TinyDB insertion fails

Question

I try to insert the JSON serialization of a Python object into tinydb. It works one time and fails after that.

from tinydb import TinyDB, Query
import json

class Test:
    def __init__(self):
        self.test = "a"

    def to_JSON(self):
        return json.dumps(self, default=lambda o: o.__dict__)

db = TinyDB("test.json")
print(Test().to_JSON)
db.insert(Test().to_JSON())
print("Second insert")
db.insert(Test().to_JSON())

Leads to

{"test": "a"}
Second insert
Traceback (most recent call last):
  File "test.py", line 15, in <module>
    db.insert(Test().to_JSON())
  File "/usr/lib/python3.4/site-packages/tinydb/database.py", line 287, in insert
    data = self._read()
  File "/usr/lib/python3.4/site-packages/tinydb/database.py", line 248, in _read
    return self._storage.read()
  File "/usr/lib/python3.4/site-packages/tinydb/database.py", line 38, in read
    data[eid] = Element(val, eid)
  File "/usr/lib/python3.4/site-packages/tinydb/database.py", line 20, in __init__
    self.update(value)
ValueError: dictionary update sequence element #0 has length 1; 2 is required

The JSON itself looks pretty valid to me, so why does tinydb fail to insert it a second time?

Answer 1

I was holding it wrong. insert() expects a dict object while json.dumps() generates a string.

from tinydb import TinyDB, Query
import json

class Test:
    def __init__(self):
        self.test = "a"

    def to_JSON(self):
        return json.loads(json.dumps(self, default=lambda o: o.__dict__))

db = TinyDB("test.json")
db.insert(Test().to_JSON())
print("Second insert")
db.insert(Test().to_JSON())