public void AddNewCustomers(params Customer[] customers)
       {
           using (ISession session = _factory.OpenSession())
           {
               using (ITransaction transaction = session.BeginTransaction())
               {
                   foreach (var data in customers)
                       session.Save(data);

                   session.Flush();

                   transaction.Commit();
               }
           }
       }

using System.Collections.Generic;
using System.Linq;
using NHibernate;
using NHibernate.Linq;
using NHSample1.Domain;

namespace ConsoleTestApplication
{
   class CLinqTest : NHibernateContext
   {  }
}

using System.Collections.Generic;
using System.Linq;
using NHibernate;
using NHibernate.Linq;
using NHSample1.Domain;

namespace ConsoleTestApplication
{
   class CLinqTest : NHibernateContext
   {
       ISessionFactory _factory;

       public CLinqTest(ISessionFactory factory)
       {
           _factory = factory;
       }

       public List<Customer> GetAllCustomers()
       {
           using (ISession session = _factory.OpenSession())
           {
               var query = from x in session.Linq<Customer>() select x;
               return query.ToList();
           }
       }
   }
}

       static void Main(string[] args)
       {
           using (ISessionFactory session = Config.CreateSessionFactory(
                 MsSqlConfiguration
                    .MsSql2008
                    .ConnectionString("Data Source=(local);Initial Catalog=HelloNHibernate;Integrated Security = true")
                    .ShowSql()
               ))
           {

               var customer1 = new Customer()
               {
                   FirstName = "Vahid",
                   LastName = "Nasiri",
                   AddressLine1 = "Addr1",
                   AddressLine2 = "Addr2",
                   PostalCode = "1234",
                   City = "Tehran",
                   CountryCode = "IR"
               };

               var customer2 = new Customer()
               {
                   FirstName = "Ali",
                   LastName = "Hasani",
                   AddressLine1 = "Addr..1",
                   AddressLine2 = "Addr..2",
                   PostalCode = "4321",
                   City = "Shiraz",
                   CountryCode = "IR"
               };

               var customer3 = new Customer()
               {
                   FirstName = "Mohsen",
                   LastName = "Shams",
                   AddressLine1 = "Addr...1",
                   AddressLine2 = "Addr...2",
                   PostalCode = "5678",
                   City = "Ahwaz",
                   CountryCode = "IR"
               };

               CDbOperations db = new CDbOperations(session);
               db.AddNewCustomers(customer1, customer2, customer3);

               CLinqTest lt = new CLinqTest(session);
               foreach (Customer customer in lt.GetAllCustomers())
               {
                   Console.WriteLine("Customer: LastName = {0}", customer.LastName);
               }
           }

           Console.WriteLine("Press a key...");
           Console.ReadKey();

       }

       public List<Customer> GetCustomersByCity(string city)
       {
           using (ISession session = _factory.OpenSession())
           {
               var query = from x in session.Linq<Customer>()
                           where x.City == city
                           select x;
               return query.ToList();
           }
       }

               foreach (Customer customer in lt.GetCustomersByCity("Shiraz"))
               {
                   Console.WriteLine("Customer: LastName = {0}", customer.LastName);
               }

using System.Linq;
using NHibernate;
using NHibernate.Linq;
using NHSample1.Domain;

namespace ConsoleTestApplication
{
   class SampleContext : NHibernateContext
   {
       public SampleContext(ISession session)
           : base(session)
       { }

       public IOrderedQueryable<Customer> Customers
       {
           get { return Session.Linq<Customer>(); }
       }

       public IOrderedQueryable<Employee> Employees
       {
           get { return Session.Linq<Employee>(); }
       }

       public IOrderedQueryable<Order> Orders
       {
           get { return Session.Linq<Order>(); }
       }

       public IOrderedQueryable<OrderItem> OrderItems
       {
           get { return Session.Linq<OrderItem>(); }
       }

       public IOrderedQueryable<Product> Products
       {
           get { return Session.Linq<Product>(); }
       }
   }
}

using System.Collections.Generic;
using System.Linq;
using NHibernate;
using NHSample1.Domain;

namespace ConsoleTestApplication
{
   class CSampleContextTest
   {
       ISessionFactory _factory;

       public CSampleContextTest(ISessionFactory factory)
       {
           _factory = factory;
       }

       public List<Customer> GetCustomersByCity(string city)
       {
           using (ISession session = _factory.OpenSession())
           {
               using (SampleContext db = new SampleContext(session))
               {
                   var query = from x in db.Customers
                               where x.City == city
                               select x;
                   return query.ToList();
               }
           }
       }
   }
}

Change this section ...

<PropertyGroup>
    <TargetFramework>netcoreapp2.2</TargetFramework>
    <AspNetCoreHostingModel>InProcess</AspNetCoreHostingModel>
  </PropertyGroup>

to the following ...

<PropertyGroup>
    <TargetFramework>netcoreapp2.2</TargetFramework>
    <AspNetCoreHostingModel>OutOfProcess</AspNetCoreHostingModel>
    <AspNetCoreModuleName>AspNetCoreModule</AspNetCoreModuleName>
  </PropertyGroup>