fix: Adjust relationship between ServerGroup and Server

- Adjusting relationship
  - Server has one ServerGroup not servers
  - Using back_populates instead of backref for better control

- Adjusted references to ServerGroup in server:
  server.servergroup.name instead server.servers.name

Author: Luiz Matsumura

web/pgadmin/model/__init__.py

@@ -252,7 +252,12 @@ class ServerGroup(db.Model, UserScopedMixin):
     name = db.Column(db.String(128), nullable=False)
     __table_args__ = (db.UniqueConstraint('user_id', 'name'),)
 
-    servers = db.relationship('Server', backref='servergroup', lazy='select')
+    servers = db.relationship(
+        'Server',
+        back_populates='servergroup',
+        lazy='select',
+        cascade=CASCADE_STR
+    )
 
     @property
     def serialize(self):
@@ -295,9 +300,9 @@ class Server(db.Model, UserScopedMixin):
     role = db.Column(db.String(64), nullable=True)
     comment = db.Column(db.String(1024), nullable=True)
     discovery_id = db.Column(db.String(128), nullable=True)
-    servers = db.relationship(
+    servergroup = db.relationship(
         'ServerGroup',
-        backref=db.backref('server', cascade=CASCADE_STR),
+        back_populates='servers',
         lazy='joined'
     )
     db_res = db.Column(db.Text(), nullable=True)

web/pgadmin/tools/schema_diff/__init__.py

@@ -307,10 +307,10 @@ def servers():
                 "connected": connected
             }
 
-            if server.servers.name in res:
-                res[server.servers.name].append(server_info)
+            if server.servergroup.name in res:
+                res[server.servergroup.name].append(server_info)
             else:
-                res[server.servers.name] = [server_info]
+                res[server.servergroup.name] = [server_info]
 
     except Exception as e:
         app.logger.exception(e)

web/pgadmin/tools/sqleditor/__init__.py

@@ -2420,7 +2420,7 @@ def get_new_connection_data(sgid=None, sid=None):
             manager = driver.connection_manager(server.id)
             conn = manager.connection()
             connected = conn.connected()
-            server_group_data[server.servers.name].append({
+            server_group_data[server.servergroup.name].append({
                 'label': server.name,
                 "value": server.id,
                 'image': server_icon_and_background(connected, manager,