JSON Compatible Encoder¶

There are some cases where you might need to convert a data type (like a Pydantic model) to something compatible with JSON (like a dict, list, etc).

For example, if you need to store it in a database.

For that, FastAPI provides a jsonable_encoder() function.

Using the jsonable_encoder¶

Let's imagine that you have a database fake_db that only receives JSON compatible data.

For example, it doesn't receive datetime objects, as those are not compatible with JSON.

So, a datetime object would have to be converted to a str containing the data in ISO format.

The same way, this database wouldn't receive a Pydantic model (an object with attributes), only a dict.

You can use jsonable_encoder for that.

It receives an object, like a Pydantic model, and returns a JSON compatible version:

fromdatetimeimport datetime
fromfastapiimport FastAPI
fromfastapi.encodersimport jsonable_encoder
frompydanticimport BaseModel
fake_db = {}
classItem(BaseModel):
 title: str
 timestamp: datetime
 description: str | None = None
app = FastAPI()
@app.put("/items/{id}")
defupdate_item(id: str, item: Item):
 json_compatible_item_data = jsonable_encoder(item)
 fake_db[id] = json_compatible_item_data

In this example, it would convert the Pydantic model to a dict, and the datetime to a str.

The result of calling it is something that can be encoded with the Python standard json.dumps().

It doesn't return a large str containing the data in JSON format (as a string). It returns a Python standard data structure (e.g. a dict) with values and sub-values that are all compatible with JSON.