diff --git a/advlabdb/models.py b/advlabdb/models.py
index 3891da3..1f1fb24 100644
--- a/advlabdb/models.py
+++ b/advlabdb/models.py
@@ -57,6 +57,23 @@ class PartStudent(db.Model):
         db.UniqueConstraint(student_id, group_id),
     )
 
+    def check(group, part):
+        if group and group.program != part.program:
+            raise DataBaseException(
+                f"Group's program {group.program} and student part's program {part.program} do not match!"
+            )
+
+    def customInit(student, part, group=None):
+        PartStudent.check(group, part)
+
+        return PartStudent(student=student, part=part, group=group)
+
+    def customUpdate(self, group, final_part_mark):
+        Part.check(group, self.part)
+
+        self.group = group
+        self.final_part_mark = final_part_mark
+
     def repr(self):
         return f"{self.student.repr()} {self.part.repr()}"
 
@@ -76,30 +93,46 @@ class Group(db.Model):
 
     __table_args__ = (db.UniqueConstraint(number, semester_id, program_id),)
 
-    def checkPartStudents(partStudents):
-        if partStudents:
-            program = partStudents[0].part.program
-            semester = partStudents[0].part.semester
-            for partStudent in partStudents[1:]:
-                if partStudent.part.program != program:
-                    raise DataBaseException(f"Part Students {partStudents} are not in the same program!")
+    def check(part_students, program=None):
+        commonProgram = part_students[0].part.program
+        if program and program != commonProgram:
+            raise DataBaseException("Group's program and students' program mismatch!")
 
-                if partStudent.part.semester != semester:
-                    raise DataBaseException(f"Part Students {partStudents} are not in the same semester!")
+        commonSemester = part_students[0].part.semester
 
-    def customInit(semester, program, partStudents):
-        checkPartStudents(partStudents)
+        for partStudent in part_students[1:]:
+            if partStudent.part.program != commonProgram:
+                raise DataBaseException(f"Part Students {part_students} are not in the same program!")
 
-        orderedGroups = Group.query.filter(Group.semester == semester, Group.program == program).order_by(Group.number)
-        lastTakenGroupNumber = orderedGroups[-1].number if orderedPartGroups.count() > 0 else 0
+            if partStudent.part.semester != commonSemester:
+                raise DataBaseException(f"Part Students {part_students} are not in the same semester!")
+
+    def customInit(part_students):
+        Group.check(part_students)
+
+        semester = part_students[0].part.semester
+        program = part_students[0].part.program
+
+        lastTakenGroupNumber = (
+            Group.query.filter(Group.semester == semester, Group.program == program)
+            .order_by(Group.number.desc())
+            .first()
+            .number
+            or 0
+        )
 
         return Group(
             program=program,
             number=lastTakenGroupNumber + 1,
-            part_students=partStudents,
+            part_students=part_students,
             semester=semester,
         )
 
+    def customUpdate(self, part_students):
+        Group.check(part_students, self.program)
+
+        self.part_students = part_students
+
     def repr(self):
         return f"{self.number} {self.program.repr()} {self.semester.repr()}"
 
@@ -169,7 +202,7 @@ class Experiment(db.Model):
         nullable=False,
     )
     final_weighting = db.Column(
-        db.Float, db.CheckConstraint("final_weighting >= 0"), db.CheckConstraint("final_weightin <= 1"), nullable=False
+        db.Float, db.CheckConstraint("final_weighting >= 0"), db.CheckConstraint("final_weighting <= 1"), nullable=False
     )
 
     program_id = db.Column(db.Integer, db.ForeignKey("program.id"), nullable=False)
@@ -263,23 +296,23 @@ class Appointment(db.Model):
 
         return assistant
 
-    def customInit(date, special, assistant, groupExperiment):
-        assistant = Appointment.checkAndGetAssistant(assistant, groupExperiment)
+    def customInit(date, special, assistant, group_experiment):
+        assistant = Appointment.checkAndGetAssistant(assistant, group_experiment)
 
         return Appointment(
             date=date,
             special=special,
-            group_experiment=groupExperiment,
+            group_experiment=group_experiment,
             assistant=assistant,
         )
 
-    def customUpdate(self, date, special, assistant, groupExperiment):
-        assistant = Appointment.checkAndGetAssistant(assistant, groupExperiment)
+    def customUpdate(self, date, special, assistant, group_experiment):
+        assistant = Appointment.checkAndGetAssistant(assistant, group_experiment)
 
         self.date = date
         self.special = special
         self.assistant = assistant
-        self.group_experiment = groupExperiment
+        self.group_experiment = group_experiment
 
     def repr(self):
         return f"{self.date} {self.group_experiment.repr()}"