diff --git a/DB.drawio b/DB.drawio
index eaabc3a..4cfcca3 100644
--- a/DB.drawio
+++ b/DB.drawio
@@ -1 +1 @@
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\ No newline at end of file
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D0w2YNgi2xpS04mePBTYhypD1m0f0G7JHV1VP9MFVhzYS9U+2PIo0zgJ12RYcj7V0pRBzby6kzPkNYlcg+R7Y6sRuW147V3GpxeSp1qS9Pk5lcpbJESCHqy9MAtS5xWeKVLAUvB6zkqPxps5XlQMkLcICAyl4EyPh1X767jke/WZlT3QsiekOFio3SO/MwiN6gleCltwaM/abmdCIli4XZmtJ4OkiaiDic40/SPIcDEak2IQwMGlwO/9TIoDFg76Sb+3eqORKhKSW2nGQA4kJxA620ARxZDtOgAZjm/p/qmafqP5Natdi1iFN/EEd8fyu2d3juI74rIThUUTeTiRZDSlrfAMyi8hzkmzbkJ4ELjQvl8EtwxfyzUJpTwIW2geKgArhCPkBKJ4AFiRTLwIduzCdGHlUTA+gmB17CxyE5XZAlmFZoGnj5DMwlpjxIHQLGQmsaqoYH102OvoSVQeOUQWpe45qnBi8xb5waIbqyTNEwWqM+/2gg3ejcyxx14MOgdzJTWkPV5z9njXzc0l6sDUTqzqSVBYqG0R1pUSkHo9sfcgl0qJSa0bj6U+askd/+7MQ8ZnbwRJw+VahoOF1iRBKdJz+oD1XOkxduy0pXTzA1PdA4F1HnmJhj4NHjZf8WpU/UMmUYWXODhqon1COL5xo8UHtSBynEeg+VDRVFjEurPdOPI1PnLum9bpbT+2OP0w4YJpi94tO07PvTdYk6TAtXVPJOxvs5P4i6eKkPFS+BrTXZbjnCvA+9G4G8LlYvZXaFcowBvGTeF5W7fknHH8jTeR+KKphECRXLCIOejpHKXQzdHU/l1gcW9IyWzbnNOF0PP4F7PIEnbrAMh3N75tDYZEHSxYJi3SIUt4XiJkcRwIkfRWIUp5qPGMXABGvPJhKLFS4WEhvdOHklB5rBKqRm2Vy199W7grWB/+iVwZ+9Wkyj73k4X80e4nDuDq9NwvWp4kWDazqHhQjXUEFSs7iu2uzqfeEa/0ksoJ5w5j+4njMkaouXMhZqA2WDRO3WqF06YVybOmgV1eFdUdssXwLQGrX5BH/gx18kBUOEyBUNp0uUkRKnG+J0Jvr2OF01Nva+OF3+wEZrnOajVw8r1xtHFCRWC5ItFlancyoJzS2g2WgbzTof9pS6p4F+Ujf+Zmvs+NDlaukE1NKgukixMHnQJya3xuR+20we8AZ+JzGSU2NAjGRgEinQF4yOx54oVixYzsoKKK6BANQ6cLivWVCrGp+PkJnUW/vAi2o1NVlqNSNWoGggbVJpByJIt36MUDV550xqSJv4qzuyMbzUa0a8UNGAWi1RdEXDeg5rRJVpVTmSOXZYT3vtZgbWiW03dGZYj6qW7LshrN8M0O6AgVwu46jjxQkdL1RWTcH2MFC/rayvTA0NirtRKtHFnhfqEWfr85teNNyADeigIHfXi62FIPZXdb5ggvpeCBNrQXfEuibp5nRHpPgvIlgDvTCa7pZZtR79fUUWMvNATGqDD//6ge1t3G2qn6goVjyk7kYrOUlIDcUDGiZ11W3WOyM1/kZGKtBRYRH4oR/ZJtFaiGjR0BqoQiVat0ZrqHtG01EQPocrdVny1kIQA1vn8zmxZIbLcDWmsZhihIsG2UC/FEJ2e8gGOmg07WETsnMsBDGygb4nm/mYNM1YqIDRYJtOZqPCNtBCo+nBfPwuW25sd+B4tgqcz86mpBCvBUgWDa/L9JGsqfotK3A7rvrtqFlVB8dpOd7DeoWxzNyR7QlSkLKDqtIk9eGSuXQPh3FUFTvJSWX1tWzNnMEs2mJnXgkaVaWqzHCiQfGoKu79mt7ArCoVaGdUt3HWY2QnmnyTxatmWUM0jjVEnTEOoF2OKEPsm+pv1mBfs63TTFHVFEble3XZIvMF6dohY9ThldVrjH3eGP9wvGgXu9aa2KvRlIkfv5rFRhZd9Lc/B0lR+XLqLnKdprkfxtayTKzZPOThqMq+vb9M3dC5j94Sf/wlsBfx9sleTp3xGcZqWfb5BJyLzzIFu3bRq80Z6h85oTNxWnc4m1zZ+9b3iAyC8AAG47t9tsNo0ztf30dT1B1UK7uo3gW1qmq/Gdbuf3bJ3c+o/nkdiFkXWDdO3cyqdrkLekqqpR3H3WQJG8t7dvYulicq70axvk0OBnlsGeydBuW8JHEE4339u81W7m8/Xqgd/W/ke6vZPI56aMrDKr26j69o5xf93/2X2wtvNHVmbwS0jaowjzGg95IKHYBi1UAgz0rkUErxLI81eZzLJ9aGTEoXyHTkGSVBvGGH4pbEjThI8GmW67sPG0xcrw/IRT/c7fPgg2s/BvbsTOt5sVE/RE5Q7zH+6WL8fGs/fLjktA6ybEZ/kBn5rhVbgBWLCNHcrHqPPfXnhx8f7cFV+M/bZPVxel6iBLiVQ4xVRofj2AeCfkbqXR50SNLp8Qf5UHqfVxEdBuNg9FhHuXQUZsDcSK2NQaDGa8dpPBxzEKHtm9+9G32veGg3DW+jUfjIjdhX1P6pcUdVZe7UK/nYrR54PBjsYCOPlthgx833L9bz0vi6uPkxcT+PDC84vz8vkcRtxgLFHZo/xm6bfN5YQOARlIl6nDva5JF5Jh5nsAfdy5ph32S2yIO6Qo6MuRvGIStkPiA6/u8uBg8/Zn+tXu56Tz8jjumrHz+O9fwaeg6eaIfH29Qplnu6HWYJtoMPQqvsxrCx56DG2E2fbSdQ2gD7B24kygDZRJ+pHDBA9gOqUi3oH70MfD/cfXu0C51+8sdO/I7/Bw==</diagram></mxfile>
\ No newline at end of file
diff --git a/advlabdb/modelViews.py b/advlabdb/modelViews.py
index 97bc7a9..35acdd5 100644
--- a/advlabdb/modelViews.py
+++ b/advlabdb/modelViews.py
@@ -4,7 +4,7 @@ from flask_admin.menu import MenuLink
 from flask_admin.model.template import EndpointLinkRowAction
 from flask_security import current_user, hash_password
 from sqlalchemy import func
-from wtforms import Form, BooleanField, SelectField, TextField, RadioField, FloatField
+from wtforms import Form, BooleanField, SelectField, TextField, RadioField, IntegerField
 from wtforms.validators import DataRequired, Email, Optional
 from flask_admin.contrib.sqla.fields import QuerySelectMultipleField, QuerySelectField
 from flask_admin.helpers import get_form_data
@@ -37,7 +37,7 @@ from advlabdb.utils import (
 
 
 class UserView(SecureModelView):
-    column_list = ["email", "active", "roles", "assistant"]
+    column_list = ["email", "active", "roles", "assistant", "active_semester"]
     column_searchable_list = ["email"]
     column_filters = ["active"]
     form_columns = ["email", "active", "roles"]
@@ -68,7 +68,7 @@ class UserView(SecureModelView):
             self.on_model_change(form, model, True)
             self.session.commit()
         except Exception as ex:
-            flash(ex, "error")
+            flash(str(ex), "error")
 
             self.session.rollback()
         else:
@@ -106,9 +106,10 @@ class RoleView(SecureModelView):
 class SemesterView(SecureModelView):
     can_edit = False
     can_delete = False
-    column_display_actions = False
+    can_view_details = True
 
     column_list = ["label", "parts"]
+    column_details_list = column_list + ["active_users"]
     form_columns = ["semester_label", "year", "transfer_parts", "transfer_assistants"]
 
     semesterLabels = ["WS", "SS"]
@@ -137,7 +138,7 @@ class SemesterView(SecureModelView):
             self.on_model_change(form, model, True)
             self.session.commit()
         except Exception as ex:
-            flash(ex, "error")
+            flash(str(ex), "error")
 
             self.session.rollback()
         else:
@@ -177,7 +178,7 @@ class SemesterView(SecureModelView):
 
             self.session.commit()
         except Exception as ex:
-            flash(ex, "error")
+            flash(str(ex), "error")
 
             self.session.rollback()
 
@@ -248,7 +249,7 @@ class PartStudentView(SecureModelView):
     class EditForm(CreateForm):
         student = None
         part = None
-        final_part_mark = FloatField("Final Part Mark", validators=[Optional()])
+        final_part_mark = IntegerField("Final Part Mark", validators=[Optional()])
 
     form = EditForm
 
@@ -316,7 +317,7 @@ class GroupView(SecureModelView):
             self.on_model_change(form, model, True)
             self.session.commit()
         except Exception as ex:
-            flash(ex, "error")
+            flash(str(ex), "error")
 
             self.session.rollback()
         else:
@@ -481,7 +482,7 @@ class GroupExperimentView(SecureModelView):
             self.on_model_change(form, model, True)
             self.session.commit()
         except Exception as ex:
-            flash(ex, "error")
+            flash(str(ex), "error")
 
             self.session.rollback()
         else:
diff --git a/advlabdb/models.py b/advlabdb/models.py
index f5e78c3..f141ff0 100644
--- a/advlabdb/models.py
+++ b/advlabdb/models.py
@@ -17,7 +17,7 @@ from advlabdb.configUtils import getConfig
 
 class Student(db.Model):
     id = db.Column(db.Integer, primary_key=True)
-    student_number = db.Column(db.Integer, nullable=False, unique=True)
+    student_number = db.Column(db.Integer, db.CheckConstraint("student_number > -1"), nullable=False, unique=True)
     first_name = db.Column(db.String(100), nullable=False)
     last_name = db.Column(db.String(100), nullable=False)
     uni_email = db.Column(db.String(200), nullable=False, unique=True)
@@ -37,7 +37,12 @@ class Student(db.Model):
 class PartStudent(db.Model):
     # A student doing a specific part
     id = db.Column(db.Integer, primary_key=True)
-    final_part_mark = db.Column(db.Integer, nullable=True)
+    final_part_mark = db.Column(
+        db.Integer,
+        db.CheckConstraint("final_part_mark > -1"),
+        db.CheckConstraint("final_part_mark < 16"),
+        nullable=True,
+    )
     student_id = db.Column(db.Integer, db.ForeignKey("student.id"), nullable=False)
     part_id = db.Column(db.Integer, db.ForeignKey("part.id"), nullable=False)
     group_id = db.Column(db.Integer, db.ForeignKey("group.id"), nullable=True)
@@ -57,7 +62,7 @@ class PartStudent(db.Model):
 
 class Group(db.Model):
     id = db.Column(db.Integer, primary_key=True)
-    number = db.Column(db.Integer, nullable=False)
+    number = db.Column(db.Integer, db.CheckConstraint("number > 0"), nullable=False)
     part_id = db.Column(db.Integer, db.ForeignKey("part.id"), nullable=False)
     part_students = db.relationship("PartStudent", backref="group", lazy=True)
     group_experiments = db.relationship("GroupExperiment", backref="group", lazy=True)
@@ -109,7 +114,7 @@ class Experiment(db.Model):
     room = db.Column(db.String(100), nullable=False)
     building = db.Column(db.String(100), nullable=False)
     responsibility = db.Column(db.String(200), nullable=True)
-    duration_in_days = db.Column(db.Integer, nullable=False)
+    duration_in_days = db.Column(db.Integer, db.CheckConstraint("duration_in_days > -1"), nullable=False)
     active = db.Column(db.Boolean, nullable=False, default=True)
     oral_weighting = db.Column(db.Float, nullable=False)
     protocol_weighting = db.Column(db.Float, nullable=False)
@@ -204,6 +209,7 @@ class Semester(db.Model):
     label = db.Column(db.String(100), nullable=False, unique=True)  # WS2122 for example
     parts = db.relationship("Part", backref="semester", lazy=True)
     semester_experiments = db.relationship("SemesterExperiment", backref="semester", lazy=True)
+    active_users = db.relationship("User", backref="active_semester", lazy=True)
 
     def repr(self):
         return f"{self.label}"
@@ -224,8 +230,12 @@ class Semester(db.Model):
 class ExperimentMark(db.Model):
     # A mark for a student after a specific experiment
     id = db.Column(db.Integer, primary_key=True)
-    oral_mark = db.Column(db.Integer, nullable=True)
-    protocol_mark = db.Column(db.Integer, nullable=True)
+    oral_mark = db.Column(
+        db.Integer, db.CheckConstraint("oral_mark > -1"), db.CheckConstraint("oral_mark < 16"), nullable=True
+    )
+    protocol_mark = db.Column(
+        db.Integer, db.CheckConstraint("protocol_mark > -1"), db.CheckConstraint("protocol_mark < 16"), nullable=True
+    )
     part_student_id = db.Column(db.Integer, db.ForeignKey("part_student.id"), nullable=False)
     group_experiment_id = db.Column(db.Integer, db.ForeignKey("group_experiment.id"), nullable=False)
     assistant_id = db.Column(
@@ -243,7 +253,7 @@ class ExperimentMark(db.Model):
 
 class User(db.Model, FsUserMixin):
     assistant = db.relationship("Assistant", backref="user", lazy=True, uselist=False)
-    active_semester_id = db.Column(db.Integer, nullable=True)
+    active_semester_id = db.Column(db.Integer, db.ForeignKey("semester.id"), nullable=True)
 
     def repr(self):
         return f"{self.email}"