implemented basic crud logic; NB: CONNECTION STRING IN PROGRAM.CS IS EMPTY

Backend.Api/Data/DataContext.cs

@@ -0,0 +1,14 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace Backend.Api.Data
+{
+    public class DataContext : DbContext
+    {
+        public DataContext(DbContextOptions<DataContext> options) : base(options)
+        {
+
+        }
+        public DbSet<User> Users { get; set; }
+        public DbSet<Vehicle> Vehicles { get; set; }
+    }
+}

Backend.Api/Data/Services/UserService.cs

@@ -0,0 +1,47 @@
+namespace Backend.Api.Data.Services
+{
+    public class UserService
+    {
+        private readonly DataContext _context;
+        public UserService(DataContext context)
+        {
+            _context = context;
+        }
+
+        public void Add(User user)
+        {
+            _context.Users.Add(user);
+            _context.SaveChanges();
+        }
+        
+        public void Remove(long id)
+        {
+            var user = _context.Users.FirstOrDefault(x => x.Id == id);
+            if (user != null)
+            {
+                _context.Users.Remove(user);
+                _context.SaveChanges();
+            }
+        }
+
+        public void Update(long id, User newUser)
+        {
+            var oldUser = _context.Users.FirstOrDefault(x =>x.Id == id);
+            oldUser = newUser;
+            _context.SaveChanges();
+        }
+
+        public User? Get(long id)
+        {
+            var user = _context.Users.FirstOrDefault(x => x.Id == id);
+            return user;
+        }
+
+        public List<Vehicle> GetVehicles(long id)
+        {
+            var userId = _context.Users.FirstOrDefault(x => x.Id == id).Id;
+            var vehicles = _context.Vehicles.Where(x => x.OwnerId == userId).ToList<Vehicle>();
+            return vehicles;
+        }
+    }
+}

Backend.Api/Data/Services/VehicleService.cs

@@ -0,0 +1,45 @@
+namespace Backend.Api.Data.Services
+{
+    public class VehicleService
+    {
+        private readonly DataContext _context;
+        public VehicleService(DataContext context)
+        {
+            _context = context;
+        }
+
+        public void Add(Vehicle vehicle)
+        {
+            _context.Vehicles.Add(vehicle);
+            _context.SaveChanges();
+        }
+
+        public void Remove(long id)
+        {
+            var vehicle = _context.Vehicles.FirstOrDefault(x => x.Id == id);
+            if (vehicle != null)
+            {
+                _context.Vehicles.Remove(vehicle);
+                _context.SaveChanges();
+            }
+        }
+        
+        public void Update(long id, Vehicle newVehicle)
+        {
+            var oldVehicle = _context.Vehicles.FirstOrDefault(x => x.Id == id);
+            oldVehicle = newVehicle;
+            _context.SaveChanges();
+        }
+
+        public Vehicle? Get(long id)
+        {
+            var vehicle = _context.Vehicles.FirstOrDefault(x => x.Id == id);
+            return vehicle;
+        }
+        public User? GetOwner(long id)
+        {
+            var ownerId = _context.Vehicles.FirstOrDefault(x => x.Id == id).OwnerId;
+            return _context.Users.FirstOrDefault(x => x.Id == ownerId);
+        }
+
+    }

Backend.Api/Data/User.cs

@@ -0,0 +1,9 @@
+namespace Backend.Api.Data
+{
+    public class User
+    {
+        public long Id { get; set; }
+        public string Name { get; set; } = "Undefined name";
+        public string Surname { get; set; } = "Undefined surname";
+    }
+}

Backend.Api/Data/Vehicle.cs

@@ -0,0 +1,9 @@
+namespace Backend.Api.Data
+{
+    public class Vehicle
+    {
+        public long Id { get; set; }
+        public long OwnerId { get; set; }
+        public string PlateNumber { get; set; } = "Undefined plate number";
+    }
+}