Using a PagedList with a ViewModel ASP Net MVC

Question

I m trying to using a PagedList in my ASP Net application and I found this example on the Microsoft website http   www asp net mvc tutorials getting-started-with-ef-using-mvc sorting-filtering-and-paging-with-the-entity-framework-in-an-asp-net-mvc-application  How is it possible to use a PagedList in a complex situation that uses a ViewModel  I m trying to add a PagedList without success to the Instructor example posted here  http   www asp net mvc tutorials getting-started-with-ef-using-mvc reading-related-data-with-the-entity-framework-in-an-asp-net-mvc-application  The problem is that the ViewModel is composed by classes and not simple fields  so I cannot convert the result with the ToPageList   method   This is the ViewModel structure   using System Collections Generic  using ContosoUniversity Models   namespace ContosoUniversity ViewModels       public class InstructorIndexData               public IEnumerable lt Instructor gt  Instructors   get  set            public IEnumerable lt Course gt  Courses   get  set            public IEnumerable lt Enrollment gt  Enrollments   get  set              I need to join the three tables into the ViewModel and display the result in a View

User · Answer

I figured out how to do this   I was building an application very similar to the example tutorial you discussed in your original question   Here s a snippet of the code that worked for me           int pageSize   4          int pageNumber    page    1             Used the following two formulas so that it doesn t round down on the returned integer         decimal totalPages     decimal  viewModel Teachers Count     decimal  pageSize                 ViewBag TotalPages   Math Ceiling totalPages               These next two functions could maybe be reduced to one function    would require some testing and building         viewModel Teachers   viewModel Teachers ToPagedList pageNumber  pageSize           ViewBag OnePageofTeachers   viewModel Teachers          ViewBag PageNumber   pageNumber           return View viewModel     I added   using PagedList    to my controller as the tutorial states   Now in my view my using statements etc at the top  NOTE i didnt change my using model statement    model CSHM ViewModels TeacherIndexData  using PagedList   using PagedList Mvc   lt link href    Content PagedList css  rel  stylesheet  type  text css    gt    and then at the bottom to build my paged list I used the following and it seems to work   I haven t yet built in the functionality for current sort  showing related data  filters  etc but i dont think it will be that difficult   Page  ViewBag PageNumber of  ViewBag TotalPages   Html PagedListPager  IPagedList ViewBag OnePageofTeachers  page   gt  Url Action  Index   new   page       Hope that works for you   Let me know if it works

User · Answer

I modified the code as follow   ViewModel  using System Collections Generic  using ContosoUniversity Models   namespace ContosoUniversity ViewModels       public class InstructorIndexData            public PagedList IPagedList lt Instructor gt  Instructors   get  set         public PagedList IPagedList lt Course gt  Courses   get  set         public PagedList IPagedList lt Enrollment gt  Enrollments   get  set              Controller         public ActionResult Index int  id  int  courseID int  InstructorPage int  CoursePage int  EnrollmentPage     int instructPageNumber    InstructorPage   1    int CoursePageNumber    CoursePage   1    int EnrollmentPageNumber    EnrollmentPage   1    var viewModel   new InstructorIndexData     viewModel Instructors   db Instructors      Include i   gt  i OfficeAssignment       Include i   gt  i Courses Select c   gt  c Department        OrderBy i   gt  i LastName  ToPagedList instructPageNumber 5     if  id    null         ViewBag InstructorID   id Value      viewModel Courses   viewModel Instructors Where          i   gt  i ID    id Value  Single   Courses ToPagedList CoursePageNumber 5        if  courseID    null         ViewBag CourseID   courseID Value      viewModel Enrollments   viewModel Courses Where          x   gt  x CourseID    courseID  Single   Enrollments ToPagedList EnrollmentPageNumber 5        return View viewModel       View   lt div gt     Page   Model Instructors PageCount  lt  Model Instructors PageNumber   0   Model Instructors PageNumber  of  Model Instructors PageCount      Html PagedListPager Model Instructors  page   gt  Url Action  Index   new  InstructorPage page      lt  div gt    I hope this would help you

User · Answer

As Chris suggested the reason you re using ViewModel doesn t stop you from using PagedList  You need to form a collection of your ViewModel objects that needs to be send to the view for paging over   Here is a step by step guide on how you can use PagedList for your viewmodel data   Your viewmodel  I have taken a simple example for brevity and you can easily modify it to fit your needs    public class QuestionViewModel           public int QuestionId   get  set            public string QuestionName   get  set        and the Index method of your controller will be something like  public ActionResult Index int  page         var questions   new                new QuestionViewModel   QuestionId   1  QuestionName    Question 1                new QuestionViewModel   QuestionId   1  QuestionName    Question 2                new QuestionViewModel   QuestionId   1  QuestionName    Question 3                new QuestionViewModel   QuestionId   1  QuestionName    Question 4                  int pageSize   3       int pageNumber    page    1        return View questions ToPagedList pageNumber  pageSize        And your Index view   model PagedList IPagedList lt ViewModel QuestionViewModel gt   using PagedList Mvc    lt link href   Content PagedList css  rel  stylesheet  type  text css    gt     lt table gt    foreach  var item in Model         lt tr gt           lt td gt               Html DisplayFor modelItem   gt  item QuestionId           lt  td gt           lt td gt               Html DisplayFor modelItem   gt  item QuestionName           lt  td gt       lt  tr gt      lt  table gt    lt br   gt   Page   Model PageCount  lt  Model PageNumber   0   Model PageNumber  of  Model PageCount  Html PagedListPager  Model  page   gt  Url Action  Index   new   page        Here is the SO link with my answer that has the step by step guide on how you can use PageList

User · Answer

For anyone who is trying to do it without modifying your ViewModels AND not loading all your records from the database   Repository      public List lt Order gt  GetOrderPage int page  int itemsPerPage  out int totalCount                List lt Order gt  orders   new List lt Order gt             using  DatabaseContext db   new DatabaseContext                          orders    from o in db Orders                       orderby o Date descending   use orderby  otherwise Skip will throw an error                       select o                         Skip itemsPerPage   page  Take itemsPerPage                         ToList                totalCount   db Orders Count     return the number of pages                   return orders   the query is now already executed  it is a subset of all the orders          Controller      public ActionResult Index int  page                int pagenumber    page    1  -1    I know what you re thinking  don t put it on 0            OrderManagement orderMan   new OrderManagement HttpContext ApplicationInstance Context           int totalCount   0          List lt Order gt  orders   orderMan GetOrderPage pagenumber  5  out totalCount           List lt OrderViewModel gt  orderViews   new List lt OrderViewModel gt             foreach Order order in orders   convert your models to some view models                        orderViews Add orderMan GenerateOrderViewModel order                        create staticPageList  defining your viewModel  current page  page size and total number of pages          IPagedList lt OrderViewModel gt  pageOrders   new StaticPagedList lt OrderViewModel gt  orderViews  pagenumber   1  5  totalCount           return View pageOrders           View   using PagedList Mvc   using PagedList     model IPagedList lt Babywatcher Core Models OrderViewModel gt          ViewBag Title    Index       lt h2 gt Index lt  h2 gt   lt div class  container-fluid  gt       lt p gt           Html ActionLink  Create New    Create        lt  p gt       if  Model Count  gt  0                   lt table class  table  gt             lt tr gt               lt th gt                   Html DisplayNameFor model   gt  model First   orderId               lt  th gt               lt  --rest of your stuff-- gt           lt  table gt             else                lt p gt No Orders yet  lt  p gt             Html PagedListPager Model  page   gt  Url Action  Index   new   page      lt  div gt    Bonus  Do above first  then perhaps use this   Since this question is about  view  models  I m going to give away a little solution for you that will not only be useful for paging  but for the rest of your application if you want to keep your entities separate  only used in the repository  and have the rest of the application deal with models  which can be used as view models     Repository  In your order repository  in my case   add a static method to convert a model   public static OrderModel ConvertToModel Order entity        if  entity    null  return null      OrderModel model   new OrderModel               ContactId   entity contactId          OrderId   entity orderId            return model      Below your repository class  add this   public static partial class Ex       public static IEnumerable lt OrderModel gt  SelectOrderModel this IEnumerable lt Order gt  source                bool includeRelations   source GetType      typeof DbQuery lt Order gt            return source Select x   gt  new OrderModel                       OrderId   x orderId                example use ConvertToModel of some other repository             BillingAddress   includeRelations   AddressRepository ConvertToModel x BillingAddress    null                example use another extension of some other repository             Shipments   includeRelations  amp  amp  x Shipments    null   x Shipments SelectShipmentModel     null                       And then in your GetOrderPage method       public IEnumerable lt OrderModel gt  GetOrderPage int page  int itemsPerPage  string searchString  string sortOrder  int  partnerId          out int totalCount                IQueryable lt Order gt  query   DbContext Orders    get queryable from db                do your filtering  sorting  paging  do not use  ToList   yet           return queryOrders SelectOrderModel   AsEnumerable              or  if you want to include relations         return queryOrders Include x   gt  x BillingAddress  ToList   SelectOrderModel              notice difference  first ToList    then SelectOrderModel            Let me explain   The static ConvertToModel method can be accessed by any other repository  as used above  I use ConvertToModel from some AddressRepository   The extension class method lets you convert an entity to a model  This can be IQueryable or any other list  collection    Now here comes the magic  If you have executed the query BEFORE calling SelectOrderModel   extension  includeRelations inside the extension will be true because the source is NOT a database query type  not an linq-to-sql IQueryable   When this is true  the extension can call other methods extensions throughout your application for converting models    Now on the other side  You can first execute the extension and then continue doing LINQ filtering  The filtering will happen in the database eventually  because you did not do a  ToList   yet  the extension is just an layer of dealing with your queries  Linq-to-sql will eventually know what filtering to apply in the Database  The inlcudeRelations will be false so that it doesn t call other c  methods that SQL doesn t understand    It looks complicated at first  extensions might be something new  but it s really useful  Eventually when you have set this up for all repositories  simply an  Include   extra will load the relations

User · Answer

The fact that you re using a view model has no bearing  The standard way of using PagedList is to store  one page of items  as a ViewBag variable  All you have to determine is what collection constitutes what you ll be paging over  You can t logically page multiple collections at the same time  so assuming you chose Instructors   ViewBag OnePageOfItems   myViewModelInstance Instructors ToPagedList pageNumber  10     Then  the rest of the standard code works as it always has

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