добавила реализацию специализации

BeautySalon/BeautySalonDBModels/Implements/SpecialisationDB.cs

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+using BeautySalonDBModels.Models;
+using Npgsql;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace BeautySalonDBModels.Implements
+{
+    public class SpecialisationDB : AbstractWorkWithStorage<Specialisation>
+    {
+        public override void Add(Specialisation specialisation)
+        {
+            using var conn = GetConnection();
+            conn.Open();
+            using var cmd = new NpgsqlCommand("INSERT INTO specialisations (specialisation_name) " +
+                "VALUES (@Name)", conn);
+            cmd.Parameters.AddWithValue("@Name", specialisation.Name);
+            cmd.ExecuteNonQuery();
+        }
+
+        public override Specialisation? GetObject(int id)
+        {
+            using var conn = GetConnection();
+            conn.Open();
+            using var cmd = new NpgsqlCommand("SELECT * FROM specialisations WHERE specialisation_id = {id}", conn);
+            using var reader = cmd.ExecuteReader();
+            if (reader.Read())
+            {
+                return new Specialisation
+                {
+                    SpecialisationId = reader.GetInt32(0),
+                    Name = reader.GetString(1)
+                };
+            }
+            return null;
+        }
+
+        public override List<Specialisation> GetObjects()
+        {
+            var specialisations = new List<Specialisation>();
+            using var conn = GetConnection();
+            conn.Open();
+            using var cmd = new NpgsqlCommand("SELECT * FROM specialisations order by specialisation_id", conn);
+            using var reader = cmd.ExecuteReader();
+            while (reader.Read())
+            {
+                specialisations.Add(new Specialisation
+                {
+                    SpecialisationId = reader.GetInt32(0),
+                    Name = reader.GetString(1)
+                });
+            }
+            return specialisations;
+        }
+
+        public override Specialisation? Remove(int id)
+        {
+            var specialisation = GetObject(id);
+            using var conn = GetConnection();
+            conn.Open();
+            using var cmd = new NpgsqlCommand("delete from specialisations where specialisation_id = {id}", conn);
+            cmd.ExecuteNonQuery();
+            return specialisation;
+        }
+
+        public override void Update(Specialisation specialisation)
+        {
+            using var conn = GetConnection();
+            conn.Open();
+            using var cmd = new NpgsqlCommand("update specialisation set specialisation_name = {specialisation.Name}, " +
+                "where specialisation_id = {specialisation.SpecialisationId}", conn);
+            cmd.ExecuteNonQuery();
+        }
+    }
+}