Creating MVC Application & Perform CRUD operations using LINQ to SQL: Part 2

When we open MyDB.designer.cs, we get the MyDBDataContext class. This class holds database user table information in the form of classes and properties. For every column of the table, properties are created in the class, and we can use these properties to get/set values from/in database.

4. Perform CRUD operations in MVC application using LINQ to SQL

We now have a database, a context class to communicate with the database and a MVC application to perform CRUD operations in the database using the context class.

Step 1 Read

• Go to Index Action, make an instance of the context class. We can get all the table and column names in that context's instance.

• Make a query to display all the records on the Index view.

• Populate the User Model that we created earlier, and it to the Index view (Index View will be of a List type Item template).

When we run the application, we get an empty list, in other words we don't have records in the database.

Step 2 Create

• First write code for creating a user, for the first time for the Get Action of create, always an empty view will be returned.
  
  
  

• When we post some data on the click of the submit of Create, we need to make a data entry in the table for creating a new user.

• When the form is posted, it fires a Post Action of Create with the already bound User model properties to view fields, we'll retrieve these model properties and make an instance of the context class to populate the context User and submit to the database.
  
  
  

• Redirect action to Index, and now a record will be shown on the Index View. We successfully created a user.
  
  
  

• In the database:
  
  

Step 3 Update

Step 4 Delete

Now we are smart enough to perform update and delete by ourself, this I leave for the reader's understanding capabilities, the following are the screens for Update and Delete.

Edit Code:
Get:

Post:

Get Action View of Edit:

Edited few fields:

Update reflected in database:

Code to show details of a particular user :

Details Screen:

Note: a Details Action does not have a POST, since nothing is posted to the controller.

Likewise for Delete:
Screen:

Back to List after Delete:

In database after delete:

Yes, all the CRUD operations are done. Now we understand MVC.



There are a few basic scenarios that I want to discuss before finishing with the First Part, like ing data from the Controller to Views, between Controllers and so on and about Model validation.

5. Understand ViewData, ViewBag and TempData

I wanted to use this topic since there is so much confusion regarding these three players.

MVC provides us ViewData, VieBag and TempData for ing data from a controller and view and in future requests as well. ViewData and ViewBag are similar to some extent but TempData performs additional roles. Let's get the key points of these three players:

ViewBag & ViewData

I have written sample test code in the same application that we are following from the beginning,

• Populate ViewData and ViewBag on Index action of My Controller.
  
  
  

• Code in View to fetch ViewData/ViewBag.
  
  
  

• When run the application, we get one screen.
  
  
  

The following are the roles and similarities between ViewData and ViewBag:

• Maintains data when moving from controller to view.

• es data from controller to respective view.

• Their value becomes null when any redirection occurs , because their role is to provide a way to communicate between controllers and views. It's a communication mechanism within the server call.

Differences between ViewData and ViewBag (taken from a blog)

• ViewData is a dictionary of objects that is derived from the ViewDataDictionary class and accessible using strings as keys.

• ViewBag is a dynamic property that takes advantage of the new dynamic features in C# 4.0.

• ViewData requires typecasting for complex data types and check for null values to avoid errors.

• ViewBag doesn't require typecasting for complex data types.

TempData

TempData is a dictionary derived from the TempDataDictionary class and stored in a short-lived session. It is a string key and object value.

It maintains the information for the time of an HTTP Request. This mean only from one page to another. It helps to maintain data when we move from one controller to another controller or from one action to another action. In other words, when we redirect, "Tempdata" helps to maintain data between those redirects. It internally uses session variables. Temp data is used during the current and subsequent request only, in other words it is used when we are sure that the next request will be redirecting to the next view. It requires typecasting for complex data types and checks for null values to avoid errors. Generally it is used to store only one-time messages, like error messages and validation messages.

I added a TempData in Edit Action as:

And when View redirected to Index Action:



In other words I get the TempData value across Actions.

6. Model Validation

We can have many methods for implementing validation in our Web Application Client Side, Server Side and so on.

But MVC provides us a feature with which we can annotate our Model for validation by writing just one or two lines of code.

Go to the Model class User.cs, add [Required(ErrorMessage = "FirstName is required")] on the top of FirstName property as in:

Now when we run the application, and try to Edit/Create a user without specifying FirstName, we get:

Surprised? Yes the model validates itself with these annotations, there are many more validators like the required field one that I used.

Do not forget to include "using System.ComponentModel.DataAnnotations;" for the namespace when using Model Validation. This is the namespace that holds classes used for validation.

Conclusion

Now that we understand what MVC is, how to implement it, its advantages and, CRUD operations in MVC. Future parts of the tutorial will be focusing on more advanced topics, like EntityFramework, Repository Pattern, Unit Of Work Pattern and Code First Approach.