добавила сеты и почти реализовала хранилище клиента

BeautySalon/BeautySalonDBModels/AbstractWorkWithStorage.cs

@@ -1,13 +1,19 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
+using BeautySalonDBModels.Models;
+using Npgsql;
 
 namespace BeautySalonDBModels
 {
-    public abstract class AbstractWorkWithStorage
+    public abstract class AbstractWorkWithStorage<T>
     {
-        public abstract void AddClient(Clien);
+        public abstract void Add(T obj);
+        public abstract T? Remove(int id);
+        public abstract void Update(T obj);
+        public abstract List<T> GetObjects();
+        public abstract T? GetObject(int id);
+
+        public NpgsqlConnection GetConnection()
+        {
+            return new NpgsqlConnection("Host=localhost;Port=5555;Username=elina;Database=beauty_salon;Password=elina");
+        }
     }
 }

BeautySalon/BeautySalonDBModels/Implements/ClientDB.cs

@@ -0,0 +1,69 @@
+using BeautySalonDBModels.Models;
+using Npgsql;
+
+namespace BeautySalonDBModels.Implements
+{
+    public class ClientDB : AbstractWorkWithStorage<Client>
+    {
+        public override void Add(Client client)
+        {
+            using var conn = GetConnection();
+            conn.Open();
+            using var cmd = new NpgsqlCommand("INSERT INTO clients (fio, age) VALUES (@FIO, @Age)", conn);
+            cmd.Parameters.AddWithValue("@FIO", client.FIO);
+            cmd.Parameters.AddWithValue("@Age", client.Age);
+            cmd.ExecuteNonQuery();
+        }
+
+        public override Client? GetObject(int id)
+        {
+            using var conn = GetConnection();
+            conn.Open();
+            using var cmd = new NpgsqlCommand("SELECT * FROM clients WHERE client_id = {id}", conn);
+            using var reader = cmd.ExecuteReader();
+            if (reader.Read())
+            {
+                return new Client
+                {
+                    ClientId = reader.GetInt32(0),
+                    FIO = reader.GetString(1),
+                    Age = reader.GetInt32(2)
+                };
+            }
+            return null;
+        }
+
+        public override List<Client> GetObjects()
+        {
+            var clients = new List<Client>();
+            using var conn = GetConnection();
+            conn.Open();
+            using var cmd = new NpgsqlCommand("SELECT * FROM clients order by id", conn);
+            using var reader = cmd.ExecuteReader();
+            while (reader.Read())
+            {
+                clients.Add(new Client
+                {
+                    ClientId = reader.GetInt32(0),
+                    FIO = reader.GetString(1),
+                    Age = reader.GetInt32(2)
+                });
+            }
+            return clients;
+        }
+
+        public override Client? Remove(int id)
+        {
+            var client = GetObject(id);
+            using var conn = GetConnection();
+            conn.Open();
+            using var cmd = new NpgsqlCommand("delete from clients where client_id = {id}", conn);
+            return client;
+        }
+
+        public override void Update(Client client)
+        {
+
+        }
+    }
+}

BeautySalon/BeautySalonDBModels/Models/Cheque.cs

@@ -2,8 +2,8 @@
 {
     public class Cheque
     {
-        public int ChequeId { get; }
-        public int ClientId { get; }
-        public int ReceptionId { get; }
+        public int ChequeId { get; set; }
+        public int ClientId { get; set; }
+        public int ReceptionId { get; set; }
     }
 }

BeautySalon/BeautySalonDBModels/Models/Client.cs

@@ -2,8 +2,8 @@
 {
     public class Client
     {
-        public int ClientId { get; }
-        public string FIO { get; } = string.Empty;
-        public int Age { get; }
+        public int ClientId { get; set; }
+        public string FIO { get; set; } = string.Empty;
+        public int Age { get; set; }
     }
 }

BeautySalon/BeautySalonDBModels/Models/Master.cs

@@ -2,8 +2,8 @@
 {
     public class Master
     {
-        public int MasterId { get; }
-        public int SpecialisationId { get; }
-        public string FIO { get; } = string.Empty;
+        public int MasterId { get; set; }
+        public int SpecialisationId { get; set; }
+        public string FIO { get; set; } = string.Empty;
     }
 }

BeautySalon/BeautySalonDBModels/Models/Reception.cs

@@ -2,9 +2,9 @@
 {
     public class Reception
     {
-        public int ReceptionId { get; }
-        public int MasterId { get; }
-        public int ServiceId { get; }
-        public DateTime DateReception { get; }
+        public int ReceptionId { get; set; }
+        public int MasterId { get; set; }
+        public int ServiceId { get; set; }
+        public DateTime DateReception { get; set; }
     }
 }

BeautySalon/BeautySalonDBModels/Models/Service.cs

@@ -2,9 +2,9 @@
 {
     public class Service
     {
-        public int ServiceId { get; }
-        public string ServiceName { get; } = string.Empty;
-        public double Price { get; }
-        public int SpecialisationId { get; }
+        public int ServiceId { get; set; }
+        public string ServiceName { get; set; } = string.Empty;
+        public double Price { get; set; }
+        public int SpecialisationId { get; set; }
     }
 }

BeautySalon/BeautySalonDBModels/Models/Specialisation.cs

@@ -2,7 +2,7 @@
 {
     public class Specialisation
     {
-        public int SpecialisationId { get; }
-        public string Name { get; } = string.Empty; 
+        public int SpecialisationId { get; set; }
+        public string Name { get; set; } = string.Empty; 
     }
 }