Specs

get_account!(uuid()) :: account()

Gets a single account and associated transactions.

Examples

iex> get_account!("9b8dfc93-f59d-4de7-af60-57c535501ba9")
%Account{
  current_balance: 0.0,
  transactions_in: [],
  transactions_out: [],
  uuid: "9b8dfc93-f59d-4de7-af60-57c535501ba9"
}

Specs

new_account(map()) :: {:ok, account()} | {:error, changeset()}

Creates an account.

Examples

iex> new_account(%{current_balance: 10})
{:ok,
 %Account{
   current_balance: 10.0,
   uuid: "b92a8690-fb6e-425d-87f5-ea6ae16af83d",
   # ...
 }}

iex> new_account(%{current_balance: -10})
{:error, %Ecto.Changeset{}}

Specs

transfer_money(uuid(), uuid(), float()) ::
  {:ok, transaction()} | {:error, keyword()}

Transfers the specified amount between the given accounts.

In practice, this function creates a transaction data and updates the accounts. If the sender account doesn't have the specified amount, it will rollback the transaction and restore the database to the previous state.

Examples

Lets start with a sender account, with an opening balance of 100.0, and an address account with 0.0.

iex> {:ok, sender} = new_account(%{current_balance: 100})
iex> {:ok, address} = new_account(%{current_balance: 0})

Now we transfer 30.0 from sender to address.

iex> transfer_money(sender.uuid, address.uuid, 30)
# begin []
# INSERT INTO "transactions" ...
# UPDATE "accounts" ...
# UPDATE "accounts" ...
# commit []
{:ok,
 %GraphBanking.Transaction{
   address_uuid: "3c11de5c-da6d-4a90-8d82-8432b1e4061f",
   amount: 30.0,
   sender_uuid: "d5cb1878-9fd4-4adc-8a44-2af0035de952",
   uuid: "d3020427-0b62-495e-b9f1-5d3160d77e84",
   when: ~U[2020-11-20 18:51:10Z],
   # ...
 }}

If we check the current balance on both accounts we can see that it changed.

iex> get_account!(sender.uuid)
%GraphBanking.Account{
  current_balance: 70.0,
  uuid: "d5cb1878-9fd4-4adc-8a44-2af0035de952",
  # ...
}
iex> get_account!(address.uuid)
%GraphBanking.Account{
  current_balance: 30.0,
  uuid: "3c11de5c-da6d-4a90-8d82-8432b1e4061f",
  # ...
}

We have now 70.0 on sender and 30.0 on address.

If we try to transfer again, but now the amount of 100.0, we can see that it returns an error because sender has only 70.0 available on the account.

iex> transfer_money(sender.uuid, address.uuid, 100)
# begin []
# INSERT INTO "transactions" ...
# UPDATE "accounts" ...
# UPDATE "accounts" ...
# rollback []
{:error, [current_balance: "can't be negative"]}

The error states that the account can't have a negative balance and this constraint triggers the transaction rollback.