Sorting, Filtering, and Paging with the Entity Framework in an ASP.NET MVC Application | Microsoft Docs
The Contoso University sample web application demonstrates how to create ASP.NET MVC 5 applications using the Entity Framework 6 Code First and Visual Studio...
Sorting, filtering, and paging with the Entity Framework in an ASP.NET MVC application
by Tom Dykstra
The Contoso University sample web application demonstrates how to create ASP.NET MVC 5 applications using the Entity Framework 6 Code First and Visual Studio. For information about the tutorial series, see the first tutorial in the series.
In the previous tutorial, you implemented a set of web pages for basic CRUD operations for
Student entities. In this tutorial you'll add sorting, filtering, and paging functionality to the Students Index page. You'll also create a page that does simple grouping.
The following illustration shows what the page will look like when you're done. The column headings are links that the user can click to sort by that column. Clicking a column heading repeatedly toggles between ascending and descending sort order.
Add column sort links to the Students index page
To add sorting to the Student Index page, you'll change the
Index method of the
Student controller and add code to the
Student Index view.
Add sorting functionality to the Index method
In Controllers\StudentController.cs, replace the
Indexmethod with the following code:
This code receives a
sortOrder parameter from the query string in the URL. The query string value is provided by ASP.NET MVC as a parameter to the action method. The parameter is a string that's either "Name" or "Date", optionally followed by an underscore and the string "desc" to specify descending order. The default sort order is ascending.
The first time the Index page is requested, there's no query string. The students are displayed in ascending order by
LastName, which is the default as established by the fall-through case in the
switch statement. When the user clicks a column heading hyperlink, the appropriate
sortOrder value is provided in the query string.
ViewBag variables are used so that the view can configure the column heading hyperlinks with the appropriate query string values:
These are ternary statements. The first one specifies that if the
sortOrder parameter is null or empty,
ViewBag.NameSortParm should be set to "name_desc"; otherwise, it should be set to an empty string. These two statements enable the view to set the column heading hyperlinks as follows:
|Current sort order||Last Name Hyperlink||Date Hyperlink|
|Last Name ascending||descending||ascending|
|Last Name descending||ascending||ascending|
The method uses LINQ to Entities to specify the column to sort by. The code creates an xref:System.Linq.IQueryable%601 variable before the
switch statement, modifies it in the
switch statement, and calls the
ToList method after the
switch statement. When you create and modify
IQueryable variables, no query is sent to the database. The query is not executed until you convert the
IQueryable object into a collection by calling a method such as
ToList. Therefore, this code results in a single query that is not executed until the
return View statement.
As an alternative to writing different LINQ statements for each sort order, you can dynamically create a LINQ statement. For information about dynamic LINQ, see Dynamic LINQ.
Add column heading hyperlinks to the Student index view
In Views\Student\Index.cshtml, replace the
<th>elements for the heading row with the highlighted code:
This code uses the information in the
ViewBagproperties to set up hyperlinks with the appropriate query string values.
Run the page and click the Last Name and Enrollment Date column headings to verify that sorting works.
After you click the Last Name heading, students are displayed in descending last name order.
Add a search box to the Students index page
To add filtering to the Students index page, you'll add a text box and a submit button to the view and make corresponding changes in the
Index method. The text box lets you enter a string to search for in the first name and last name fields.
Add filtering functionality to the Index method
In Controllers\StudentController.cs, replace the
Indexmethod with the following code (the changes are highlighted):
The code adds a
searchString parameter to the
Index method. The search string value is received from a text box that you'll add to the Index view. It also adds a
where clause to the LINQ statement that selects only students whose first name or last name contains the search string. The statement that adds the xref:System.Linq.Queryable.Where%2A clause executes only if there's a value to search for.
[!NOTE] In many cases you can call the same method either on an Entity Framework entity set or as an extension method on an in-memory collection. The results are normally the same but in some cases may be different.
For example, the .NET Framework implementation of the
Containsmethod returns all rows when you pass an empty string to it, but the Entity Framework provider for SQL Server Compact 4.0 returns zero rows for empty strings. Therefore the code in the example (putting the
Wherestatement inside an
ifstatement) makes sure that you get the same results for all versions of SQL Server. Also, the .NET Framework implementation of the
Containsmethod performs a case-sensitive comparison by default, but Entity Framework SQL Server providers perform case-insensitive comparisons by default. Therefore, calling the
ToUppermethod to make the test explicitly case-insensitive ensures that results do not change when you change the code later to use a repository, which will return an
IEnumerablecollection instead of an
IQueryableobject. (When you call the
Containsmethod on an
IEnumerablecollection, you get the .NET Framework implementation; when you call it on an
IQueryableobject, you get the database provider implementation.)
Null handling may also be different for different database providers or when you use an
IQueryableobject compared to when you use an
IEnumerablecollection. For example, in some scenarios a
Wherecondition such as
table.Column != 0may not return columns that have
nullas the value. For more information, see Incorrect handling of null variables in 'where' clause.
Add a search box to the Student index view
In Views\Student\Index.cshtml, add the highlighted code immediately before the opening
tabletag in order to create a caption, a text box, and a Search button.
Run the page, enter a search string, and click Search to verify that filtering is working.
Notice the URL doesn't contain the "an" search string, which means that if you bookmark this page, you won't get the filtered list when you use the bookmark. This applies also to the column sort links, as they will sort the whole list. You'll change the Search button to use query strings for filter criteria later in the tutorial.
Add paging to the Students index page
To add paging to the Students index page, you'll start by installing the PagedList.Mvc NuGet package. Then you'll make additional changes in the
Index method and add paging links to the
Index view. PagedList.Mvc is one of many good paging and sorting packages for ASP.NET MVC, and its use here is intended only as an example, not as a recommendation for it over other options. The following illustration shows the paging links.
Install the PagedList.MVC NuGet package
The NuGet PagedList.Mvc package automatically installs the PagedList package as a dependency. The PagedList package installs a
PagedList collection type and extension methods for
IEnumerable collections. The extension methods create a single page of data in a
PagedList collection out of your
IEnumerable, and the
PagedList collection provides several properties and methods that facilitate paging. The PagedList.Mvc package installs a paging helper that displays the paging buttons.
From the Tools menu, select NuGet Package Manager and then Package Manager Console.
In the Package Manager Console window, make sure the Package source is nuget.org and the Default project is ContosoUniversity, and then enter the following command:
Build the project.
Add paging functionality to the Index method
In Controllers\StudentController.cs, add a
usingstatement for the
Indexmethod with the following code:
This code adds a
pageparameter, a current sort order parameter, and a current filter parameter to the method signature:
The first time the page is displayed, or if the user hasn't clicked a paging or sorting link, all the parameters are null. If a paging link is clicked, the
pagevariable contains the page number to display.
ViewBagproperty provides the view with the current sort order, because this must be included in the paging links in order to keep the sort order the same while paging:
ViewBag.CurrentFilter, provides the view with the current filter string. This value must be included in the paging links in order to maintain the filter settings during paging, and it must be restored to the text box when the page is redisplayed. If the search string is changed during paging, the page has to be reset to 1, because the new filter can result in different data to display. The search string is changed when a value is entered in the text box and the submit button is pressed. In that case, the
searchStringparameter is not null.
At the end of the method, the
ToPagedListextension method on the students
IQueryableobject converts the student query to a single page of students in a collection type that supports paging. That single page of students is then passed to the view:
ToPagedListmethod takes a page number. The two question marks represent the null-coalescing operator. The null-coalescing operator defines a default value for a nullable type; the expression
(page ?? 1)means return the value of
pageif it has a value, or return 1 if
Add paging links to the Student index view
In Views\Student\Index.cshtml, replace the existing code with the following code. The changes are highlighted.
@modelstatement at the top of the page specifies that the view now gets a
PagedListobject instead of a
PagedList.Mvcgives access to the MVC helper for the paging buttons.
The default BeginForm submits form data with a POST, which means that parameters are passed in the HTTP message body and not in the URL as query strings. When you specify HTTP GET, the form data is passed in the URL as query strings, which enables users to bookmark the URL. The W3C guidelines for the use of HTTP GET recommend that you should use GET when the action does not result in an update.
The text box is initialized with the current search string so when you click a new page you can see the current search string.
The column header links use the query string to pass the current search string to the controller so that the user can sort within filter results:
The current page and total number of pages are displayed.
If there are no pages to display, "Page 0 of 0" is shown. (In that case the page number is greater than the page count because
Model.PageNumberis 1, and
The paging buttons are displayed by the
PagedListPagerhelper provides a number of options that you can customize, including URLs and styling. For more information, see TroyGoode / PagedList on the GitHub site.
Run the page.
Click the paging links in different sort orders to make sure paging works. Then enter a search string and try paging again to verify that paging also works correctly with sorting and filtering.
Create an About page that shows Student statistics
For the Contoso University website's About page, you'll display how many students have enrolled for each enrollment date. This requires grouping and simple calculations on the groups. To accomplish this, you'll do the following:
- Create a view model class for the data that you need to pass to the view.
- Modify the
Aboutmethod in the
- Modify the
Create the View Model
Create a ViewModels folder in the project folder. In that folder, add a class file EnrollmentDateGroup.cs and replace the template code with the following code:
Modify the Home Controller
In HomeController.cs, add the following
usingstatements at the top of the file:
Add a class variable for the database context immediately after the opening curly brace for the class:
Aboutmethod with the following code:
The LINQ statement groups the student entities by enrollment date, calculates the number of entities in each group, and stores the results in a collection of
EnrollmentDateGroupview model objects.
Modify the About View
Replace the code in the Views\Home\About.cshtml file with the following code:
Run the app and click the About link.
The count of students for each enrollment date displays in a table.
In this tutorial you've seen how to create a data model and implement basic CRUD, sorting, filtering, paging, and grouping functionality. In the next tutorial, you'll begin looking at more advanced topics by expanding the data model.
Please leave feedback on how you liked this tutorial and what we could improve.
Links to other Entity Framework resources can be found in ASP.NET Data Access - Recommended Resources.