The `s => s.Title.Contains()` code above is a [Lambda Expression](/dotnet/csharp/programming-guide/statements-expressions-operators/lambda-expressions). Lambdas are used in method-based [LINQ](/dotnet/standard/using-linq) queries as arguments to standard query operator methods such as the [Where](/dotnet/api/system.linq.enumerable.where) method or `Contains` (used in the code above). LINQ queries are not executed when they're defined or when they're modified by calling a method such as `Where`, `Contains`, or `OrderBy`. Rather, query execution is deferred. That means that the evaluation of an expression is delayed until its realized value is actually iterated over or the `ToListAsync` method is called. For more information about deferred query execution, see [Query Execution](/dotnet/framework/data/adonet/ef/language-reference/query-execution).
Note: The [Contains](/dotnet/api/system.data.objects.dataclasses.entitycollection-1.contains) method is run on the database, not in the c# code shown above. The case sensitivity on the query depends on the database and the collation. On SQL Server, [Contains](/dotnet/api/system.data.objects.dataclasses.entitycollection-1.contains) maps to [SQL LIKE](/sql/t-sql/language-elements/like-transact-sql), which is case insensitive. In SQLite, with the default collation, it's case sensitive.
If you change the signature of the `Index` method to have a parameter named `id`, the `id` parameter will match the optional `{id}` placeholder for the default routes set in *Startup.cs*.
You can now pass the search title as route data (a URL segment) instead of as a query string value.
However, you can't expect users to modify the URL every time they want to search for a movie. So now you'll add UI elements to help them filter movies. If you changed the signature of the `Index` method to test how to pass the route-bound `ID` parameter, change it back so that it takes a parameter named `searchString`:
The HTML `<form>` tag uses the [Form Tag Helper](xref:mvc/views/working-with-forms), so when you submit the form, the filter string is posted to the `Index` action of the movies controller. Save your changes and then test the filter.
There's no `[HttpPost]` overload of the `Index` method as you might expect. You don't need it, because the method isn't changing the state of the app, just filtering data.
You could add the following `[HttpPost] Index` method.
The `notUsed` parameter is used to create an overload for the `Index` method. We'll talk about that later in the tutorial.
If you add this method, the action invoker would match the `[HttpPost] Index` method, and the `[HttpPost] Index` method would run as shown in the image below.
However, even if you add this `[HttpPost]` version of the `Index` method, there's a limitation in how this has all been implemented. Imagine that you want to bookmark a particular search or you want to send a link to friends that they can click in order to see the same filtered list of movies. Notice that the URL for the HTTP POST request is the same as the URL for the GET request (localhost:{PORT}/Movies/Index) -- there's no search information in the URL. The search string information is sent to the server as a [form field value](https://developer.mozilla.org/docs/Learn/HTML/Forms/Sending_and_retrieving_form_data). You can verify that with the browser Developer tools or the excellent [Fiddler tool](https://www.telerik.com/fiddler). The image below shows the Chrome browser Developer tools:
You can see the search parameter and [XSRF](xref:security/anti-request-forgery) token in the request body. Note, as mentioned in the previous tutorial, the [Form Tag Helper](xref:mvc/views/working-with-forms) generates an [XSRF](xref:security/anti-request-forgery) anti-forgery token. We're not modifying data, so we don't need to validate the token in the controller method.
Because the search parameter is in the request body and not the URL, you can't capture that search information to bookmark or share with others. Fix this by specifying the request should be `HTTP GET` found in the *Views/Movies/Index.cshtml* file.
Now when you submit a search, the URL contains the search query string. Searching will also go to the `HttpGet Index` action method, even if you have a `HttpPost Index` method.
The following markup shows the change to the `form` tag:
In the preceding code, the `DisplayNameFor` HTML Helper inspects the `Title` property referenced in the lambda expression to determine the display name. Since the lambda expression is inspected rather than evaluated, you don't receive an access violation when `model`, `model.Movies`, or `model.Movies[0]` are `null` or empty. When the lambda expression is evaluated (for example, `@Html.DisplayFor(modelItem => item.Title)`), the model's property values are evaluated.
