hopsor / money

Elixir library for working with Money safer, easier, and fun... Is an interpretation of the Fowler's Money pattern in fun.prog.

Money

Elixir library for working with Money safer, easier, and fun, is an interpretation of the Martin Fowler's Money pattern in functional programming.

"If I had a dime for every time I've seen someone use FLOAT to store currency, I'd have $999.997634" -- Bill Karwin

In short: You shouldn't represent monetary values by a float. Wherever you need to represent money, use Money.

Installation

Money comes with no required dependencies.

Add the following to your mix.exs:

def deps do
  [{:money, "~> 1.12"}]
end

then run mix deps.get.

Usage

five_eur         = Money.new(500, :EUR)             # %Money{amount: 500, currency: :EUR}
ten_eur          = Money.add(five_eur, five_eur)    # %Money{amount: 10_00, currency: :EUR}
hundred_eur      = Money.multiply(ten_eur, 10)      # %Money{amount: 100_00, currency: :EUR}
ninety_nine_eur  = Money.subtract(hundred_eur, 100) # %Money{amount: 99_00, currency: :EUR}
shares           = Money.divide(ninety_nine_eur, 2) # [%Money{amount: 4950, currency: :EUR}, %Money{amount: 4950, currency: :EUR}]

Money.equals?(five_eur, Money.new(500, :EUR)) # true
Money.zero?(five_eur);                        # false
Money.positive?(five_eur);                    # true

Money.Currency.symbol(:USD)                   # $
Money.Currency.symbol(Money.new(500, :AFN))   # ؋
Money.Currency.name(Money.new(500, :AFN))     # Afghani

Money.to_string(Money.new(500, :CNY))         # ¥ 5.00
Money.to_string(Money.new(1_234_56, :EUR), separator: ".", delimiter: ",", symbol: false)
"1.234,56"
Money.to_string(Money.new(1_234_56, :USD), fractional_unit: false)  # "$1,234"
Money.to_string(Money.new(1_234_50, :USD), strip_insignificant_zeros: true)  # "$1,234.5"

Serialization to database with single currency

Bring Money to your Ecto project. The underlying database type is integer

1. Set a default currency in config.ex:

   config :money,
     default_currency: :USD

2. Create migration with integer type:

   create table(:jobs) do
     add :amount, :integer
   end

3. Create schema using the Money.Ecto.Amount.Type Ecto type (don't forget run mix ecto.migrate):

   schema "jobs" do
     field :amount, Money.Ecto.Amount.Type
   end

4. Save to the database:

   iex(1)> Repo.insert %Job{amount: Money.new(100, :USD)}
   [debug] QUERY OK db=90.7ms queue=0.1ms
   INSERT INTO "jobs" ("amount","inserted_at","updated_at") VALUES ($1,$2,$3) RETURNING "id" [100, {{2019, 2, 12}, {7, 29, 8, 589489}}, {{2019, 2, 12}, {7, 29, 8, 593185}}]
   {:ok,
    %MoneyTest.Offers.Job{
      __meta__: #Ecto.Schema.Metadata<:loaded, "jobs">,
      amount: %Money{amount: 100, currency: :USD},
      id: 1,
      inserted_at: ~N[2019-02-12 07:29:08.589489],
      updated_at: ~N[2019-02-12 07:29:08.593185]
    }}

5. Get from the database:

   iex(2)> Repo.one(Job, limit: 1)
   [debug] QUERY OK source="jobs" db=1.8ms
   SELECT j0."id", j0."amount", j0."inserted_at", j0."updated_at" FROM "jobs" AS j0 []
   %MoneyTest.Offers.Job{
     __meta__: #Ecto.Schema.Metadata<:loaded, "jobs">,
     amount: %Money{amount: 100, currency: :USD},
     id: 1,
     inserted_at: ~N[2019-02-12 07:29:08.589489],
     updated_at: ~N[2019-02-12 07:29:08.593185]
   }
   

Serialization to PostgreSQL with multiple currency

Money.Ecto.Composite.Type Ecto type represents serialization of Money.t to PostgreSQL Composite Types with saving currency.

1. Create migration with custom type:

   def up do
     execute """
     CREATE TYPE public.money_with_currency AS (amount integer, currency varchar(3))
     """
   end
   
   def down do
     execute """
     DROP TYPE public.money_with_currency
     """
   end

2. Then use created custom type(money_with_currency) for money field:

   def change do
     alter table(:jobs) do
       add :price, :money_with_currency
     end
   end

3. Create schema using the Money.Ecto.Composite.Type Ecto type (don't forget run mix ecto.migrate):

   schema "jobs" do
     field :price, Money.Ecto.Composite.Type
   end

4. Save to the database:

   iex(1)> Repo.insert %Job{price: Money.new(100, :JPY)}
   [debug] QUERY OK db=7.7ms
   INSERT INTO "jobs" ("price","inserted_at","updated_at") VALUES ($1,$2,$3) RETURNING "id" [{100, "JPY"}, {{2019, 2, 12}, {8, 7, 44, 729114}}, {{2019, 2, 12}, {8, 7, 44, 729124}}]
   {:ok,
    %MoneyTest.Offers.Job{
      __meta__: #Ecto.Schema.Metadata<:loaded, "jobs">,
      id: 6,
      inserted_at: ~N[2019-02-12 08:07:44.729114],
      price: %Money{amount: 100, currency: :JPY},
      updated_at: ~N[2019-02-12 08:07:44.729124]
    }}

5. Get from the database:

   iex(2)> Repo.one(Job, limit: 1)
   [debug] QUERY OK source="jobs" db=1.4ms
   SELECT j0."id", j0."price", j0."inserted_at", j0."updated_at" FROM "jobs" AS j0 []
   %MoneyTest.Offers.Job{
     __meta__: #Ecto.Schema.Metadata<:loaded, "jobs">,
     id: 6,
     inserted_at: ~N[2019-02-12 08:07:44.729114],
     price: %Money{amount: 100, currency: :JPY},
     updated_at: ~N[2019-02-12 08:07:44.729124]
   }
   

Serialization to database (JSON) with multiple currency

Money.Ecto.Map.Type Ecto type represents serialization of Money.t to map(JSON) with saving currency.

1. Create migration with map type:

   def change do
     alter table(:jobs) do
       add :price, :map
     end
   end

2. Create schema using the Money.Ecto.Map.Type Ecto type (don't forget run mix ecto.migrate):

   schema "jobs" do
     field :price, Money.Ecto.Map.Type
   end

3. Save to the database:

   iex(1)> Repo.insert %Job{price: Money.new(100, :JPY)}
   [debug] QUERY OK db=4.6ms
   INSERT INTO "jobs" ("price","inserted_at","updated_at") VALUES ($1,$2,$3) RETURNING "id" [%{"amount" => 100, "currency" => "JPY"}, {{2019, 2, 26}, {9, 40, 14, 381721}}, {{2019, 2, 26}, {9, 40, 14, 381730}}]
   {:ok,
    %MoneyTest.Offers.Job{
      __meta__: #Ecto.Schema.Metadata<:loaded, "jobs">,
      id: 9,
      inserted_at: ~N[2019-02-26 09:40:14.381721],
      price: %Money{amount: 100, currency: :JPY},
      updated_at: ~N[2019-02-26 09:40:14.381730]
    }}

4. Get from the database:

   iex(8)> Repo.one(Job, limit: 1)
   [debug] QUERY OK source="jobs" db=2.0ms
   SELECT j0."id", j0."price", j0."inserted_at", j0."updated_at" FROM "jobs" AS j0 []
   %MoneyTest.Offers.Job{
     __meta__: #Ecto.Schema.Metadata<:loaded, "jobs">,
     id: 10,
     inserted_at: ~N[2019-02-26 09:40:45.205076],
     price: %Money{amount: 100, currency: :JPY},
     updated_at: ~N[2019-02-26 09:40:45.205084]
   }
   

Money.Sigils

# Sigils for Money
import Money.Sigils

iex> ~M[1000]USD
%Money{amount: 1000, currency: :USD}

# If you have a default currency configured (e.g. to GBP), you can do
iex> ~M[1000]
%Money{amount: 1000, currency: :GBP}

Money.Currency

# Currency convenience methods
import Money.Currency, only: [usd: 1, eur: 1, afn: 1]

iex> usd(100_00)
%Money{amount: 10000, currency: :USD}
iex> eur(100_00)
%Money{amount: 10000, currency: :EUR}
iex> afn(100_00)
%Money{amount: 10000, currency: :AFN}

Money.Currency.symbol(:USD)     # $
Money.Currency.symbol(afn(500)) # ؋
Money.Currency.name(afn(500))   # Afghani
Money.Currency.get(:AFN)        # %{name: "Afghani", symbol: "؋"}

Phoenix.HTML.Safe

Bring Money to your Phoenix project. If you are using Phoenix, you can include money objects directly into your output and they will be correctly escaped.

<b><%= Money.new(12345,67, :GBP) %></b>

Configuration

You can set a default currency and default formatting preferences as follows:

config :money,
  default_currency: :EUR,
  separator: ".",
  delimiter: ",",
  symbol: false,
  symbol_on_right: false,
  symbol_space: false,
  fractional_unit: true,
  strip_insignificant_zeros: false,
  code: false,
  minus_sign_first: true,
  strip_insignificant_fractional_unit: false

Then you don’t have to specify the currency.

iex> amount = Money.new(1_234_50)
%Money{amount: 123450, currency: :EUR}
iex> to_string(amount)
"1.234,50"

Here is another example of formatting money:

iex> amount = Money.new(1_234_50)
%Money{amount: 123450, currency: :EUR}
iex> Money.to_string(amount, symbol: true, symbol_on_right: true, symbol_space: true)
"1.234,50 €"

Custom Currencies

In some cases we can need to add not common currencies, like crypto currencies or others. In order to add your own currencies you have to add them in the config file following this format:

config :money,
  custom_currencies: [
    BTC: %{name: "Bitcoin", symbol: "₿", exponent: 8},
    GCS: %{name: "Galactic Credit Standard", symbol: "gcs", exponent: 0}
  ]

Troubleshooting

Validating amount in Ecto changeset

When using the Money.Ecto.Amount.Type type, it may seem that a simple value validation should work, for example:

schema "jobs" do
  field :amount, Money.Ecto.Amount.Type
end

def changeset(struct, params \\ %{}) do
  struct
  |> cast(params, [:amount])
  |> validate_number(:amount, [greater_than: 0])
end

But this kind of validation will not work, since under the hood Money.Ecto.Amount.Type has the structure %Money{amount: ..., currency: ...}. To validate the data in this case, we recommend adding custom validation that matches your logic.

Example:

def changeset(struct, params \\ %{}) do
  struct
  |> cast(params, [:amount])
  |> validate_money(:amount)
end

defp validate_money(changeset, field) do
  validate_change(changeset, field, fn
    _, %Money{amount: amount} when amount > 0 -> []
    _, _ -> [amount: "must be greater than 0"]
  end)
end

Lack of precision when using Money.parse

Sometimes you need to work with large numbers (for example, cryptocurrencies) and Float precision is not enough. In this case it is better to use Decimal package. Money already has support for Decimal and you just need to add it to your project dependencies.

License

MIT License please see the LICENSE.md file.