Creating ArrayField of custom basefield in Django

models.py

from moneyed import Money
from psycopg2.extras import register_composite
from psycopg2.extensions import register_adapter, adapt, AsIs

MoneyValue = register_composite(
    'money_value',
    connection.cursor().cursor,
    globally=True
).type

def moneyvalue_adapter(value):
    return AsIs("(%s,%s)::money_value" % (
        adapt(value.amount),
        adapt(value.currency.code)))

register_adapter(Money, moneyvalue_adapter)

class MoneyValueField(models.Field):
    description = "wrapper for money_value composite type in postgres"
    
    def from_db_value(self,value,expression,connection):
        if value is None:
            return value
        return Money(value.amount,value.currency)
        
    def to_python(self,value):
        if isinstance(value,Money):
            return value
        if value is None:
            return value
        return Money(value.amount,value.currency.code)

    def get_prep_value(self, value):
        # in input box we enter 10 USD,20 INR,30 AUD
        amount,currency = value.split()
        return Money(decimal.Decimal(amount),currency)
        
    def db_type(self,connection):
        return 'money_value'

 class Transaction(models.Model)
    amount = MoneyValueField()
  
 class Balance(models.Model)
    bal = ArrayField(MoneyValueField(),size = 3)