When building RESTful APIs that connect to a MongoDB databases, the error below might come up when you attempt to serialize a mongodb record _id:
TypeError: ObjectId('51948e86c25f4b1d1e86c25f') is not JSON serializable
The error is caused by an incompatibility between JSON and the BSON ObjectId data type. One way around this error is to create a custom JSON Encoder that can handle ObjectId data.
[sourcecode lang=”python”]
import json
from bson import ObjectId
class JSONEncoder(json.JSONEncoder):
def default(self, item):
if isinstance(item, ObjectId):
return str(item)
return json.JSONEncoder.default(self, item)
[/sourcecode]
After creating this encoder, you can then create a custom JSONField that takes advantage of it in your serializers.py file:
[sourcecode lang=”python”]
class JSONFIeld(serializers.Field):
def to_representation(self, value):
try:
result = json.dumps(
value, skipkeys=True,
allow_nan=True,cls=JSONEncoder
)
return result
except ValueError:
return ”
[/sourcecode]
If you’ll be writing to the database, you’ll also want to implement a .to_internal_value() method to handle conversion into data types that are safe for the database. After doing this, you can use this custom JSONField as a serializer field.