How to total smartpy.TMutez type stored as values in smartpy.bigmap?

Question

I have the following smartpy.bigmap in smart contract storage:

import smartpy as sp
self.data.init(bgmp=sp.bigmap(tkey=sp.TAddress,tvalue=sp.TMutez))

I would like to total all the stored tvalue so based on the SmartPy docs I tried:

total=sp.tez(0)
sp.for v in self.data.bgmp.values():
    total+=v

I then wish to sp.verify(total>=minAmount<sp.TMutez>)

When run in the latest SmartPy.io IDE the following error is produced:

Error:
Failure: Missing var v in env []

If I hardcode total+=sp.tez(1) the error becomes:

Error:
WrongCondition in line 18: (sp.tez(0) + sp.tez(1)) >= self.data.minAmount

I am doubtful that this is a correctly totaled sp.TMutez value.

Any help is much appreciated!

Answer 1

There is no way of iterating over all values in a big_map in the language to which SmartPy compiles (Michelson). So it doesn't surprise me that this doesn't work in SmartPy either. Indeed, according the SmartPy documentation:

e.values(): Returns the list of values of a map, sorted by keys.

Here, I presume that map refers exclusively to normal, "simple" maps and not big_maps.

However, there is probably some other way of solving your problem. For instance, you can keep track of the big_map's total in a separate variable, and update it each time the big_map is updated.

Answer 2

@arvidj is right of course and you cannot iterate on a bigmap. You need to keep your sum in the storage.

You also have another error: if it was a map, you would still need to use a local variable to accumulate the sum. This is introduced by total = sp.newLocal('total', ...). What the error is telling you is that your v is escaping it`s scope. With 1, we could also analyze the mistake but don't currently. The only way to currently see it is to check the generated script (in the output panel) which shows a code that you don't expect.

Then, with local variables. To set a local variable (introduced by newLocal) you currently need to use total.set(...). It will be changed to total.value = ... because we observe that the current syntax is too confusing.