Create a currency model

InvenTree/common/models.py

@@ -1,3 +1,79 @@
-from django.db import models
+"""
+Common database model definitions.
+These models are 'generic' and do not fit a particular business logic object.
+"""
 
-# Create your models here.
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models
+from django.utils.translation import ugettext as _
+from django.core.validators import MinValueValidator, MaxValueValidator
+
+
+class Currency(models.Model):
+    """
+    A Currency object represents a particular unit of currency.
+    Each Currency has a scaling factor which relates it to the base currency.
+    There must be one (and only one) currency which is selected as the base currency,
+    and each other currency is calculated relative to it.
+
+    Attributes:
+        symbol: Currency symbol e.g. $
+        suffix: Currency suffix e.g. AUD
+        description: Long-form description e.g. "Australian Dollars"
+        value: The value of this currency compared to the base currency.
+        base: True if this currency is the base currency
+
+    """
+
+    symbol = models.CharField(max_length=10, blank=False, unique=False, help_text=_('Currency Symbol e.g. $'))
+
+    suffix = models.CharField(max_length=10, blank=False, unique=True, help_text=_('Currency Suffix e.g. AUD'))
+
+    description = models.CharField(max_length=100, blank=False, help_text=_('Currency Description'))
+
+    value = models.DecimalField(max_digits=10, decimal_places=5, validators=[MinValueValidator(0.00001), MaxValueValidator(100000)], help_text=_('Currency Value'))
+
+    base = models.BooleanField(default=False, help_text=_('Use this currency as the base currency'))
+
+    class Meta:
+        verbose_name_plural = 'Currencies'
+
+    def __str__(self):
+        """ Format string for currency representation """
+        s = "{sym} {suf} - {desc}".format(
+            sym=self.symbol,
+            suf=self.suffix,
+            desc=self.description
+        )
+
+        if self.base:
+            s += " (Base)"
+        
+        else:
+            s += " = {v}".format(v=self.value)
+
+        return s
+
+    def save(self, *args, **kwargs):
+        """ Validate the model before saving
+
+        - Ensure that there is only one base currency!
+        """
+
+        # If this currency is set as the base currency, ensure no others are
+        if self.base:
+            for cur in Currency.objects.filter(base=True).exclude(pk=self.pk):
+                cur.base = False
+                cur.save()
+
+        # If there are no currencies set as the base currency, set this as base
+        if not Currency.objects.filter(base=True).exists():
+            self.base = True
+
+        # If this is the base currency, ensure value is set to unity
+        if self.base:
+            self.value = 1.0
+
+        super().save(*args, **kwargs)