How to Check for Session Changes

• The advanced session has_changes property indicates whether any entities were added, modified, or deleted within the session.

• Note: The has_changes property is cleared (reset to False) after calling save_changes.

with store.open_session() as session:
    # No changes made yet - 'has_changes' will be False
    self.assertFalse(session.has_changes())

    # Store a new entity within the session
    session.store(Employee(first_name="John", last_name="Doe"))

    # 'has_changes' will now be True
    self.assertTrue(session.has_changes())

    # 'has_changes' will reset to False after saving changes
    session.save_changes()
    self.assertFalse(session.has_changes())

• Use the session's advanced method what_changed to get all changes made to all the entities tracked by the session.

• For each entity that was modified, the details will include:

  • The name and path of the changed field
  • Its old and new values
  • The type of change

• Note: what_changed reports changes made prior to calling save_changes.
  Calling it immediately after save_changes will return no results, as the changes are cleared.

Example I

with store.open_session() as session:
    # Store (add) new entities, they will be tracked by the session
    session.store(Employee(first_name="John", last_name="Doe"), "employees/1-A")
    session.store(Employee(first_name="Jane", last_name="Doe"), "employees/2-A")

    # Call 'what_changed' to get all changes in the session
    changes = session.advanced.what_changed()
    self.assertEquals(2, len(changes))  # 2 entites were added

    # Get the change details for an entity, specify the entity ID
    changes_for_employee = changes["employees/1-A"]
    self.assertEquals(1, len(changes_for_employee))  # a single change for this entity (adding)

    # Get the change type
    change_type = changes_for_employee[0].change
    self.assertEquals(DocumentsChanges.ChangeType.DOCUMENT_ADDED, change_type)

    session.save_changes()

Example II

with store.open_session() as session:
    # Load the entities, they will be tracked by the session
    employee_1 = session.load("employees/1-A", Employee)
    employee_2 = session.load("employees/2-A", Employee)

    # Modify entities
    employee_1.first_name = "Jim"
    employee_1.last_name = "Brown"
    employee_2.last_name = "Smith"

    # Delete an entity
    session.delete(employee_2)

    # Call 'what_changed' to get all changes in the session
    changes = session.advanced.what_changed()

    # Get the change details for an entity, specify the entity ID
    changes_for_employee = changes["employees/1-A"]

    self.assertEquals("FirstName", changes_for_employee[0].field_name)  # Field name
    self.assertEquals("Jim", changes_for_employee[0].field_new_value)  # New value
    self.assertEquals(
        DocumentsChanges.ChangeType.FIELD_CHANGED, changes_for_employee[0].change
    )  # Change type

    self.assertEquals("LastName", changes_for_employee[1].field_name)  # Field name
    self.assertEquals("Brown", changes_for_employee[1].field_new_value)  # New value
    self.assertEquals(
        DocumentsChanges.ChangeType.FIELD_CHANGED, changes_for_employee[1].change
    )  # Change type

    # Note: for employee2 - even though the LastName was changed to 'Smith',
    # the only reported change is the latest modification, which is the delete action.
    changes_for_employee = changes["employees/2-A"]
    self.assertEquals(DocumentsChanges.ChangeType.DOCUMENT_DELETED, changes_for_employee[0].change)

    session.save_changes()

# has_changes
def has_changes(self) -> bool: ...

# what_changed
def what_changed(self) -> Dict[str, List[DocumentsChanges]]: ...

class DocumentsChanges:

    def __init__(
        self,
        field_old_value: object,
        field_new_value: object,
        change: DocumentsChanges.ChangeType,
        field_name: str = None,
        field_path: str = None,
    ): ...

    class ChangeType(Enum):
        DOCUMENT_DELETED = "DocumentDeleted"
        DOCUMENT_ADDED = "DocumentAdded"
        FIELD_CHANGED = "FieldChanged"
        NEW_FIELD = "NewField"
        REMOVED_FIELD = "RemovedField"
        ARRAY_VALUE_CHANGED = "ArrayValueChanged"
        ARRAY_VALUE_ADDED = "ArrayValueAdded"
        ARRAY_VALUE_REMOVED = "ArrayValueRemoved"