изменила и добавила модели данных - убрала общий айдишник

BeautySalon/BeautySalon/FormMain.Designer.cs

@@ -28,12 +28,43 @@
         /// </summary>
         private void InitializeComponent()
         {
-            this.components = new System.ComponentModel.Container();
-            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
-            this.ClientSize = new System.Drawing.Size(800, 450);
-            this.Text = "FormMain";
+            comboBoxService = new ComboBox();
+            label1 = new Label();
+            SuspendLayout();
+            // 
+            // comboBoxService
+            // 
+            comboBoxService.FormattingEnabled = true;
+            comboBoxService.Location = new Point(310, 209);
+            comboBoxService.Name = "comboBoxService";
+            comboBoxService.Size = new Size(227, 28);
+            comboBoxService.TabIndex = 0;
+            // 
+            // label1
+            // 
+            label1.AutoSize = true;
+            label1.Location = new Point(350, 253);
+            label1.Name = "label1";
+            label1.Size = new Size(124, 20);
+            label1.TabIndex = 1;
+            label1.Text = "Выберите услугу";
+            // 
+            // FormMain
+            // 
+            AutoScaleDimensions = new SizeF(8F, 20F);
+            AutoScaleMode = AutoScaleMode.Font;
+            ClientSize = new Size(817, 456);
+            Controls.Add(label1);
+            Controls.Add(comboBoxService);
+            Name = "FormMain";
+            Text = "FormMain";
+            ResumeLayout(false);
+            PerformLayout();
         }
 
         #endregion
+
+        private ComboBox comboBoxService;
+        private Label label1;
     }
 }

BeautySalon/BeautySalonDBModels/ICheque.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace BeautySalonDBModels
+{
+    public interface ICheque
+    {
+        int ChequeId { get; }
+        int ClientId { get; }
+        string ReceptionId { get; }
+    }
+}

BeautySalon/BeautySalonDBModels/IClient.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace BeautySalonDBModels
+{
+    public interface IClient 
+    {
+        int ClientId { get; }
+        string FIO {  get; }
+        int Age { get; }
+    }
+}

BeautySalon/BeautySalonDBModels/IMaster.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace BeautySalonDBModels
+{
+    public interface IMaster 
+    {
+        int MasterId { get; }
+        int SpecialisationId { get; }
+        string FIO {  get; }
+    }
+}

BeautySalon/BeautySalonDBModels/IReception.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace BeautySalonDBModels
+{
+    public interface IReception 
+    {
+        int ReceptionId { get; }
+        int MasterId { get; }
+        int ServiceId { get; }
+        DateTime DateReception { get; }
+    }
+}

BeautySalon/BeautySalonDBModels/IService.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace BeautySalonDBModels
+{
+    public interface IService 
+    {
+        int ServiceId { get; }
+        string ServiceName { get; }
+        double Price { get; }
+        int SpecialisationId { get; }
+    }
+}

BeautySalon/BeautySalonDBModels/ISpecialisation.cs

@@ -0,0 +1,14 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace BeautySalonDBModels
+{
+    public interface ISpecialisation 
+    {
+        int SpecialisationId { get; }
+        string Name { get; }
+    }
+}