Все поудалял, начинаем по новой

Medical/Medical.sln

@@ -3,11 +3,7 @@ Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
 VisualStudioVersion = 17.9.34714.143
 MinimumVisualStudioVersion = 10.0.40219.1
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MedicalView", "MedicalView\MedicalView.csproj", "{9CEA3FF8-036C-4844-9376-8B09E8507E7F}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MedicalView", "MedicalView\MedicalView.csproj", "{9CEA3FF8-036C-4844-9376-8B09E8507E7F}"
-EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MedicalDatabaseContracts", "MedicalDatabaseContracts\MedicalDatabaseContracts.csproj", "{994E2E14-D535-4FDA-B380-8F0796CF3B40}"
-EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MedicalPostgresDatabase", "MedicalPostgresDatabase\MedicalPostgresDatabase.csproj", "{49D1A466-7D84-4333-B5EA-97D12606B986}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -19,14 +15,6 @@ Global
 		{9CEA3FF8-036C-4844-9376-8B09E8507E7F}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{9CEA3FF8-036C-4844-9376-8B09E8507E7F}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{9CEA3FF8-036C-4844-9376-8B09E8507E7F}.Release|Any CPU.Build.0 = Release|Any CPU
-		{994E2E14-D535-4FDA-B380-8F0796CF3B40}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{994E2E14-D535-4FDA-B380-8F0796CF3B40}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{994E2E14-D535-4FDA-B380-8F0796CF3B40}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{994E2E14-D535-4FDA-B380-8F0796CF3B40}.Release|Any CPU.Build.0 = Release|Any CPU
-		{49D1A466-7D84-4333-B5EA-97D12606B986}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{49D1A466-7D84-4333-B5EA-97D12606B986}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{49D1A466-7D84-4333-B5EA-97D12606B986}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{49D1A466-7D84-4333-B5EA-97D12606B986}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

Medical/MedicalDatabaseContracts/IModel.cs

@@ -0,0 +1,9 @@
+using Npgsql;
+
+namespace MedicalDatabaseContracts
+{
+    public interface IModel<T>
+    {
+        T CreateFromDataReader(NpgsqlDataReader reader);
+    }
+}

Medical/MedicalDatabaseContracts/MedicalDatabaseContracts.csproj

@@ -6,4 +6,8 @@
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="Npgsql" Version="8.0.2" />
+  </ItemGroup>
+
 </Project>

Medical/MedicalDatabaseContracts/Models/DiagnoseModel.cs

@@ -1,8 +1,19 @@
-namespace MedicalDatabaseContracts.Models
+using Npgsql;
+
+namespace MedicalDatabaseContracts.Models
 {
-    public class DiagnoseModel
+    public class DiagnoseModel : IModel<DiagnoseModel>
     {
         public long? DiagnoseId { get; set; }
         public string Name { get; set;} = string.Empty;
+
+        public static DiagnoseModel CreateFromDataReader(NpgsqlDataReader reader)
+        {
+            return new DiagnoseModel
+            {
+                DiagnoseId = Convert.ToInt32(reader["diagnose_id"]),
+                Name = Convert.ToString(reader["name"])
+            };
+        }
     }
 }

Medical/MedicalPostgresDatabase/DiagnosesStorage.cs

@@ -0,0 +1,42 @@
+using MedicalDatabaseContracts;
+using MedicalDatabaseContracts.Models;
+using Npgsql;
+
+namespace MedicalPostgresDatabase
+{
+    public class DiagnosesStorage : IStorage<DiagnoseModel>
+    {
+        private MedicalDatabaseSingleton _database;
+        public DiagnosesStorage()
+        {
+            _database = MedicalDatabaseSingleton.GetInstance();
+        }
+        public DiagnoseModel Create(DiagnoseModel entity)
+        {
+            throw new NotImplementedException();
+        }
+
+        public DiagnoseModel Delete(long id)
+        {
+            throw new NotImplementedException();
+        }
+
+        public DiagnoseModel Get(long id)
+        {
+            using var cmd = new NpgsqlCommand();
+            cmd.Connection = dbconnection;
+            cmd.CommandText = "";
+
+        }
+
+        public List<DiagnoseModel> GetAll()
+        {
+            throw new NotImplementedException();
+        }
+
+        public DiagnoseModel Update(long id, DiagnoseModel entity)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}

Medical/MedicalPostgresDatabase/MedicalDatabaseSingleton.cs

@@ -0,0 +1,47 @@
+using MedicalDatabaseContracts;
+using Npgsql;
+
+namespace MedicalPostgresDatabase
+{
+    public class MedicalDatabaseSingleton
+    {
+        private static MedicalDatabaseSingleton? instance;
+        private NpgsqlConnection _connection;
+        
+        public static MedicalDatabaseSingleton GetInstance()
+        {
+            if (instance == null)
+            {
+                instance = new MedicalDatabaseSingleton();
+            }
+            return instance;
+        }
+        private MedicalDatabaseSingleton()
+        {
+            _connection = new NpgsqlConnection(
+                connectionString: "Server=localhost;Port=5555;User Id=postgres;Password=postgres;Database=medicalbase;"
+            );
+            _connection.Open();
+            
+        }
+        public List<T> ExecuteQuerySelect<T>(string query) where T : IModel
+        {
+            using var command = new NpgsqlCommand();
+            command.Connection = _connection;
+            command.CommandText = query;
+            NpgsqlDataReader reader = command.ExecuteReader();
+            var list = new List<T>();
+            while (reader.Read())
+            {
+                list.Add(T.CreateFromDataReader());
+            }
+        }
+        public int ExecuteQuery(string query)
+        {
+            using var command = new NpgsqlCommand();
+            command.Connection = _connection;
+            command.CommandText = query;
+            return command.ExecuteNonQuery();
+        }
+    }
+}

Medical/MedicalPostgresDatabase/MedicalPostgresDatabase.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Npgsql" Version="8.0.2" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\MedicalDatabaseContracts\MedicalDatabaseContracts.csproj" />
+  </ItemGroup>
+
+</Project>

Medical/MedicalView/FormMain.Designer.cs

@@ -51,7 +51,7 @@
             menuStrip.Items.AddRange(new ToolStripItem[] { справочникиToolStripMenuItem, пациентыToolStripMenuItem1 });
             menuStrip.Location = new Point(0, 0);
             menuStrip.Name = "menuStrip";
-            menuStrip.Size = new Size(584, 24);
+            menuStrip.Size = new Size(755, 24);
             menuStrip.TabIndex = 0;
             menuStrip.Text = "menuStrip1";
             // 
@@ -94,7 +94,7 @@
             dataGridView.Name = "dataGridView";
             dataGridView.RowTemplate.Height = 25;
             dataGridView.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
-            dataGridView.Size = new Size(584, 277);
+            dataGridView.Size = new Size(755, 277);
             dataGridView.TabIndex = 1;
             // 
             // panel
@@ -107,7 +107,7 @@
             panel.Dock = DockStyle.Top;
             panel.Location = new Point(0, 24);
             panel.Name = "panel";
-            panel.Size = new Size(584, 29);
+            panel.Size = new Size(755, 29);
             panel.TabIndex = 2;
             // 
             // buttonEdit
@@ -119,7 +119,6 @@
             buttonEdit.TabIndex = 4;
             buttonEdit.Text = "Изменить";
             buttonEdit.UseVisualStyleBackColor = true;
-            buttonEdit.Click += this.buttonEdit_Click;
             // 
             // buttonDelete
             // 
@@ -130,7 +129,6 @@
             buttonDelete.TabIndex = 3;
             buttonDelete.Text = "Удалить";
             buttonDelete.UseVisualStyleBackColor = true;
-            buttonDelete.Click += buttonDelete_Click;
             // 
             // buttonAdd
             // 
@@ -141,7 +139,6 @@
             buttonAdd.TabIndex = 2;
             buttonAdd.Text = "Добавить";
             buttonAdd.UseVisualStyleBackColor = true;
-            buttonAdd.Click += this.buttonAdd_Click;
             // 
             // dateTimePicker1
             // 
@@ -165,7 +162,7 @@
             // 
             AutoScaleDimensions = new SizeF(7F, 15F);
             AutoScaleMode = AutoScaleMode.Font;
-            ClientSize = new Size(584, 301);
+            ClientSize = new Size(755, 301);
             Controls.Add(panel);
             Controls.Add(dataGridView);
             Controls.Add(menuStrip);
@@ -173,6 +170,7 @@
             MinimumSize = new Size(600, 340);
             Name = "FormMain";
             Text = "Записи посещений";
+            Load += FormMain_Load;
             menuStrip.ResumeLayout(false);
             menuStrip.PerformLayout();
             ((System.ComponentModel.ISupportInitialize)dataGridView).EndInit();

Medical/MedicalView/FormMain.cs

@@ -1,14 +1,4 @@
-using System;
+namespace MedicalView.Visits
-using System.Collections.Generic;
-using System.ComponentModel;
-using System.Data;
-using System.Drawing;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-using System.Windows.Forms;
-
-namespace MedicalView.Visits
 {
     public partial class FormMain : Form
     {
@@ -17,7 +7,7 @@ namespace MedicalView.Visits
             InitializeComponent();
         }
 
-        private void buttonDelete_Click(object sender, EventArgs e)
+        private void FormMain_Load(object sender, EventArgs e)
         {
 
         }

Medical/MedicalView/Program.cs

@@ -1,3 +1,5 @@
+using MedicalView.Visits;
+
 namespace MedicalView
 {
     internal static class Program
@@ -11,7 +13,7 @@ namespace MedicalView
             // To customize application configuration such as set high DPI settings or default font,
             // see https://aka.ms/applicationconfiguration.
             ApplicationConfiguration.Initialize();
-            Application.Run(new Form1());
+            Application.Run(new FormMain());
         }
     }
 }