Assigner Assignments Must Satisfy JSON Schema Type Constraints

When an Assigner populates Fields, the values it assigns must match the JSON Schema type defined for the corresponding data field in model.py, and they must be representable in JSON (e.g., as strings, numbers, booleans, etc.).

A clear example is Python’s timedelta class.

protocol.aimd:

Seconds：{{var|seconds}}
Represent the above value in `duration` format: {{var|duration}}

model.py:

from datetime import timedelta
from pydantic import BaseModel

class TimeModel(BaseModel):
    seconds: int
    duration: timedelta

If we want an Assigner to convert seconds into duration, we must ensure that the value assigned to duration follows the JSON Schema format.

Because timedelta is represented in JSON Schema as a duration string (e.g., P1DT2H30M for 1 day 2 hours 30 minutes, PT1H30M for 1 hour 30 minutes), we first convert the timedelta to an ISO 8601 string.

assigner.py (safe implementation):

from datetime import timedelta
from airalogy.assigner import AssignerResult, assigner
from airalogy.iso import timedelta_to_iso

@assigner(
    assigned_fields=["duration"],
    dependent_fields=["seconds"],
    mode="auto",
)
def convert_seconds_to_duration(dependent_fields: dict) -> AssignerResult:
    seconds = dependent_fields["seconds"]
    duration = timedelta(seconds=seconds)
    return AssignerResult(
        assigned_fields={
            "duration": timedelta_to_iso(duration),
        },
    )

Incorrect (unsafe) implementation that may fail JSON Schema validation:

@assigner(
    assigned_fields=["duration"],
    dependent_fields=["seconds"],
    mode="auto",
)
def convert_seconds_to_duration(dependent_fields: dict) -> AssignerResult:
    seconds = dependent_fields["seconds"]
    duration = timedelta(seconds=seconds)
    return AssignerResult(
        assigned_fields={
            "duration": duration,  # Unsafe: direct timedelta assignment will likely violate JSON Schema
        },
    )

airalogy.iso Module

The airalogy.iso module provides handy helpers for converting common Python complex types to ISO strings.

timedelta_to_iso

Convert a timedelta object to an ISO 8601 string.

from datetime import timedelta
from airalogy.iso import timedelta_to_iso

timedelta_obj = timedelta(days=1, hours=2, minutes=30)
iso_string = timedelta_to_iso(timedelta_obj)
print(iso_string)  # Output: P1DT2H30M