How to get a contract storage data or call a "get" entrypoint from another contract in smartPy?

Question

I want to interact with the FA12.py smart contract (https://smartpy.io/demo/index.html?template=FA1.2.py) and get the balance of a user, from another smart contract.

the FA12 function that I tried to call :

@sp.entry_point 
def getBalance(self, params): 
    sp.transfer(
        sp.as_nat(self.data.balances[params.arg.owner].balance),
        sp.tez(0), 
        sp.contract(sp.TNat, params.target).open_some()
    )

What I tried to do from another contract:

@sp.entry_point
def getFA12Balance(self, params):
    assertTrasnferRecord = sp.TRecord(arg = sp.TRecord(owner = params.owner), target = params.address)
    entryPointName = "getBalance"
    c = sp.contract(
        t = sp.TNat,
        address = self.data.FA12Address,
        entry_point = entryPointName
    ).open_some()

    sp.transfer(assertTrasnferRecord, sp.mutez(0), c)

The answer I get :

Error: Error in Scenario 
Literal format error: (record(record((arg(record((owner(attr(params 186)owner 187)))None))(target(attr(params 186)address 187)))None))

**** EDIT ****

after fixing the format error based on FFF answer:

def getBalance(self, params):
    assertTrasnferRecord = sp.record(arg = sp.record(owner = params.owner), target = params.address)
    entryPointName = "getBalance"
    c = sp.contract(
        t = sp.TRecord(arg = sp.TRecord(owner = sp.TAddress), target = sp.TAddress),
        address = self.data.FA12Address,
        entry_point = entryPointName
    ).open_some()

    call(assertTrasnferRecord, c)

I'm still have an error when testing the function with smartpy as follows :

c2.getBalance(owner = alice.address, address = c2.address).run(sender = admin)

Error text :

Error: Error in Scenario
Unexpected error in transaction, please use .run(valid=False, ..)
ChannelNotFound: 'default'
default (18 : sp.TNat)

Answer 1

    assertTrasnferRecord = sp.TRecord(arg = sp.TRecord(owner = params.owner), target = params.address)

You're building a type sp.TRecord and put a value inside params.owner. This is not well built which leads to a Literal format error.

Instead of using sp.TRecord, you should try sp.record to build an expression (not a type).

Answer 2

In addition to FFF answer the type of your entry point is not “sp.TNat” so i expect after you fixed the first error he showed you will get another typing error.

When you call “open_some” you are expected to provide full specification of the entry point argument type. Please see

https://www.smartpy.io/dev/reference.html#_contract_and_address