fix(jira): serialize datetime in changelog for JSON compatibility (#768)

Add field_serializer to JiraChangelog model to ensure datetime fields
are properly serialized to ISO 8601 format for JSON. This fixes the
"Object of type datetime is not JSON serializable" error when using
expand='changelog' with Jira search.

- Add @field_serializer("created") to JiraChangelog
- Update to_simplified_dict() to use isoformat()
- Add regression tests for datetime serialization
- Update existing test expectations for ISO 8601 format

Fixes #749
Github-Issue:#749

Author: sooperset

src/mcp_atlassian/models/jira/common.py

@@ -9,7 +9,7 @@
 from datetime import datetime
 from typing import Any
 
-from pydantic import Field
+from pydantic import Field, field_serializer
 
 from mcp_atlassian.utils import parse_date
 
@@ -518,6 +518,13 @@ class JiraChangelog(ApiModel, TimestampMixin):
     created: datetime | None = None
     items: list[JiraChangelogItem] = Field(default_factory=list)
 
+    @field_serializer("created")
+    def serialize_created(self, value: datetime | None) -> str | None:
+        """Serialize datetime to ISO 8601 string for JSON compatibility."""
+        if value is None:
+            return None
+        return value.isoformat()
+
     @classmethod
     def from_api_response(cls, data: dict[str, Any], **kwargs: Any) -> "JiraChangelog":
         """
@@ -578,6 +585,6 @@ def to_simplified_dict(self) -> dict[str, Any]:
             result["author"] = self.author.to_simplified_dict()
 
         if self.created:
-            result["created"] = str(self.created)
+            result["created"] = self.created.isoformat()
 
         return result

tests/unit/jira/test_issues.py

@@ -1357,7 +1357,7 @@ def test_batch_get_changelogs_cloud(self, issues_mixin: IssuesMixin):
                             "email": None,
                             "name": "Test User 1",
                         },
-                        "created": "2024-01-05 10:06:03.548000+08:00",
+                        "created": "2024-01-05T10:06:03.548000+08:00",
                         "items": [
                             {
                                 "field": "IssueParentAssociation",
@@ -1382,7 +1382,7 @@ def test_batch_get_changelogs_cloud(self, issues_mixin: IssuesMixin):
                             "email": None,
                             "name": "Test User 2",
                         },
-                        "created": "2024-01-01 11:00:00+00:00",
+                        "created": "2024-01-01T11:00:00+00:00",
                         "items": [
                             {
                                 "field": "Parent",
@@ -1399,7 +1399,7 @@ def test_batch_get_changelogs_cloud(self, issues_mixin: IssuesMixin):
                             "email": None,
                             "name": "Test User 3",
                         },
-                        "created": "2024-01-06 10:06:03.548000+08:00",
+                        "created": "2024-01-06T10:06:03.548000+08:00",
                         "items": [
                             {
                                 "field": "Parent",
@@ -1418,7 +1418,7 @@ def test_batch_get_changelogs_cloud(self, issues_mixin: IssuesMixin):
                             "email": None,
                             "name": "Test User 1",
                         },
-                        "created": "2024-01-10 10:06:03.548000+08:00",
+                        "created": "2024-01-10T10:06:03.548000+08:00",
                         "items": [
                             {
                                 "field": "Parent",

tests/unit/models/test_jira_models.py

@@ -5,8 +5,10 @@
 and the simplified dictionary conversion for API responses.
 """
 
+import json
 import os
 import re
+from datetime import datetime, timezone
 
 import pytest
 
@@ -35,6 +37,7 @@
     JiraUser,
     JiraWorklog,
 )
+from src.mcp_atlassian.models.jira.common import JiraChangelog
 
 # Optional: Import real API client for optional real-data testing
 try:
@@ -1945,3 +1948,45 @@ def test_real_jira_worklog(self, use_real_jira_data, default_jira_issue_key):
 
         except Exception as e:
             pytest.fail(f"Error testing real Jira worklog: {e}")
+
+
+class TestJiraChangelog:
+    """Tests for JiraChangelog datetime serialization (fixes #749)."""
+
+    def test_created_datetime_serialization(self):
+        """Test that datetime created field serializes to JSON properly."""
+        changelog = JiraChangelog(
+            id="12345",
+            created=datetime(2024, 1, 15, 10, 30, 0, tzinfo=timezone.utc),
+            items=[],
+        )
+
+        # model_dump should serialize datetime to ISO string
+        dumped = changelog.model_dump(mode="json")
+        assert isinstance(dumped["created"], str)
+        assert "2024-01-15" in dumped["created"]
+
+        # to_simplified_dict should also work
+        simplified = changelog.to_simplified_dict()
+        assert isinstance(simplified["created"], str)
+
+        # Final json.dumps should not raise
+        json_str = json.dumps(simplified)
+        assert "2024-01-15" in json_str
+
+    def test_from_api_response_with_changelog(self):
+        """Test JiraChangelog.from_api_response handles dates correctly."""
+        data = {
+            "id": "100",
+            "created": "2024-01-15T10:30:00.000+0000",
+            "author": {"displayName": "Test User"},
+            "items": [{"field": "status", "fromString": "Open", "toString": "Done"}],
+        }
+
+        changelog = JiraChangelog.from_api_response(data)
+        assert isinstance(changelog.created, datetime)
+
+        # Should serialize cleanly to JSON
+        simplified = changelog.to_simplified_dict()
+        json_str = json.dumps(simplified)
+        assert "2024-01-15" in json_str