Fix migration edge cases with MySQL and PostgreSQL

evennia/comms/migrations/0013_auto_20170705_1726.py

@@ -3,17 +3,11 @@
 from __future__ import unicode_literals
 
 from django.db import migrations, models, connection
-from django.db import OperationalError
 
 
 def _table_exists(db_cursor, tablename):
     "Returns bool if table exists or not"
-    sql_check_exists = "SELECT * from %s;" % tablename
-    try:
-        db_cursor.execute(sql_check_exists)
-        return True
-    except OperationalError:
-        return False
+    return tablename in connection.introspection.table_names()
 
 
 class Migration(migrations.Migration):

evennia/comms/migrations/0015_auto_20170706_2041.py

@@ -2,17 +2,12 @@
 # Generated by Django 1.11.2 on 2017-07-06 20:41
 from __future__ import unicode_literals
 
-from django.db import migrations, OperationalError, connection
+from django.db import migrations, connection
 
 
 def _table_exists(db_cursor, tablename):
     "Returns bool if table exists or not"
-    sql_check_exists = "SELECT * from %s;" % tablename
-    try:
-        db_cursor.execute(sql_check_exists)
-        return True
-    except OperationalError:
-        return False
+    return tablename in connection.introspection.table_names()
 
 
 class Migration(migrations.Migration):

evennia/objects/migrations/0007_objectdb_db_account.py

@@ -2,10 +2,15 @@
 # Generated by Django 1.11.2 on 2017-07-05 17:27
 from __future__ import unicode_literals
 
-from django.db import migrations, models
+from django.db import migrations, models, connection
 import django.db.models.deletion
 
 
+def _table_exists(db_cursor, tablename):
+    "Returns bool if table exists or not"
+    return tablename in connection.introspection.table_names()
+
+
 class Migration(migrations.Migration):
 
     dependencies = [
@@ -13,10 +18,15 @@ class Migration(migrations.Migration):
         ('objects', '0006_auto_20170606_1731'),
     ]
 
-    operations = [
-        migrations.AddField(
-            model_name='objectdb',
-            name='db_account',
-            field=models.ForeignKey(help_text=b'an Account connected to this object, if any.', null=True, on_delete=django.db.models.deletion.SET_NULL, to='accounts.AccountDB', verbose_name=b'account'),
-        ),
-    ]
+    db_cursor = connection.cursor()
+    operations = []
+    if _table_exists(db_cursor, "players_playerdb"):
+        # OBS - this is run BEFORE migrations even start, so if we have a player table
+        # here we are not starting from scratch.
+        operations = [
+            migrations.AddField(
+                model_name='objectdb',
+                name='db_account',
+                field=models.ForeignKey(help_text=b'an Account connected to this object, if any.', null=True, on_delete=django.db.models.deletion.SET_NULL, to='accounts.AccountDB', verbose_name=b'account'),
+            ),
+        ]

evennia/objects/migrations/0009_remove_objectdb_db_player.py

@@ -3,17 +3,11 @@
 from __future__ import unicode_literals
 
 from django.db import migrations, connection
-from django.db import OperationalError
 
 
 def _table_exists(db_cursor, tablename):
     "Returns bool if table exists or not"
-    sql_check_exists = "SELECT * from %s;" % tablename
-    try:
-        db_cursor.execute(sql_check_exists)
-        return True
-    except OperationalError:
-        return False
+    return tablename in connection.introspection.table_names()
 
 
 class Migration(migrations.Migration):

evennia/scripts/migrations/0009_scriptdb_db_account.py

@@ -2,10 +2,15 @@
 # Generated by Django 1.11.2 on 2017-07-05 17:27
 from __future__ import unicode_literals
 
-from django.db import migrations, models
+from django.db import migrations, models, connection
 import django.db.models.deletion
 
 
+def _table_exists(db_cursor, tablename):
+    "Returns bool if table exists or not"
+    return tablename in connection.introspection.table_names()
+
+
 class Migration(migrations.Migration):
 
     dependencies = [
@@ -13,10 +18,15 @@ class Migration(migrations.Migration):
         ('scripts', '0008_auto_20170606_1731'),
     ]
 
-    operations = [
-        migrations.AddField(
-            model_name='scriptdb',
-            name='db_account',
-            field=models.ForeignKey(blank=True, help_text=b'the account to store this script on (should not be set if db_obj is set)', null=True, on_delete=django.db.models.deletion.CASCADE, to='accounts.AccountDB', verbose_name=b'scripted account'),
-        ),
-    ]
+    db_cursor = connection.cursor()
+    operations = []
+    if _table_exists(db_cursor, "players_playerdb"):
+        # OBS - this is run BEFORE migrations even start, so if we have a player table
+        # here we are not starting from scratch.
+        operations = [
+            migrations.AddField(
+                model_name='scriptdb',
+                name='db_account',
+                field=models.ForeignKey(blank=True, help_text=b'the account to store this script on (should not be set if db_obj is set)', null=True, on_delete=django.db.models.deletion.CASCADE, to='accounts.AccountDB', verbose_name=b'scripted account'),
+            ),
+        ]

evennia/scripts/migrations/0011_remove_scriptdb_db_player.py

@@ -2,17 +2,12 @@
 # Generated by Django 1.11.2 on 2017-07-06 20:41
 from __future__ import unicode_literals
 
-from django.db import migrations, OperationalError, connection
+from django.db import migrations, connection
 
 
 def _table_exists(db_cursor, tablename):
     "Returns bool if table exists or not"
-    sql_check_exists = "SELECT * from %s;" % tablename
-    try:
-        db_cursor.execute(sql_check_exists)
-        return True
-    except OperationalError:
-        return False
+    return tablename in connection.introspection.table_names()
 
 
 class Migration(migrations.Migration):

evennia/typeclasses/migrations/0010_delete_old_player_tables.py

@@ -2,17 +2,12 @@
 # Generated by Django 1.11.3 on 2017-07-13 18:47
 from __future__ import unicode_literals
 
-from django.db import migrations, OperationalError, connection
+from django.db import migrations, connection
 
 
 def _table_exists(db_cursor, tablename):
     "Returns bool if table exists or not"
-    sql_check_exists = "SELECT * from %s;" % tablename
-    try:
-        db_cursor.execute(sql_check_exists)
-        return True
-    except OperationalError:
-        return False
+    return tablename in connection.introspection.table_names()
 
 
 def _drop_table(db_cursor, table_name):