Add Custom Base Model point description

README.md

@@ -368,8 +368,57 @@ In short, GIL allows only one thread to work at a time, which makes it useless f
 2. https://stackoverflow.com/questions/65342833/fastapi-uploadfile-is-slow-compared-to-flask
 3. https://stackoverflow.com/questions/71516140/fastapi-runs-api-calls-in-serial-instead-of-parallel-fashion
 
-### 9. Custom base model model from day 0, 
-convert datetime to common standard
+### 9. Custom base model from day 0.
+Having a controllable global pydantic base model allows us to customize all the models within the app.
+For example, we could have a standard datetime format or add a super method for all subclasses of the base model.
+```python
+from datetime import datetime
+from zoneinfo import ZoneInfo
+
+import orjson
+from fastapi.encoders import jsonable_encoder
+from pydantic import BaseModel, root_validator
+
+
+def orjson_dumps(v, *, default):
+    # orjson.dumps returns bytes, to match standard json.dumps we need to decode
+    return orjson.dumps(v, default=default).decode()
+
+
+def convert_datetime_to_gmt(dt: datetime) -> str:
+    if not dt.tzinfo:
+        dt = dt.replace(tzinfo=ZoneInfo("UTC"))
+
+    return dt.strftime("%Y-%m-%dT%H:%M:%S%z")
+
+
+class ORJSONModel(BaseModel):
+    class Config:
+        json_loads = orjson.loads
+        json_dumps = orjson_dumps
+        json_encoders = {datetime: convert_datetime_to_gmt}  # method for customer JSON encoding of datetime fields
+
+    @root_validator()
+    def set_null_microseconds(cls, data: dict) -> dict:
+       """Drops microseconds in all the datetime field values."""
+        datetime_fields = {
+            k: v.replace(microsecond=0)
+            for k, v in data.items()
+            if isinstance(k, datetime)
+        }
+
+        return {**data, **datetime_fields}
+
+    def serializable_dict(self, **kwargs):
+       """Return a dict which contains only serializable fields."""
+        default_dict = super().dict(**kwargs)
+
+        return jsonable_encoder(default_dict)
+```
+In the example above we have decided to make a global base model which: 
+- uses [orjson](https://github.com/ijl/orjson) to serialize data
+- drops microseconds to 0 in all date formats
+- serializes all datetime fields to standard format with explicit timezone 
 ### 10. Docs
 1. Unless your API is public, hide docs by default. Show it explicitly on the selected envs only.
 ```python