diff --git a/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/CustomerDataModel.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/CustomerDataModel.cs
new file mode 100644
index 0000000..0087a85
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/CustomerDataModel.cs
@@ -0,0 +1,33 @@
+using System.Text.RegularExpressions;
+using TwoFromTheCaseContracts.Exceptions;
+using TwoFromTheCaseContracts.Extensions;
+using TwoFromTheCaseContracts.Infrastructure;
+
+namespace TwoFromTheCaseContracts.DataModels;
+
+public class CustomerDataModel(string id, string name, string phoneNumber) : IValidation
+{
+    public string Id { get; private set; } = id;
+
+    public string Name { get; private set; } = name;
+
+    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 (Name.IsEmpty())
+            throw new ValidationException("Field Name is empty");
+
+        if (PhoneNumber.IsEmpty())
+            throw new ValidationException("Field PhoneNumber is empty");
+
+        if (!Regex.IsMatch(PhoneNumber, @"^((\+7|7|8)+([0-9]){10})$"))
+            throw new ValidationException("Field PhoneNumber is not a phone number");
+    }
+}
diff --git a/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/PostDataModel.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/PostDataModel.cs
new file mode 100644
index 0000000..47c9608
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/PostDataModel.cs
@@ -0,0 +1,47 @@
+using TwoFromTheCaseContracts.Enums;
+using TwoFromTheCaseContracts.Exceptions;
+using TwoFromTheCaseContracts.Extensions;
+using TwoFromTheCaseContracts.Infrastructure;
+
+namespace TwoFromTheCaseContracts.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");
+    }
+}
\ No newline at end of file
diff --git a/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/PremisesDataModel.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/PremisesDataModel.cs
new file mode 100644
index 0000000..20406bd
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/PremisesDataModel.cs
@@ -0,0 +1,40 @@
+using TwoFromTheCaseContracts.Enums;
+using TwoFromTheCaseContracts.Exceptions;
+using TwoFromTheCaseContracts.Extensions;
+using TwoFromTheCaseContracts.Infrastructure;
+
+namespace TwoFromTheCaseContracts.DataModels;
+
+public class PremisesDataModel(string id, string premisesName, PremisesType premisesType, string customerId, bool isDeleted) : IValidation
+{
+    public string Id { get; private set; } = id;
+
+    public string PremisesName { get; private set; } = premisesName;
+
+    public PremisesType PremisesType { get; private set; } = premisesType;
+
+    public string CustomerId { get; private set; } = customerId;
+
+    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 (PremisesName.IsEmpty())
+            throw new ValidationException("Field PremisesName is empty");
+
+        if (PremisesType == PremisesType.None)
+            throw new ValidationException("Field PremisesType is empty");
+
+        if (CustomerId.IsEmpty())
+            throw new ValidationException("Field CustomerId is empty");
+
+        if (!CustomerId.IsGuid())
+            throw new ValidationException("The value in the field CustomerId is not a unique identifier");
+    }
+}
diff --git a/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/SalaryDataModel.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/SalaryDataModel.cs
new file mode 100644
index 0000000..f8ff497
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/SalaryDataModel.cs
@@ -0,0 +1,26 @@
+using TwoFromTheCaseContracts.Exceptions;
+using TwoFromTheCaseContracts.Extensions;
+using TwoFromTheCaseContracts.Infrastructure;
+
+namespace TwoFromTheCaseContracts.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/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkDataModel.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkDataModel.cs
new file mode 100644
index 0000000..710814c
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkDataModel.cs
@@ -0,0 +1,41 @@
+using TwoFromTheCaseContracts.Exceptions;
+using TwoFromTheCaseContracts.Extensions;
+using TwoFromTheCaseContracts.Infrastructure;
+
+namespace TwoFromTheCaseContracts.DataModels;
+
+public class WorkDataModel(string id, string premisesId, double price, bool isCancel, List<WorkerWorkDataModel> workers) : IValidation
+{
+    public string Id { get; private set; } = id;
+
+    public string PremisesId { get; private set; } = premisesId;
+
+    public double Price { get; private set; } = price;
+
+    public DateTime SaleDate { get; private set; } = DateTime.UtcNow;
+
+    public bool IsCancel { get; private set; } = isCancel;
+
+    public List<WorkerWorkDataModel> Workers { get; private set; } = workers;
+
+    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 (PremisesId.IsEmpty())
+            throw new ValidationException("Field PremisesId is empty");
+
+        if (!PremisesId.IsGuid())
+            throw new ValidationException("The value in the field PremisesId is not a unique identifier");
+
+        if (Price <= 0)
+            throw new ValidationException("Field Price is less than or equal to 0");
+
+        if ((Workers?.Count ?? 0) == 0)
+            throw new ValidationException("The sale must include workers");
+    }
+}
diff --git a/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkHistoryDataModel.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkHistoryDataModel.cs
new file mode 100644
index 0000000..d2c2f89
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkHistoryDataModel.cs
@@ -0,0 +1,26 @@
+using TwoFromTheCaseContracts.Exceptions;
+using TwoFromTheCaseContracts.Extensions;
+using TwoFromTheCaseContracts.Infrastructure;
+
+namespace TwoFromTheCaseContracts.DataModels;
+
+public class WorkHistoryDataModel(string WorkId, double oldPrice) : IValidation
+{
+    public string WorkId { get; private set; } = WorkId;
+
+    public double OldPrice { get; private set; } = oldPrice;
+
+    public DateTime ChangeDate { get; private set; } = DateTime.UtcNow;
+
+    public void Validate()
+    {
+        if (WorkId.IsEmpty())
+            throw new ValidationException("Field WorkId is empty");
+
+        if (!WorkId.IsGuid())
+            throw new ValidationException("The value in the field WorkId is not a unique identifier");
+
+        if (OldPrice <= 0)
+            throw new ValidationException("Field OldPrice is less than or equal to 0");
+    }
+}
diff --git a/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkerDataModel.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkerDataModel.cs
new file mode 100644
index 0000000..221a63f
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkerDataModel.cs
@@ -0,0 +1,47 @@
+using TwoFromTheCaseContracts.Exceptions;
+using TwoFromTheCaseContracts.Extensions;
+using TwoFromTheCaseContracts.Infrastructure;
+
+namespace TwoFromTheCaseContracts.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()})");
+    }
+}
\ No newline at end of file
diff --git a/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkerWorkDataModel.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkerWorkDataModel.cs
new file mode 100644
index 0000000..2ffeda3
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/DataModels/WorkerWorkDataModel.cs
@@ -0,0 +1,27 @@
+using TwoFromTheCaseContracts.Exceptions;
+using TwoFromTheCaseContracts.Extensions;
+using TwoFromTheCaseContracts.Infrastructure;
+
+namespace TwoFromTheCaseContracts.DataModels;
+
+public class WorkerWorkDataModel(string workerId, string workId) : IValidation
+{
+    public string WorkerId { get; private set; } = workerId;
+
+    public string WorkId { get; private set; } = workId;
+
+    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 (WorkId.IsEmpty())
+            throw new ValidationException("Field WorkId is empty");
+
+        if (!WorkId.IsGuid())
+            throw new ValidationException("The value in the field WorkId is not a unique identifier");
+    }
+}
diff --git a/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Enums/PostType.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Enums/PostType.cs
new file mode 100644
index 0000000..3596db4
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Enums/PostType.cs
@@ -0,0 +1,11 @@
+namespace TwoFromTheCaseContracts.Enums;
+
+public enum PostType
+{
+    None = 0,
+    Plasterer = 1,
+    Painter = 2,
+    Carpenter = 3,
+    Plumber = 4,
+    Electrician = 5
+}
diff --git a/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Enums/PremisesType.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Enums/PremisesType.cs
new file mode 100644
index 0000000..09bf298
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Enums/PremisesType.cs
@@ -0,0 +1,8 @@
+namespace TwoFromTheCaseContracts.Enums;
+
+public enum PremisesType
+{
+    None = 0,
+    Residential = 1,
+    Commercial = 2
+}
diff --git a/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Exceptions/ValidationException.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Exceptions/ValidationException.cs
new file mode 100644
index 0000000..a38dbda
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Exceptions/ValidationException.cs
@@ -0,0 +1,5 @@
+namespace TwoFromTheCaseContracts.Exceptions;
+
+public class ValidationException(string message) : Exception(message)
+{
+}
diff --git a/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Extensions/StringExtensions.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Extensions/StringExtensions.cs
new file mode 100644
index 0000000..37b0218
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Extensions/StringExtensions.cs
@@ -0,0 +1,14 @@
+namespace TwoFromTheCaseContracts.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/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Infrastructure/IValidation.cs b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Infrastructure/IValidation.cs
new file mode 100644
index 0000000..209b796
--- /dev/null
+++ b/TwoFromTheCaseContracts/TwoFromTheCaseContracts/Infrastructure/IValidation.cs
@@ -0,0 +1,6 @@
+namespace TwoFromTheCaseContracts.Infrastructure;
+
+public interface IValidation
+{
+    void Validate();
+}