How to recreate a HexaryTrie from a saved database

Question

I am trying to create a HexaryTrie from the database that the trie writes to.

Here is my Code:

from trie import (
    HexaryTrie,
)

db = {}
trie1 = HexaryTrie(db)

trie1[b'deadbeef'] = b'deadbeef'
...

trie2 = HexaryTrie(db)

print(trie1.root_hash)
print(trie2.root_hash)
# ^ these print different root hashes :(

I saw in py-trie, that the HexaryTrie constructor is:

def __init__(self, db, root_hash=BLANK_NODE_HASH, prune=False):
    self.db = db
    validate_is_bytes(root_hash)
    self.root_hash = root_hash
    self.is_pruning = prune

Is there a way to use the db that is being created to "re"-create the trie?

Thank you in advance :)

Answer 1

Is there a way to use the db that is being created to "re"-create the trie?

Yes, with one missing piece.

A HexaryTrie instance keeps track of its current root hash as it updates. But if you load a fresh trie from the database, you have to tell it which root hash to bootstrap from.

So, set up your initial data:

db = {}
trie1 = HexaryTrie(db)

trie1[b'deadbeef'] = b'deadbeef'
...

Recreate the original problem:

trie2 = HexaryTrie(db)
# because this doesn't have a root hash to look up the nodes, this
# returns empty data. Side note: I wish it raised a KeyError here...
assert trie2[b'deadbeef'] == b''

To look up the data successfully, you can change the root hash at runtime:

trie2.root_hash = trie1.root_hash
# The trie can now find the desired data:
assert trie2[b'deadbeef'] == b'deadbeef'

Alternatively, create the trie with the correct root hash:

trie3 = HexaryTrie(db, root_hash=trie1.root_hash)
assert trie3[b'deadbeef'] == b'deadbeef'