hyperdb.del() should not add null value for already deleted or non-existent keys

[e-e-e]

Currently deleting keys adds a null value to the db regardless of if the key exists or not. It would be great to check if the key exists or not before deleting to avoid unnecessary data in the db.

I wrote some tests for this the first and last are currently failing.

tape('does not delete non existent keys', function (t) {
  var db = create.one()
  db.del('hello', function (err, node) {
    t.error(err, 'no error')
    t.same(db._writers[0].length(), 0)
    t.end()
  })
})

tape('does not delete non existent keys', function (t) {
  var db = create.one()
  db.put('hello', 'world', function (err, node) {
    t.error(err, 'no error')
    db.del('hello', function (err, node) {
      t.error(err, 'no error')
      t.same(db._writers[0].length(), 2)
      t.end()
    })
  })
})


tape('does not delete non existent keys', function (t) {
  var db = create.one()
  db.put('hello', 'world', function (err, node) {
    t.error(err, 'no error')
    db.del('hello', function (err, node) {
      t.error(err, 'no error')
      t.same(db._writers[0].length(), 2)
      db.del('hello', function (err, node) {
        t.error(err, 'no error')
        t.same(db._writers[0].length(), 2)
        t.end()
      })
    })
  })
})

[mafintosh]

I think we can efficiently to this while walking the trie and see if we end up visiting the same key if someone wants to attempt a pr

[mafintosh]

@e-e-e i think extending this with an option that makes it not overwrite a put with the same value seems relevant as well

[e-e-e]

@mafintosh just playing around with writing a staging area for hyperdb's and realised that recording a del for a non-existent key is a really key feature. It helps to easily see if the staged db has deleted a key without having to add that key.

I think doing just as you suggest, not overwriting puts is a better idea than not adding the del for non-existent items.