feat: Computed/virtual child-tables

- They need to be a non-data descriptor i.e. cached_property or
  equivalent
- When "loading from DB", we will trigger the descriptor
- The descriptor can return dict or docs for better DX.
- We initialize docs as normal child tables

frappe/core/doctype/doctype/doctype.py

@@ -1641,10 +1641,9 @@ def validate_fields(meta: Meta):
 				title=_("Invalid Option"),
 			)
 
-		if meta.is_virtual != child_doctype_meta.is_virtual:
-			error_msg = " should be virtual." if meta.is_virtual else " cannot be virtual."
+		if meta.is_virtual and not child_doctype_meta.is_virtual:
 			frappe.throw(
-				_("Child Table {0} for field {1}" + error_msg).format(
+				_("Cannot put a non-virtual Child Table {0} for field {1} on Virtual parent").format(
 					frappe.bold(doctype), frappe.bold(docfield.fieldname)
 				),
 				title=_("Invalid Option"),

frappe/core/doctype/user/user.json

@@ -111,7 +111,9 @@
   "column_break_65",
   "api_secret",
   "onboarding_status",
-  "connections_tab"
+  "connections_tab",
+  "sessions_tab",
+  "active_sessions"
  ],
  "fields": [
   {
@@ -834,6 +836,17 @@
    "fieldname": "show_absolute_datetime_in_timeline",
    "fieldtype": "Check",
    "label": "Show Absolute Datetime in Timeline"
+  },
+  {
+   "fieldname": "sessions_tab",
+   "fieldtype": "Tab Break",
+   "label": "Sessions"
+  },
+  {
+   "fieldname": "active_sessions",
+   "fieldtype": "Table",
+   "label": "Active Sessions",
+   "options": "User Session Display"
   }
  ],
  "icon": "fa fa-user",
@@ -892,7 +905,7 @@
   }
  ],
  "make_attachments_public": 1,
- "modified": "2025-06-05 23:55:27.884061",
+ "modified": "2025-06-23 14:24:20.505385",
  "modified_by": "Administrator",
  "module": "Core",
  "name": "User",

frappe/core/doctype/user/user.py

@@ -3,6 +3,7 @@
 
 from collections.abc import Iterable
 from datetime import timedelta
+from functools import cached_property
 
 import frappe
 import frappe.defaults
@@ -62,9 +63,11 @@ class User(Document):
 		from frappe.core.doctype.has_role.has_role import HasRole
 		from frappe.core.doctype.user_email.user_email import UserEmail
 		from frappe.core.doctype.user_role_profile.user_role_profile import UserRoleProfile
+		from frappe.core.doctype.user_session_display.user_session_display import UserSessionDisplay
 		from frappe.core.doctype.user_social_login.user_social_login import UserSocialLogin
 		from frappe.types import DF
 
+		active_sessions: DF.Table[UserSessionDisplay]
 		allowed_in_mentions: DF.Check
 		api_key: DF.Data | None
 		api_secret: DF.Password | None
@@ -142,6 +145,35 @@ class User(Document):
 
 	__new_password = None
 
+	@cached_property
+	def active_sessions(self):
+		sessions = frappe.qb.DocType("Sessions")
+
+		sessions_data = (
+			frappe.qb.from_(sessions)
+			.select(sessions.user, sessions.sessiondata, sessions.sid)
+			.where(sessions.user == self.name)
+		).run(as_dict=True)
+
+		def mask(sid: str):
+			return sid[:4] + "*" * (len(sid) - 4)
+
+		session_docs = []
+		for session in sessions_data:
+			data = frappe.parse_json(session.sessiondata)
+			session_docs.append(
+				{
+					"name": mask(session.sid),
+					"id": mask(session.sid),
+					"owner": session.user,
+					"modified_by": session.user,
+					"ip_address": data.session_ip,
+					"last_updated": data.last_updated,
+					"session_created": data.creation,
+				}
+			)
+		return session_docs
+
 	def __setup__(self):
 		# because it is handled separately
 		self.flags.ignore_save_passwords = ["new_password"]

frappe/core/doctype/user_session_display/user_session_display.json

@@ -0,0 +1,54 @@
+{
+ "actions": [],
+ "allow_rename": 1,
+ "creation": "2025-06-23 14:19:48.353900",
+ "doctype": "DocType",
+ "engine": "InnoDB",
+ "field_order": [
+  "id",
+  "ip_address",
+  "session_created",
+  "last_updated"
+ ],
+ "fields": [
+  {
+   "fieldname": "id",
+   "fieldtype": "Data",
+   "in_list_view": 1,
+   "label": "ID"
+  },
+  {
+   "fieldname": "ip_address",
+   "fieldtype": "Data",
+   "in_list_view": 1,
+   "label": "IP Address"
+  },
+  {
+   "fieldname": "session_created",
+   "fieldtype": "Datetime",
+   "in_list_view": 1,
+   "label": "Session Created"
+  },
+  {
+   "fieldname": "last_updated",
+   "fieldtype": "Datetime",
+   "in_list_view": 1,
+   "label": "Last Updated"
+  }
+ ],
+ "grid_page_length": 50,
+ "index_web_pages_for_search": 1,
+ "is_virtual": 1,
+ "istable": 1,
+ "links": [],
+ "modified": "2025-06-23 14:25:15.690896",
+ "modified_by": "Administrator",
+ "module": "Core",
+ "name": "User Session Display",
+ "owner": "Administrator",
+ "permissions": [],
+ "row_format": "Dynamic",
+ "sort_field": "creation",
+ "sort_order": "DESC",
+ "states": []
+}

frappe/core/doctype/user_session_display/user_session_display.py

@@ -0,0 +1,48 @@
+# Copyright (c) 2025, Frappe Technologies and contributors
+# For license information, please see license.txt
+
+# import frappe
+from frappe.model.document import Document
+
+
+class UserSessionDisplay(Document):
+	# begin: auto-generated types
+	# This code is auto-generated. Do not modify anything in this block.
+
+	from typing import TYPE_CHECKING
+
+	if TYPE_CHECKING:
+		from frappe.types import DF
+
+		id: DF.Data | None
+		ip_address: DF.Data | None
+		last_updated: DF.Datetime | None
+		parent: DF.Data
+		parentfield: DF.Data
+		parenttype: DF.Data
+		session_created: DF.Datetime | None
+	# end: auto-generated types
+
+	def db_insert(self, *args, **kwargs):
+		raise NotImplementedError
+
+	def load_from_db(self):
+		raise NotImplementedError
+
+	def db_update(self):
+		raise NotImplementedError
+
+	def delete(self):
+		raise NotImplementedError
+
+	@staticmethod
+	def get_list(filters=None, page_length=20, **kwargs):
+		pass
+
+	@staticmethod
+	def get_count(filters=None, **kwargs):
+		pass
+
+	@staticmethod
+	def get_stats(**kwargs):
+		pass

frappe/model/document.py

@@ -274,7 +274,13 @@ class Document(BaseDocument):
 		for fieldname, child_doctype in self._table_fieldnames.items():
 			# Make sure not to query the DB for a child table, if it is a virtual one.
 			if not is_doctype and is_virtual_doctype(child_doctype):
-				self.set(fieldname, [])
+				# Users must specify non-data descriptor/cached_property for computed table
+				# Remove previous value if any, required for reload.
+				self.__dict__.pop(fieldname, None)
+				values = getattr(self, fieldname, [])
+				# Convert to documents
+				self.__dict__[fieldname] = []
+				self.extend(fieldname, values)
 				continue
 
 			if is_doctype: