Applies prefix twice on nested sublevel

[vweevers]

Because the prefix is applied on open:

subleveldown/leveldown.js

Lines 90 to 93 in 42eca35

	if (subdb && subdb.prefix) {
	self.prefix = subdb.prefix + self.prefix
	self.leveldown = reachdown(subdb.db, matchdown, false)
	} else {

So if you open, close and reopen, self.prefix = subdb.prefix + self.prefix happens twice.

There are more issues with the open logic (#60, #77), so let's refactor it a bit.

[MeirionHughes]

yeah I've got this too. 4.1.0 was fine, but on 4.1.1 I get prefix duplication.

I'm trying to replicate it, but its proving troublesome as if I straight up make the subs it works. In practice my code is creating subs "on the fly" then caching a helper class that manages the subdb.

[MeirionHughes]

I've managed to duplicate it:

  let db = levelup(encoding(memdown()));

  let fooDb = sub(db, "foo");
  let barDb = sub(fooDb, "bar");
  let rayDb = sub(barDb, "ray"); 

  await fooDb.put("def", "one")
  await barDb.put("def", "two")

  await rayDb.put("123", "hello world");
  await rayDb.put("124", "hello world");
  await rayDb.put("125", "hello world");

result with with subleveldown@4.1.1:

 !foo!!bar!def
 !foo!!foo!!bar!!ray!123
 !foo!!foo!!bar!!ray!124
 !foo!!foo!!bar!!ray!125
 !foo!def

while with subleveldown@4.1.0:

 !foo!!bar!!ray!123
 !foo!!bar!!ray!124
 !foo!!bar!!ray!125
 !foo!!bar!def
 !foo!def

[vweevers]

@MeirionHughes We've already got a test for it. And 4.0.0 and 4.1.0 were broken (in other ways), so while it may seem 4.1.1 has the issue, it actually revealed it, and it has been here since 3.0.0.

[vweevers]

Although... wait. The issue you're describing is a separate one (not about re- opening) that we might be able to fix on a shorter term. It's probably a race issue between the different sublevels all wanting to open the db.

Simple workaround is to do:

let db = levelup(encoding(memdown()))

db.on('open', function () {
  // create your sublevels now
})

[MeirionHughes]

I've already tried with:

  let db = levelup(encoding(memdown()));

  await db.open();

  let fooDb = sub(db, "foo");
  await fooDb.open();
  
  let barDb = sub(fooDb, "bar");
  await barDb.open();

  let rayDb = sub(barDb, "ray"); 
  await rayDb.open();

and I get the same.

I was going to see what difference this really has on this 3-layer nesting.

[vweevers]

I was going to see what difference this really has on this 3-layer nesting.

That's been replaced in a later version

[vweevers]

OK, I'm able to reproduce your issue on master as well.

[vweevers]

Possible fix is to replace this (which can land on subdown rather than leveldown, so we end up wrapping subdown with subdown, hence the double prefix):

subleveldown/leveldown.js

Line 92 in 279ac43

self.leveldown = reachdown(subdb.db, matchdown, false)

With:

self.leveldown = subdb.leveldown

@MeirionHughes Could you try that out?

[MeirionHughes]

yeah that seems to do the trick

[vweevers]

We could release that fix as semver-patch, but consumers can in theory lose access to already stored data (with a double prefix)... does that make it a breaking change? Yolo.

[vweevers]

4.1.4

[MeirionHughes]

cheers: looks like its working well and I have about five sub-levels too. Thanks for the quick fix.