diff --git a/backend/app/base/utils.py b/backend/app/base/utils.py
index 91e6feb..2085510 100644
--- a/backend/app/base/utils.py
+++ b/backend/app/base/utils.py
@@ -1,6 +1,6 @@
 from typing import TypedDict, Tuple
 
-from flask import current_app
+from flask import current_app, abort
 from flask_sqlalchemy import BaseQuery
 from sqlalchemy import desc
 
@@ -20,14 +20,9 @@ def order_by_column_name(query: BaseQuery, model_field: str, order_by_col_name:
     return query
 
 
-def paginate_models(page: str, query: BaseQuery, per_page = 10) -> PaginationResponse or Tuple[dict, int]:
+def paginate_models(page: int, query: BaseQuery, per_page=10) -> PaginationResponse:
     default_page = 1
-
     if page is not None:
-        try:
-            page = int(page)
-        except ValueError:
-            return {"error": f"Invalid page! Page must be integer!"}, 400
         query = query.paginate(page=page, per_page=per_page, error_out=False)
     else:
         query = query.paginate(page=default_page, per_page=per_page, error_out=False)
diff --git a/backend/app/coordinator/routes/__init__.py b/backend/app/coordinator/routes/__init__.py
index 6da1701..433899d 100644
--- a/backend/app/coordinator/routes/__init__.py
+++ b/backend/app/coordinator/routes/__init__.py
@@ -3,9 +3,11 @@ from flask import Blueprint
 from .students import bp as students_bp
 from .project_supervisor import bp as project_supervisor_bp
 from .groups import bp as groups_bp
+from .project_supervisor import bp as project_supervisor_bp
 
 bp = Blueprint("coordinator", __name__, url_prefix="/coordinator")
 
 bp.register_blueprint(students_bp)
 bp.register_blueprint(project_supervisor_bp)
 bp.register_blueprint(groups_bp)
+bp.register_blueprint(project_supervisor_bp)
diff --git a/backend/app/coordinator/routes/groups.py b/backend/app/coordinator/routes/groups.py
index 54a768d..393ff3f 100644
--- a/backend/app/coordinator/routes/groups.py
+++ b/backend/app/coordinator/routes/groups.py
@@ -5,8 +5,8 @@ from flask_sqlalchemy import get_debug_queries
 from ...students.models import Group, Student
 from ...project_supervisor.models import ProjectSupervisor
 from ..schemas import GroupSchema, GroupEditSchema, GroupsPaginationSchema, \
-    GroupCreateSchema, MessageSchema, FileSchema, GroupQuerySchema
-from ...dependencies import db, ma
+    GroupCreateSchema, MessageSchema, GroupQuerySchema
+from ...dependencies import db
 from ...base.utils import paginate_models
 
 bp = APIBlueprint("groups", __name__, url_prefix="/groups")
@@ -19,15 +19,14 @@ def list_groups(query: dict) -> dict:
     search_name = query.get('name')
     page = query.get('page')
     per_page = query.get('per_page')
-    
+
     groups_query = Group.search_by_name(search_name)
 
-    response = paginate_models(page, groups_query, per_page)
-    if (message := response.get('message')) is not None:
-        abort(response['status_code'], message)
+    data = paginate_models(page, groups_query, per_page)
+
     return {
-        "groups": response['items'],
-        "max_pages": response['max_pages']
+        "groups": data['items'],
+        "max_pages": data['max_pages']
     }
 
 
@@ -36,29 +35,36 @@ def list_groups(query: dict) -> dict:
 @bp.output(MessageSchema)
 def create_group(data: dict) -> dict:
     name = data['name']
-    students = data['students']
+    students_indexes = data['students']
     project_supervisor_id = data['project_supervisor_id']
-    group = Group.query.filter_by(name=name).first()
-    if group is not None:
-        abort(400, "Group has already exists!")
-    
-    project_supervisor = ProjectSupervisor.query.filter_by(id=project_supervisor_id).first()
 
-    if project_supervisor is None:
-        abort(404, f"Student with id {project_supervisor_id} doesn't exist!")
-    
-    group = Group(name=name, project_supervisor_id = data['project_supervisor_id'])
+    # can assign a new group to project_supervisor
+    result = db.session.query(ProjectSupervisor.count_groups - db.func.count(ProjectSupervisor.id)). \
+        join(Group).filter(ProjectSupervisor.id == project_supervisor_id). \
+        group_by(ProjectSupervisor.id).scalar()
 
+    if result is None:
+        abort(400, "Project Supervisor doesnt exist")
+    elif result <= 0:
+        abort(400, "Can't create new group, project supervisor achieved a limit of groups")
+
+    group = Group(name=name, project_supervisor_id=project_supervisor_id)
+
+    students_without_groups = db.session.query(Student).join(Group, isouter=True) \
+        .filter(Group.id.is_(None)).filter(Student.index.in_(students_indexes)).count()
+
+    if students_without_groups != len(students_indexes):
+        abort(400, "One or more students have already belonged to group!")
+
+    students = db.session.query(Student).filter(Student.index.in_(students_indexes)).all()
     for student in students:
-        st = Student.query(index = student.index).first()
-        if st is None:
-            abort(404, 'Not found student!')
-        st.group_id = group.id
-    
+        student.group_id = group.id
+
+    db.session.add_all(students)
     db.session.add(group)
     db.session.commit()
 
-    return {"message": "Student was created!"}
+    return {"message": "Project Supervisor was created!"}
 
 
 @bp.route("/<int:id>/", methods=["GET"])
@@ -87,13 +93,13 @@ def delete_group(id: int) -> dict:
 def edit_group(id: int, data: dict) -> dict:
     if not data:
         abort(400, 'You have passed empty data!')
-    
+
     group_query = Group.query.filter_by(id=id)
     group = group_query.first()
 
     if group is None:
         abort(400, f"Group with id {id} doesn't exist!")
-    
-    group_query.update(group)
+
+    group_query.update(data)
     db.session.commit()
     return {"message": "Group was updated!"}
diff --git a/backend/app/coordinator/routes/project_supervisor.py b/backend/app/coordinator/routes/project_supervisor.py
index c8bd0a2..ddeeda7 100644
--- a/backend/app/coordinator/routes/project_supervisor.py
+++ b/backend/app/coordinator/routes/project_supervisor.py
@@ -3,9 +3,10 @@ from apiflask import APIBlueprint
 from flask_sqlalchemy import get_debug_queries
 
 from ...project_supervisor.models import ProjectSupervisor
+from ...students.models import Group
 from ..schemas import ProjectSupervisorSchema, ProjectSupervisorEditSchema, ProjectSupervisorsPaginationSchema, \
-    ProjectSupervisorCreateSchema, MessageSchema, FileSchema, ProjectSupervisorQuerySchema
-from ...dependencies import db, ma
+    ProjectSupervisorCreateSchema, MessageSchema, ProjectSupervisorQuerySchema
+from ...dependencies import db
 from ...base.utils import paginate_models
 
 bp = APIBlueprint("project_supervisor", __name__, url_prefix="/project_supervisor")
@@ -25,13 +26,11 @@ def list_project_supervisors(query: dict) -> dict:
     project_supervisor_query = ProjectSupervisor.search_by_fullname_and_mode_and_order_by_first_name_or_last_name(
         fullname, mode, order_by_first_name, order_by_last_name)
 
-    response = paginate_models(page, project_supervisor_query, per_page)
-    if (message := response.get('message')) is not None:
-        abort(response['status_code'], message)
+    data = paginate_models(page, project_supervisor_query, per_page)
     # print(get_debug_queries()[0])
     return {
-        "project_supervisors": response['items'],
-        "max_pages": response['max_pages']
+        "project_supervisors": data['items'],
+        "max_pages": data['max_pages']
     }
 
 
@@ -41,18 +40,11 @@ def list_project_supervisors(query: dict) -> dict:
 def create_project_supervisor(data: dict) -> dict:
     first_name = data['first_name']
     last_name = data['last_name']
-    email = data['email']
-    limit_group = data['limit_group']
-    mode = data['mode']
     project_supervisor = ProjectSupervisor.query.filter_by(first_name=first_name).filter_by(last_name=last_name).first()
     if project_supervisor is not None:
         abort(400, "Project Supervisor has already exists!")
     
-    project_supervisor = ProjectSupervisor(first_name=first_name, 
-                            last_name = last_name,
-                            email = email,
-                            limit_group = limit_group,
-                            mode = mode)
+    project_supervisor = ProjectSupervisor(**data)
 
     db.session.add(project_supervisor)
     db.session.commit()
@@ -75,8 +67,10 @@ def delete_project_supervisor(id: int) -> dict:
     project_supervisor = ProjectSupervisor.query.filter_by(id=id).first()
     if project_supervisor is None:
         abort(400, f"Project Supervisor with id {id} doesn't exist!")
-    
-    if project_supervisor.count_groups > 0:
+
+    count_groups = db.session.query(db.func.count(ProjectSupervisor.id)).join(Group).\
+        filter(ProjectSupervisor.id == id).group_by(ProjectSupervisor.id).scalar()
+    if count_groups > 0:
         abort(400, f"Project Supervisor with id {id} has gropus!")
 
     db.session.delete(project_supervisor)
@@ -97,6 +91,6 @@ def edit_project_supervisor(id: int, data: dict) -> dict:
     if project_supervisor is None:
         abort(400, f"Project Supervisor with id {id} doesn't exist!")
     
-    project_supervisor_query.update(project_supervisor)
+    project_supervisor_query.update(data)
     db.session.commit()
     return {"message": "Project Supervisor was updated!"}
diff --git a/backend/app/coordinator/routes/students.py b/backend/app/coordinator/routes/students.py
index 74c19fc..7546445 100644
--- a/backend/app/coordinator/routes/students.py
+++ b/backend/app/coordinator/routes/students.py
@@ -33,13 +33,11 @@ def list_students(query: dict) -> dict:
     student_query = Student.search_by_fullname_and_mode_and_order_by_first_name_or_last_name(
         fullname, mode, order_by_first_name, order_by_last_name)
 
-    response = paginate_models(page, student_query, per_page)
-    if (message := response.get('message')) is not None:
-        abort(response['status_code'], message)
+    data = paginate_models(page, student_query, per_page)
     # print(get_debug_queries()[0])
     return {
-        "students": response['items'],
-        "max_pages": response['max_pages']
+        "students": data['items'],
+        "max_pages": data['max_pages']
     }
 
 
diff --git a/backend/app/coordinator/schemas.py b/backend/app/coordinator/schemas.py
index 419cbc9..c507625 100644
--- a/backend/app/coordinator/schemas.py
+++ b/backend/app/coordinator/schemas.py
@@ -3,6 +3,7 @@ from ..students.models import Student, Group
 from ..project_supervisor.models import ProjectSupervisor
 from marshmallow import fields, validate, ValidationError
 
+
 def validate_index(index):
     if len(str(index)) > 6:
         raise ValidationError("Length of index is too long!")
@@ -18,7 +19,7 @@ class ProjectSupervisorSchema(ma.SQLAlchemyAutoSchema):
 
 class GroupSchema(ma.SQLAlchemyAutoSchema):
     project_supervisor = fields.Nested(ProjectSupervisorSchema)
-    
+
     class Meta:
         model = Group
 
@@ -81,8 +82,8 @@ class GroupsPaginationSchema(ma.Schema):
 
 class GroupCreateSchema(ma.Schema):
     name = fields.Str(validate=validate.Length(min=1, max=255), required=True)
-    project_supervisor_id = fields.Integer(validate=validate_index, required=True)
-    students = fields.List(fields.Nested(StudentSchema), validate=validate.Length(min=1, max=255), required=True)
+    project_supervisor_id = fields.Integer(required=True)
+    students = fields.List(fields.Integer(validate=validate_index, required=True))
 
 
 class GroupEditSchema(ma.Schema):
diff --git a/backend/app/project_supervisor/models.py b/backend/app/project_supervisor/models.py
index 6d296a6..5f0bd6b 100644
--- a/backend/app/project_supervisor/models.py
+++ b/backend/app/project_supervisor/models.py
@@ -6,6 +6,7 @@ from sqlalchemy import or_
 from sqlalchemy.sql import text
 from ..base.utils import order_by_column_name
 
+
 class ProjectSupervisor(Base, Person):
     __tablename__ = "project_supervisors"
 
@@ -21,16 +22,15 @@ class ProjectSupervisor(Base, Person):
         project_supervisors_query = cls.query
 
         if mode is not None:
-            project_supervisors_query = project_supervisors_query.filter(mode != 1-mode)
+            project_supervisors_query = project_supervisors_query.filter(mode != 1 - mode)
 
         if fullname is not None:
-            """This works only for sqlite3 database - concat function  doesn't exist so i used builtin concat 
-            operator specific only for sqlite db - || """
             project_supervisors_query = project_supervisors_query.filter(
-                text("project_supervisorss_first_name || ' ' || project_supervisorss_last_name LIKE :fullname ")
-            ).params(fullname=f'{fullname}%')
+                (ProjectSupervisor.first_name + ' ' + ProjectSupervisor.last_name).like(f'{fullname}%'))
 
-        project_supervisors_query = order_by_column_name(project_supervisors_query, ProjectSupervisor.first_name, order_by_first_name)
-        project_supervisors_query = order_by_column_name(project_supervisors_query, ProjectSupervisor.last_name, order_by_last_name)
+        project_supervisors_query = order_by_column_name(project_supervisors_query, ProjectSupervisor.first_name,
+                                                         order_by_first_name)
+        project_supervisors_query = order_by_column_name(project_supervisors_query, ProjectSupervisor.last_name,
+                                                         order_by_last_name)
 
         return project_supervisors_query
diff --git a/backend/app/students/models.py b/backend/app/students/models.py
index d41dd3d..4bfeef3 100644
--- a/backend/app/students/models.py
+++ b/backend/app/students/models.py
@@ -23,15 +23,11 @@ class Group(Base):
         group_query = cls.query
 
         if search_name is not None:
-            group_query = group_query.filter(
-                text("groups_name LIKE :search_name ")
-            ).params(search_name=f'{search_name}%')
-        
+            group_query = group_query.filter(Group.name.like(f'{search_name}%'))
+
         return group_query
 
 
-
-
 class Student(Person):
     __tablename__ = "students"
 
@@ -52,11 +48,7 @@ class Student(Person):
             student_query = student_query.filter_by(mode=mode)
 
         if fullname is not None:
-            """This works only for sqlite3 database - concat function  doesn't exist so i used builtin concat 
-            operator specific only for sqlite db - || """
-            student_query = student_query.filter(
-                text("students_first_name || ' ' || students_last_name LIKE :fullname ")
-            ).params(fullname=f'{fullname}%')
+            student_query = student_query.filter((Student.first_name + ' ' + Student.last_name).like(f'{fullname}%'))
 
         student_query = order_by_column_name(student_query, Student.first_name, order_by_first_name)
         student_query = order_by_column_name(student_query, Student.last_name, order_by_last_name)
diff --git a/backend/app/students/routes/registrations.py b/backend/app/students/routes/registrations.py
index 5ee0a39..84cd123 100644
--- a/backend/app/students/routes/registrations.py
+++ b/backend/app/students/routes/registrations.py
@@ -24,16 +24,14 @@ def list_available_groups(query: dict) -> dict:
         ps_query = ps_query.filter(ProjectSupervisor.mode == mode)
     ps_query = ps_query.group_by(Group.id)
 
-    response = paginate_models(page, ps_query, per_page)
-    if (message := response.get('message')) is not None:
-        abort(response['status_code'], message)
+    data = paginate_models(page, ps_query, per_page)
 
     project_supervisors = []
-    for project_supervisor, available_groups in response['items']:
+    for project_supervisor, available_groups in data['items']:
         setattr(project_supervisor, 'available_groups', available_groups)
         project_supervisors.append(project_supervisor)
 
     return {
         "project_supervisors": project_supervisors,
-        "max_pages": response['max_pages']
+        "max_pages": data['max_pages']
     }