1 (only serialize direct children, not grandchildren)
+    three_level_recursive_model.max_serialization_depth = 1
+    data = three_level_recursive_model.to_dict()
+
+    assert "children" in data
+    # But grandchildren should not be serialized
+    assert "children" not in data["children"][0]
+
+    assert "name" in data
+    assert "name" in data["children"][0]  # Name is still there
+
+
+def test_per_call_max_depth(three_level_recursive_model):
+    """Test max_serialization_depth passed to to_dict() method"""
+    # Per-call max depth should override model-level setting
+    three_level_recursive_model.max_serialization_depth = 2
+    data = three_level_recursive_model.to_dict(max_serialization_depth=0)
+
+    # At depth 0, no relationships should be serialized
+    assert "children" not in data
+    assert "name" in data
+
+
+def test_depth_limit_enforcement_nested_model(get_instance):
+    """Test depth limit enforcement with NestedModel"""
+    nested = get_instance(NestedModel, model_id=get_instance(FlatModel).id)
+
+    # At depth 0, nested relationships should not be serialized
+    data = nested.to_dict(max_serialization_depth=0)
+    assert "model" not in data
+
+    # At depth 1, one level of nesting should work
+    data = nested.to_dict(max_serialization_depth=1)
+    assert "model" in data
+    nested_model = data["model"]
+    assert "id" in nested_model
+    assert "string" in nested_model
+    # FlatModel doesn't have a relationship back, so no further nesting
+
+
+def test_depth_limit_with_rules(three_level_recursive_model):
+    """Test that depth limit works together with existing rules"""
+    # Combine depth limit with rules
+    data = three_level_recursive_model.to_dict(
+        max_serialization_depth=1, rules=("-children.id",)
+    )
+
+    assert "children" in data
+    assert "id" not in data["children"][0]  # Rule applied
+    assert "name" in data["children"][0]
+    # Depth limit still enforced
+    assert "children" not in data["children"][0]
+
+
+def test_depth_limit_zero(get_instance):
+    """Test that depth 0 prevents all relationship serialization"""
+    root = get_instance(RecursiveModel)
+    get_instance(RecursiveModel, parent_id=root.id)
+
+    data = root.to_dict(max_serialization_depth=0)
+
+    # Only top-level fields should be present
+    assert "id" in data
+    assert "name" in data
+    assert "children" not in data
+
+
+@pytest.mark.parametrize("depth", [1, 2])
+def test_depth_limit_multiple_levels(three_level_recursive_model, depth):
+    data = three_level_recursive_model.to_dict(max_serialization_depth=depth)
+
+    for i in range(depth):
+        assert "id" in data
+        assert "name" in data
+        if i < depth:
+            assert "children" in data
+            data = data["children"][0]
+
+
+def test_depth_limit_infinity(three_level_recursive_model):
+    """Test that math.inf allows unlimited depth"""
+    data = three_level_recursive_model.to_dict(max_serialization_depth=math.inf)
+
+    # Should serialize all levels
+    assert "children" in data
+    assert "children" in data["children"][0]
+    assert "children" in data["children"][0]["children"][0]
+
+
+def test_model_level_depth_override(get_instance):
+    """Test that per-call parameter overrides model-level setting"""
+    root = get_instance(RecursiveModel)
+    get_instance(RecursiveModel, parent_id=root.id)
+
+    # Set model-level depth to 1
+    root.max_serialization_depth = 1
+    # But override with per-call parameter
+    data = root.to_dict(max_serialization_depth=0)
+
+    # Per-call parameter should win
+    assert "children" not in data
+
+
+def test_to_dict_param_overrides_class_level_max_depth(three_level_recursive_model):
+    """Test that max_serialization_depth parameter in to_dict()
+    overrides class-level setting"""
+    three_level_recursive_model.max_serialization_depth = 1
+
+    # First, verify class-level setting works when no parameter is passed
+    data_without_param = three_level_recursive_model.to_dict()
+    assert "children" in data_without_param
+    assert "children" not in data_without_param["children"][0]  # Child has children field
+
+    # Now verify that passing parameter overrides class-level setting
+    # Override with depth 2 (should allow grandchildren)
+    data_with_override = three_level_recursive_model.to_dict(max_serialization_depth=2)
+    assert "children" in data_with_override
+    # Parameter override allows deeper nesting
+    assert "children" in data_with_override["children"][0]
+
+    # Override with depth 0 (should prevent all relationships)
+    data_with_zero = three_level_recursive_model.to_dict(max_serialization_depth=0)
+    assert "children" not in data_with_zero
+    assert "id" in data_with_zero
+    assert "name" in data_with_zero
+
+    # Override with math.inf (should allow unlimited depth)
+    data_with_inf = three_level_recursive_model.to_dict(max_serialization_depth=math.inf)
+    assert "children" in data_with_inf
+    assert "children" in data_with_inf["children"][0]
+    assert "children" in data_with_inf["children"][0]["children"][0]