Fix handling of prefixed Asset IDs and sorting of the asset list (#382)

* FIX: Remove misleading admin site title

* Moved across assets_id sorting to use proper numeric values. Also mofifies SQL command to find free asset IDs so that it works on postgres.

* Changed generateSampleAssetsData.py to include prefices on some cables.

* Fixed pep8

* Fixed missed migration

* Ensured hidden asset fields are completed on every database write

* CMULTI is a thing, and therefore a max prefix length of 5 cannot be a thing

assets/models.py

@@ -3,6 +3,9 @@ from django.core.exceptions import ValidationError
 from django.db import models, connection
 from django.urls import reverse
 
+from django.db.models.signals import pre_save
+from django.dispatch.dispatcher import receiver
+
 
 class AssetCategory(models.Model):
     class Meta:
@@ -54,14 +57,14 @@ class Connector(models.Model):
 
 class Asset(models.Model):
     class Meta:
-        ordering = ['asset_id']
+        ordering = ['asset_id_prefix', 'asset_id_number']
         permissions = (
             ('asset_finance', 'Can see financial data for assets'),
             ('view_asset', 'Can view an asset')
         )
 
     parent = models.ForeignKey(to='self', related_name='asset_parent', blank=True, null=True, on_delete=models.SET_NULL)
-    asset_id = models.CharField(max_length=10, unique=True)
+    asset_id = models.CharField(max_length=15, unique=True)
     description = models.CharField(max_length=120)
     category = models.ForeignKey(to=AssetCategory, on_delete=models.CASCADE)
     status = models.ForeignKey(to=AssetStatus, on_delete=models.CASCADE)
@@ -83,18 +86,24 @@ class Asset(models.Model):
     circuits = models.IntegerField(blank=True, null=True)
     cores = models.IntegerField(blank=True, null=True)
 
-    def get_available_asset_id():
+    # Hidden asset_id components
+    # For example, if asset_id was "C1001" then asset_id_prefix would be "C" and number "1001"
+    asset_id_prefix = models.CharField(max_length=8, default="")
+    asset_id_number = models.IntegerField(default=1)
+
+    def get_available_asset_id(wanted_prefix=""):
         sql = """
-        SELECT MIN(CAST(a.asset_id AS int))+1
+        SELECT a.asset_id_number+1
         FROM assets_asset a
         LEFT OUTER JOIN assets_asset b ON
-            (CAST(a.asset_id AS int) + 1 = CAST(b.asset_id AS int))
-        WHERE b.asset_id IS NULL AND CAST(a.asset_id AS int) >= %s;
+            (a.asset_id_number + 1 = b.asset_id_number AND
+            a.asset_id_prefix = b.asset_id_prefix)
+        WHERE b.asset_id IS NULL AND a.asset_id_number >= %s AND a.asset_id_prefix = %s;
         """
         with connection.cursor() as cursor:
-            cursor.execute(sql, [9000])
+            cursor.execute(sql, [9000, wanted_prefix])
             row = cursor.fetchone()
-            if row[0] is None:
+            if row is None or row[0] is None:
                 return 9000
             else:
                 return row[0]
@@ -114,8 +123,9 @@ class Asset(models.Model):
             errdict["date_sold"] = ["Cannot sell an item before it is acquired"]
 
         self.asset_id = self.asset_id.upper()
-        if re.search("^[a-zA-Z0-9]+$", self.asset_id) is None:
-                errdict["asset_id"] = ["An Asset ID can only consist of letters and numbers"]
+        asset_search = re.search("^([a-zA-Z0-9]*?[a-zA-Z]?)([0-9]+)$", self.asset_id)
+        if asset_search is None:
+                errdict["asset_id"] = ["An Asset ID can only consist of letters and numbers, with a final number"]
 
         if self.purchase_price and self.purchase_price < 0:
             errdict["purchase_price"] = ["A price cannot be negative"]
@@ -139,3 +149,14 @@ class Asset(models.Model):
 
         if errdict != {}:  # If there was an error when validation
             raise ValidationError(errdict)
+
+
+@receiver(pre_save, sender=Asset)
+def pre_save_asset(sender, instance, **kwargs):
+    """Automatically fills in hidden members on database access"""
+    asset_search = re.search("^([a-zA-Z0-9]*?[a-zA-Z]?)([0-9]+)$", instance.asset_id)
+    if asset_search is None:
+        instance.asset_id += "1"
+    asset_search = re.search("^([a-zA-Z0-9]*?[a-zA-Z]?)([0-9]+)$", instance.asset_id)
+    instance.asset_id_prefix = asset_search.group(1)
+    instance.asset_id_number = int(asset_search.group(2))