diff --git a/AndDietCokeContracts/AndDietCokeContracts/AndDietCokeContracts.csproj b/AndDietCokeContracts/AndDietCokeContracts/AndDietCokeContracts.csproj
index cfadb03..4c18759 100644
--- a/AndDietCokeContracts/AndDietCokeContracts/AndDietCokeContracts.csproj
+++ b/AndDietCokeContracts/AndDietCokeContracts/AndDietCokeContracts.csproj
@@ -4,6 +4,7 @@
     <TargetFramework>net7.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
+    <LangVersion>preview</LangVersion>
   </PropertyGroup>
 
 </Project>
diff --git a/AndDietCokeContracts/AndDietCokeContracts/DataModels/BuyerDataModel.cs b/AndDietCokeContracts/AndDietCokeContracts/DataModels/BuyerDataModel.cs
new file mode 100644
index 0000000..0ad40bc
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/DataModels/BuyerDataModel.cs
@@ -0,0 +1,34 @@
+using AndDietCokeContracts.Extensions;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Numerics;
+using System.Text;
+using System.Text.RegularExpressions;
+using System.Threading.Tasks;
+using static System.Runtime.InteropServices.JavaScript.JSType;
+using System.Xml;
+using AndDietCokeContracts.Infrastrusture;
+using AndDietCokeContracts.Exceptions;
+
+namespace AndDietCokeContracts.DataModels;
+
+public class BuyerDataModel(string id, string fio, string phoneNumber) : IValidation
+{
+    public string Id { get; private set; } = id;
+    public string FIO { get; private set; } = fio;
+    public string PhoneNumber { get; private set; } = phoneNumber;
+    public void Validate()
+    {
+        if (Id.IsEmpty())
+            throw new ValidationException("Field Id is empty");
+        if (!Id.IsGuid())
+            throw new ValidationException("The value in the field Id is not a unique identifier");
+        if (FIO.IsEmpty())
+            throw new ValidationException("Field FIO is empty");
+        if (PhoneNumber.IsEmpty())
+            throw new ValidationException("Field PhoneNumber is empty");
+        if (!Regex.IsMatch(PhoneNumber, @"^((8|\+7)[\- ]?)?(\(?\d{3}\)?[\- ]?)?[\d\- ]{7,10}$"))
+            throw new ValidationException("Field PhoneNumber is not a phone number");
+    }
+}
diff --git a/AndDietCokeContracts/AndDietCokeContracts/DataModels/DishDataModel.cs b/AndDietCokeContracts/AndDietCokeContracts/DataModels/DishDataModel.cs
new file mode 100644
index 0000000..752eabd
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/DataModels/DishDataModel.cs
@@ -0,0 +1,35 @@
+using AndDietCokeContracts.Extensions;
+using AndDietCokeContracts.Infrastrusture;
+using AndDietCokeContracts.Exceptions;
+using AndDietCokeContracts.Enums;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Xml;
+
+namespace AndDietCokeContracts.DataModels;
+
+public class DishDataModel(string id, string dishName, DishType
+dishType, double price, bool isDeleted) : IValidation
+{
+    public string Id { get; private set; } = id;
+    public string DishName { get; private set; } = dishName;
+    public DishType DishType { get; private set; } = dishType;
+    public double Price { get; private set; } = price;
+    public bool IsDeleted { get; private set; } = isDeleted;
+    public void Validate()
+    {
+        if (Id.IsEmpty())
+            throw new ValidationException("Field Id is empty");
+        if (!Id.IsGuid())
+            throw new ValidationException("The value in the field Id is not a unique identifier");
+        if (DishName.IsEmpty())
+            throw new ValidationException("Field DishName is empty");
+        if (DishType == DishType.None)
+            throw new ValidationException("Field DishType is empty");
+        if (Price <= 0)
+            throw new ValidationException("Field Price is less than or equal to 0");
+}
+}
diff --git a/AndDietCokeContracts/AndDietCokeContracts/DataModels/DishHistoryDataModel.cs b/AndDietCokeContracts/AndDietCokeContracts/DataModels/DishHistoryDataModel.cs
new file mode 100644
index 0000000..1b22ca2
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/DataModels/DishHistoryDataModel.cs
@@ -0,0 +1,27 @@
+using AndDietCokeContracts.Extensions;
+using AndDietCokeContracts.Infrastrusture;
+using AndDietCokeContracts.Exceptions;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace AndDietCokeContracts.DataModels;
+
+public class DishHistoryDataModel(string dishId, double oldPrice) : IValidation
+{
+    public string DishId { get; private set; } = dishId;
+    public double OldPrice { get; private set; } = oldPrice;
+    public DateTime ChangeDate { get; private set; } = DateTime.UtcNow;
+    public void Validate()
+    {
+        if (DishId.IsEmpty())
+            throw new ValidationException("Field DishId is empty");
+        if (!DishId.IsGuid())
+            throw new ValidationException("The value in the field DishId is not a unique identifier");
+    if (OldPrice <= 0)
+            throw new ValidationException("Field OldPrice is less than or equal to 0");
+    }
+}
+
diff --git a/AndDietCokeContracts/AndDietCokeContracts/DataModels/OrderDataModel.cs b/AndDietCokeContracts/AndDietCokeContracts/DataModels/OrderDataModel.cs
new file mode 100644
index 0000000..81dddd2
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/DataModels/OrderDataModel.cs
@@ -0,0 +1,30 @@
+using AndDietCokeContracts.Exceptions;
+using AndDietCokeContracts.Extensions;
+using AndDietCokeContracts.Infrastrusture;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace AndDietCokeContracts.DataModels;
+
+public class OrderDataModel(string orderId, string dishId, int count) : IValidation
+{
+    public string OrderId { get; private set; } = orderId;
+    public string DishId { get; private set; } = dishId;
+    public int Count { get; private set; } = count;
+    public void Validate()
+    {
+        if (OrderId.IsEmpty())
+            throw new ValidationException("Field OrderId is empty");
+        if (!OrderId.IsGuid())
+            throw new ValidationException("The value in the field OrderId is not a unique identifier");
+        if (DishId.IsEmpty())
+            throw new ValidationException("Field DishId is empty");
+        if (!DishId.IsGuid())
+            throw new ValidationException("The value in the field DishId is not a unique identifier");
+        if (Count <= 0)
+            throw new ValidationException("Field Count is less than or equal to 0");
+    }
+}
diff --git a/AndDietCokeContracts/AndDietCokeContracts/DataModels/PostDataModel.cs b/AndDietCokeContracts/AndDietCokeContracts/DataModels/PostDataModel.cs
new file mode 100644
index 0000000..69e6c1a
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/DataModels/PostDataModel.cs
@@ -0,0 +1,42 @@
+using AndDietCokeContracts.Enums;
+using AndDietCokeContracts.Extensions;
+using AndDietCokeContracts.Infrastrusture;
+using AndDietCokeContracts.Exceptions;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Xml;
+
+namespace AndDietCokeContracts.DataModels;
+
+public class PostDataModel(string id, string postId, string postName, PostType
+postType, double salary, bool isActual, DateTime changeDate) : IValidation
+{
+    public string Id { get; private set; } = id;
+    public string PostId { get; private set; } = postId;
+    public string PostName { get; private set; } = postName;
+    public PostType PostType { get; private set; } = postType;
+    public double Salary { get; private set; } = salary;
+    public bool IsActual { get; private set; } = isActual;
+    public DateTime ChangeDate { get; private set; } = changeDate;
+    public void Validate()
+    {
+        if (Id.IsEmpty())
+            throw new ValidationException("Field Id is empty");
+        if (!Id.IsGuid())
+            throw new ValidationException("The value in the field Id is not a unique identifier");
+        if (PostId.IsEmpty())
+            throw new ValidationException("Field PostId is empty");
+        if (!PostId.IsGuid())
+            throw new ValidationException("The value in the field PostId is not a unique identifier");
+        if (PostName.IsEmpty())
+            throw new ValidationException("Field PostName is empty");
+        if (PostType == PostType.None)
+            throw new ValidationException("Field PostType is empty");
+        if (Salary <= 0)
+            throw new ValidationException("Field Salary is empty");
+    }
+}
+
diff --git a/AndDietCokeContracts/AndDietCokeContracts/DataModels/SalaryDataModel.cs b/AndDietCokeContracts/AndDietCokeContracts/DataModels/SalaryDataModel.cs
new file mode 100644
index 0000000..de1aef6
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/DataModels/SalaryDataModel.cs
@@ -0,0 +1,28 @@
+using AndDietCokeContracts.Exceptions;
+using AndDietCokeContracts.Extensions;
+using AndDietCokeContracts.Infrastrusture;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace AndDietCokeContracts.DataModels;
+
+public class SalaryDataModel(string workerId, DateTime salaryDate, double
+workerSalary) : IValidation
+{
+    public string WorkerId { get; private set; } = workerId;
+    public DateTime SalaryDate { get; private set; } = salaryDate;
+    public double Salary { get; private set; } = workerSalary;
+    public void Validate()
+    {
+        if (WorkerId.IsEmpty())
+            throw new ValidationException("Field WorkerId is empty");
+        if (!WorkerId.IsGuid())
+            throw new ValidationException("The value in the field WorkerId is not a unique identifier");
+        if (Salary <= 0)
+            throw new ValidationException("Field Salary is less than or equal to 0");
+    }
+}
+
diff --git a/AndDietCokeContracts/AndDietCokeContracts/DataModels/SaleDataModel.cs b/AndDietCokeContracts/AndDietCokeContracts/DataModels/SaleDataModel.cs
new file mode 100644
index 0000000..71f8437
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/DataModels/SaleDataModel.cs
@@ -0,0 +1,41 @@
+using AndDietCokeContracts.Enums;
+using AndDietCokeContracts.Exceptions;
+using AndDietCokeContracts.Extensions;
+using AndDietCokeContracts.Infrastrusture;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Xml;
+
+namespace AndDietCokeContracts.DataModels;
+
+public class SaleDataModel(string id, string workerId, string? buyerId, double sum, IsConstantClient isConstantClient, bool isCancel, List<OrderDataModel> dishes) : IValidation
+{
+    public string Id { get; private set; } = id;
+    public string WorkerId { get; private set; } = workerId;
+    public string? BuyerId { get; private set; } = buyerId;
+    public DateTime SaleDate { get; private set; } = DateTime.UtcNow;
+    public double Sum { get; private set; } = sum;
+    public IsConstantClient IsConstantClient { get; private set; } = isConstantClient;
+    public bool IsCancel { get; private set; } = isCancel;
+    public List<OrderDataModel> Dishes { get; private set; } = dishes;
+    public void Validate()
+    {
+        if (Id.IsEmpty())
+            throw new ValidationException("Field Id is empty");
+        if (!Id.IsGuid())
+            throw new ValidationException("The value in the field Id is not a unique identifier");
+        if (WorkerId.IsEmpty())
+            throw new ValidationException("Field WorkerId is empty");
+        if (!WorkerId.IsGuid())
+            throw new ValidationException("The value in the field WorkerId is not a unique identifier");
+        if (!BuyerId?.IsGuid() ?? !BuyerId?.IsEmpty() ?? false)
+            throw new ValidationException("The value in the field BuyerId is not a unique identifier");
+        if (Sum <= 0)
+            throw new ValidationException("Field Sum is less than or equal to 0");
+        if ((Dishes?.Count ?? 0) == 0)
+            throw new ValidationException("The sale must include dishes");
+}
+}
diff --git a/AndDietCokeContracts/AndDietCokeContracts/DataModels/WorkerDataModel.cs b/AndDietCokeContracts/AndDietCokeContracts/DataModels/WorkerDataModel.cs
new file mode 100644
index 0000000..cf54679
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/DataModels/WorkerDataModel.cs
@@ -0,0 +1,42 @@
+using AndDietCokeContracts.Exceptions;
+using AndDietCokeContracts.Extensions;
+using AndDietCokeContracts.Infrastrusture;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Xml;
+using static System.Runtime.InteropServices.JavaScript.JSType;
+
+namespace AndDietCokeContracts.DataModels;
+
+public class WorkerDataModel(string id, string fio, string postId, DateTime
+birthDate, DateTime employmentDate, bool isDeleted) : IValidation
+{
+    public string Id { get; private set; } = id;
+    public string FIO { get; private set; } = fio;
+    public string PostId { get; private set; } = postId;
+    public DateTime BirthDate { get; private set; } = birthDate;
+    public DateTime EmploymentDate { get; private set; } = employmentDate;
+    public bool IsDeleted { get; private set; } = isDeleted;
+    public void Validate()
+    {
+        if (Id.IsEmpty())
+            throw new ValidationException("Field Id is empty");
+        if (!Id.IsGuid())
+            throw new ValidationException("The value in the field Id is not a unique identifier");
+        if (FIO.IsEmpty())
+            throw new ValidationException("Field FIO is empty");
+        if (PostId.IsEmpty())
+            throw new ValidationException("Field PostId is empty");
+        if (!PostId.IsGuid())
+            throw new ValidationException("The value in the field PostId is not a unique identifier");
+        if (BirthDate.Date > DateTime.Now.AddYears(-16).Date)
+            throw new ValidationException($"Minors cannot be hired (BirthDate = { BirthDate.ToShortDateString() })");
+        if (EmploymentDate.Date < BirthDate.Date)
+            throw new ValidationException("The date of employment cannot be less than the date of birth");
+        if ((EmploymentDate - BirthDate).TotalDays / 365 < 16) //EmploymentDate.Year - BirthDate.Year
+            throw new ValidationException($"Minors cannot be hired (EmploymentDate - { EmploymentDate.ToShortDateString() }, BirthDate - { BirthDate.ToShortDateString()})");
+    }
+}
diff --git a/AndDietCokeContracts/AndDietCokeContracts/Enums/DishType.cs b/AndDietCokeContracts/AndDietCokeContracts/Enums/DishType.cs
new file mode 100644
index 0000000..eadf575
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/Enums/DishType.cs
@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace AndDietCokeContracts.Enums;
+
+public enum DishType
+{
+    None = 0,
+    Base = 1,
+    Dessert = 2,
+    Drink = 3
+}
diff --git a/AndDietCokeContracts/AndDietCokeContracts/Enums/IsConstantClient.cs b/AndDietCokeContracts/AndDietCokeContracts/Enums/IsConstantClient.cs
new file mode 100644
index 0000000..d464937
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/Enums/IsConstantClient.cs
@@ -0,0 +1,14 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.Tracing;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace AndDietCokeContracts.Enums;
+
+public enum IsConstantClient
+{
+    None = 0,
+    ConstantClient = 1
+}
diff --git a/AndDietCokeContracts/AndDietCokeContracts/Enums/PostType.cs b/AndDietCokeContracts/AndDietCokeContracts/Enums/PostType.cs
new file mode 100644
index 0000000..b643f89
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/Enums/PostType.cs
@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace AndDietCokeContracts.Enums;
+
+public enum PostType
+{
+    None = 0,
+    Waiter = 1,
+    Chef = 2,
+    Packer = 3
+}
+
diff --git a/AndDietCokeContracts/AndDietCokeContracts/Exceptions/ValidationException.cs b/AndDietCokeContracts/AndDietCokeContracts/Exceptions/ValidationException.cs
new file mode 100644
index 0000000..3d99264
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/Exceptions/ValidationException.cs
@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace AndDietCokeContracts.Exceptions;
+
+public class ValidationException : Exception
+{
+    public ValidationException(string message) : base(message) { }
+}
diff --git a/AndDietCokeContracts/AndDietCokeContracts/Extensions/StringExtensions.cs b/AndDietCokeContracts/AndDietCokeContracts/Extensions/StringExtensions.cs
new file mode 100644
index 0000000..3e217d7
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/Extensions/StringExtensions.cs
@@ -0,0 +1,19 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace AndDietCokeContracts.Extensions;
+
+public static class StringExtensions
+{
+    public static bool IsEmpty(this string str)
+    {
+        return string.IsNullOrWhiteSpace(str);
+    }
+    public static bool IsGuid(this string str)
+    {
+        return Guid.TryParse(str, out _);
+    }
+}
diff --git a/AndDietCokeContracts/AndDietCokeContracts/Infrastrusture/IValidation.cs b/AndDietCokeContracts/AndDietCokeContracts/Infrastrusture/IValidation.cs
new file mode 100644
index 0000000..9e5791c
--- /dev/null
+++ b/AndDietCokeContracts/AndDietCokeContracts/Infrastrusture/IValidation.cs
@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace AndDietCokeContracts.Infrastrusture;
+
+public interface IValidation
+{
+    void Validate();
+}