сделал свою очень сложную работу

CarCenterDataModels/CarCenterDataModels.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>net7.0</TargetFramework>

CarCenterDataModels/HelperInterfaces/IId.cs

@@ -0,0 +1,7 @@
+namespace CarCenterDataModels.HelperInterfaces
+{
+    public interface IId
+    {
+        int Id { get; }
+    }
+}

CarCenterDataModels/HelperInterfaces/IUser.cs

@@ -0,0 +1,14 @@
+namespace CarCenterDataModels.HelperInterfaces
+{
+    public interface IUser : IId
+    {
+        string FirstName { get; }
+        string LastName { get; }
+
+        string Login { get; }
+
+        string Password { get; }
+
+        string PhoneNumber { get; }
+    }
+}

CarCenterDataModels/IAccountModel.cs

@@ -0,0 +1,10 @@
+using CarCenterDataModels.HelperInterfaces;
+
+namespace CarCenterDataModels
+{
+    public interface IAccountModel : IId
+    {
+        int ClientByCarId { get; }
+        double Price { get; }
+    }
+}

CarCenterDataModels/ICarModel.cs

@@ -0,0 +1,16 @@
+using CarCenterDataModels.HelperInterfaces;
+using CarCenterDataModels.ProxyModels;
+
+namespace CarCenterDataModels
+{
+    public interface ICarModel : IId
+    {
+        int ImplementerId { get; }
+
+        string Name { get; }
+
+        double Price { get; }
+
+        Dictionary<int, ClientByCarModel> ClientsModel { get; }
+    }
+}

CarCenterDataModels/IImplementerModel.cs

@@ -0,0 +1,8 @@
+using CarCenterDataModels.HelperInterfaces;
+
+namespace CarCenterDataModels
+{
+    public interface IImplementerModel : IUser
+    {
+    }
+}

CarCenterDataModels/ProxyModels/ClientByCarModel.cs

@@ -0,0 +1,11 @@
+namespace CarCenterDataModels.ProxyModels
+{
+    public class ClientByCarModel
+    {
+        public virtual int Id { get; set; }
+        public virtual int ClientId { get; set; }
+        public virtual int CarId { get; set; }
+
+        public virtual DateTime DateOfClient { get; set; }
+    }
+}