Empty table does not persist

[dmarsic]

Hi,

I attempted to create empty tables, similar to CREATE TABLE in SQL. TinyDB currently does not persist empty tables:

1. My initial approach didn't create a table because Table does not call _update_table() when creating an instance.

In [1]: from tinydb import TinyDB

In [2]: db = TinyDB("example.json")

In [3]: t = db.table("emptytbl")

In [4]: db.close()

In [5]: from pathlib import Path

In [6]: Path("example.json").read_text()
Out[6]: ''

2. Workaround with adding truncate() call to ensure that the table gets written.

In [1]: from tinydb import TinyDB

In [2]: db = TinyDB("example.json")

In [3]: t = db.table("emptytbl")

In [4]: t.truncate()

In [5]: db.close()

In [6]: from pathlib import Path

In [7]: Path("example.json").read_text()
Out[7]: '{"emptytbl": {}}'

I'm new to the project so I'm not sure if this is intentional. I propose adding a flag to Table, persist_empty: bool = False, and if the flag is true then call _update_table to ensure an empty table gets immediately written.

I'm happy to submit a PR if that makes sense.

[msiemens]

That's an interesting point. You're right, right now calling table(...) is a lazy operation that does not touch the file system until data is written to the table for the first time. I'd be happy to accept a PR for this 🙂