diff --git a/advlabdb/models.py b/advlabdb/models.py
index dd93f3d..f5e78c3 100644
--- a/advlabdb/models.py
+++ b/advlabdb/models.py
@@ -37,12 +37,17 @@ 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.Float, nullable=True)
+    final_part_mark = db.Column(db.Integer, 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)
     experiment_marks = db.relationship("ExperimentMark", backref="part_student", lazy=True)
 
+    __table_args__ = (
+        db.UniqueConstraint(student_id, part_id),
+        db.UniqueConstraint(student_id, group_id),
+    )
+
     def repr(self):
         return f"{self.student.repr()} {self.part.repr()}"
 
@@ -57,6 +62,8 @@ class Group(db.Model):
     part_students = db.relationship("PartStudent", backref="group", lazy=True)
     group_experiments = db.relationship("GroupExperiment", backref="group", lazy=True)
 
+    __table_args__ = (db.UniqueConstraint(number, part_id),)
+
     def repr(self):
         return f"{self.number} {self.part.repr()}"
 
@@ -72,6 +79,8 @@ class GroupExperiment(db.Model):
     appointments = db.relationship("Appointment", backref="group_experiment", lazy=True)
     experiment_marks = db.relationship("ExperimentMark", backref="group_experiment", lazy=True)
 
+    __table_args__ = (db.UniqueConstraint(semester_experiment_id, group_id),)
+
     def repr(self):
         return f"SemExp {self.semester_experiment.repr()}; Gr {self.group.repr()}"
 
@@ -83,17 +92,11 @@ class GroupExperiment(db.Model):
             student = partStudent.student
             for partStudent in student.part_students:
                 for experimentMark in partStudent.experiment_marks:
-                    if (
-                        experimentMark.group_experiment.semester_experiment.experiment == semester_experiment.experiment
-                    ):  # TODO Check if passed
+                    if experimentMark.group_experiment.semester_experiment.experiment == semester_experiment.experiment:
                         raise Exception(
-                            f"{student} has already done {semester_experiment.experiment} in {partStudent.part}!"
+                            f"{student} has already done {semester_experiment.experiment} in {partStudent.part} and had {experimentMark}!"
                         )
 
-        for groupExperiment in group.group_experiments:
-            if groupExperiment.semester_experiment == semester_experiment:  # TODO: What if did not pass?
-                raise Exception(f"{group} already has {semester_experiment}!")
-
         return GroupExperiment(semester_experiment=semester_experiment, group=group)
 
 
@@ -129,7 +132,7 @@ experiment_assistant = db.Table(
 
 
 class SemesterExperiment(db.Model):
-    # An experiment in a specific part
+    # An experiment in a specific semester
     id = db.Column(db.Integer, primary_key=True)
     experiment_id = db.Column(db.Integer, db.ForeignKey("experiment.id"), nullable=False)
     semester_id = db.Column(db.Integer, db.ForeignKey("semester.id"), nullable=False)
@@ -138,6 +141,8 @@ class SemesterExperiment(db.Model):
     )
     group_experiments = db.relationship("GroupExperiment", backref="semester_experiment", lazy=True)
 
+    __table_args__ = (db.UniqueConstraint(experiment_id, semester_id),)
+
     def repr(self):
         return f"{self.experiment.repr()} {self.semester.repr()}"
 
@@ -153,7 +158,7 @@ class Assistant(db.Model):
     mobile_phone_number = db.Column(db.String(50), nullable=True)
     room = db.Column(db.String(100), nullable=True)
     building = db.Column(db.String(100), nullable=True)
-    user_id = db.Column(db.Integer, db.ForeignKey("user.id"), nullable=False)
+    user_id = db.Column(db.Integer, db.ForeignKey("user.id"), nullable=False, unique=True)
     appointments = db.relationship("Appointment", backref="assistant", lazy=True)
     experiment_marks = db.relationship("ExperimentMark", backref="assistant", lazy=True)
 
@@ -185,6 +190,8 @@ class Part(db.Model):
     part_students = db.relationship("PartStudent", backref="part", lazy=True)
     groups = db.relationship("Group", backref="part", lazy=True)
 
+    __table_args__ = (db.UniqueConstraint(label, semester_id),)
+
     def repr(self):
         return f"{self.label} {self.semester.repr()}"
 
@@ -217,14 +224,16 @@ 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.Float, nullable=True)
-    protocol_mark = db.Column(db.Float, nullable=True)
+    oral_mark = db.Column(db.Integer, nullable=True)
+    protocol_mark = db.Column(db.Integer, 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(
         db.Integer, db.ForeignKey("assistant.id"), nullable=True
     )  # The assistant who gave the mark
 
+    __table_args__ = (db.UniqueConstraint(part_student_id, group_experiment_id),)
+
     def repr(self):
         return f"Oral {round(self.oral_mark, 1)}; Prot {round(self.protocol_mark, 1)}"