Improve error handling and data type safety in DBManager; ensure numeric columns are converted to float and handle missing config values gracefully

app.py

@@ -12,7 +12,11 @@ model_mgr = ModelManager('model_ai_bta.pkl', 'laju_penipisan.pkl')
 # ==================== UTILITY FUNCTIONS ====================
 
 def get_min_safe_thickness():
-    return float(db.get_config('min_safe_thickness'))
+    try:
+        val = db.get_config('min_safe_thickness')
+        return float(val) if val else 115.0
+    except:
+        return 115.0
 
 def get_initial_empty_state():
     """Return empty state untuk initial load"""

db_manager.py

@@ -101,7 +101,12 @@ class DBManager:
             ''')
             row = cursor.fetchone()
             if row:
-                return dict(row)
+                result = dict(row)
+                # Ensure numeric columns are float
+                for col in ['cone_depan', 'bodi_tengah', 'cone_belakang', 'suhu_avg', 'ketebalan_actual', 'ketebalan_prediksi']:
+                    if col in result and result[col] is not None:
+                        result[col] = float(result[col])
+                return result
             return None
     
     def get_historis(self, limit=100, flagged_only=False):
@@ -123,7 +128,15 @@ class DBManager:
             
             cursor.execute(query, (limit,))
             rows = cursor.fetchall()
-            return [dict(row) for row in rows]
+            results = []
+            for row in rows:
+                result = dict(row)
+                # Ensure numeric columns are float
+                for col in ['cone_depan', 'bodi_tengah', 'cone_belakang', 'suhu_avg', 'ketebalan_actual', 'ketebalan_prediksi']:
+                    if col in result and result[col] is not None:
+                        result[col] = float(result[col])
+                results.append(result)
+            return results
     
     def get_all_data_as_dataframe(self):
         """Get all measurement data sebagai Pandas DataFrame"""
@@ -163,7 +176,11 @@ class DBManager:
             cursor = conn.cursor()
             cursor.execute("SELECT value FROM app_config WHERE key = ?", (key,))
             row = cursor.fetchone()
-            return row[0] if row else None
+            value = row[0] if row else None
+            # Ensure string type
+            if value is not None and isinstance(value, bytes):
+                value = value.decode('utf-8')
+            return value
     
     def set_config(self, key, value):
         """Set config value"""
@@ -194,7 +211,7 @@ class DBManager:
                 ORDER BY timestamp DESC LIMIT 1
             ''')
             latest = cursor.fetchone()
-            current_thickness = latest[0] if latest else 230
+            current_thickness = float(latest[0]) if latest else 230.0
             
             # Total maintenance events
             cursor.execute("SELECT COUNT(*) FROM maintenance_log")