ASP NET MVC 5 中的数据注释和HTML辅助器类

Table of Contents

1. Introduction
2. Lab 8: Data, Annotations, and Helper Classes
   1. Videos on Attributes, Data Annotations, and Regular Expression
   2. Understanding Data Annotations
   3. Validations with Data Annotations
   4. Implementing Required Attribute
   5. Implementing STRING Length Attribute
   6. Implementing Regular Expression Attribute
   7. Running Validations on the Server Side
   8. Displaying Error Messages
   9. Improving User Friendliness
3. Client-side Validations with jQuery
   1. Introduction to jQuery
   2. Including jQuery Files
   3. Creating UI Elements with HTML Helper Class
   4. Emitting Client-side Validations
4. Conclusion

Lab 8: Data, Annotations, and Helper Classes

In this lab, we will explore the concepts of data annotations and helper classes in MVC. Before we begin, it is recommended to watch three prerequisite videos on attributes, data annotations, and regular expressions from the dot net fundamentals section.

Videos on Attributes, Data Annotations, and Regular Expression

To better understand data annotations and their usage in MVC, we highly recommend watching three videos: one on attributes, another on data annotations, and the third one on regular expressions. These videos serve as a foundation for understanding the concepts discussed in this lab.

Understanding Data Annotations

Data annotations are attributes that allow us to perform validations in MVC. These attributes can be applied to model classes and help ensure data integrity. In this lab, we will be working with the same project used in Lab 5, where we discussed model binders.

Validations with Data Annotations

To demonstrate how data annotations work, we will be working with a simple customer model. The first validation we will implement is to ensure that the customer name and customer code are not empty. This can be achieved using the Required data annotation.

Implementing Required Attribute

To ensure that the customer name and customer code are not empty, we will decorate the corresponding properties in the customer model with the Required attribute. This attribute can be imported by adding the System.ComponentModel.DataAnnotations namespace. By using the Required attribute, we can easily perform validations in MVC.

Implementing String Length Attribute

In addition to the Required attribute, we can also enforce a maximum character limit on the customer name. To achieve this, we will use the StringLength attribute. By specifying the maximum length of the customer name, we can ensure that it does not exceed the specified limit.

Implementing Regular Expression Attribute

The third requirement is to validate the format of the customer code. The customer code should follow a specific pattern, such as "abc1234" or "pqr43457". To achieve this, we will use the RegularExpression attribute. Regular expressions allow us to specify a pattern that the customer code should match. In the case of our example, the pattern will be three letters followed by four numbers.

Running Validations on the Server Side

When does the validation occur on the customer object? There are two ways validations can run. We can manually run the validations using the Validator class, or we can let the validations run automatically when the objects are filled in the customer via post or get methods. In our case, as soon as the user submits the form, the validations are triggered and any errors are sent to the ModelState class.

Displaying Error Messages

To display the error messages generated by the validations, we need to modify the enter customer screen. We can use the Html.ValidationSummary method to display a summary of all the error messages. Additionally, we can use the Html.ValidationMessageFor method to display individual error messages next to the respective input fields.

Improving User Friendliness

While we have implemented data annotations and are displaying error messages, there is room for improvement in terms of user-friendliness. Currently, when the user submits the form and encounters validation errors, the entered values are not persisted. To enhance the user experience, we need to pass the customer object back to the enter customer screen so that the user can see the previously entered values.

Client-side Validations with jQuery

To further optimize the performance, we can enable client-side validations using jQuery. jQuery is a JavaScript library that simplifies JavaScript coding. By incorporating jQuery into our project, we can leverage client-side computing power and improve performance.

Introduction to jQuery

Before we proceed with client-side validations, it is recommended to familiarize yourself with jQuery. jQuery is a library that makes JavaScript coding simpler. It offers a range of features and functionalities that can enhance client-side interactions.

Including jQuery Files

To enable client-side validations, we need to include three jQuery files in a specific sequence. The first file is the main jQuery file, followed by the jquery.validate.js file, and the jquery.validate.unobtrusive.js file. These files play a crucial role in emitting validators and organizing JavaScript and elements.

Creating UI Elements with HTML Helper Class

To simplify the creation of HTML UI elements, we can utilize the HTML helper class. This class offers various methods for generating UI elements such as text boxes, text areas, checkboxes, and radio buttons. By using these helper methods, we can generate the HTML elements and attach them to the model properties.

Emitting Client-side Validations

Once the necessary jQuery files are included and the UI elements are created, we can emit client-side validations using the HTML helper class. By specifying the appropriate validation attributes on the model properties and using the HTML helpers, the respective client-side validations will be triggered when the user interacts with the form.

Conclusion

In this lab, we explored the concepts of data annotations, helper classes, and client-side validations using jQuery in MVC. We learned how to implement various validations on the server side using data annotations and display error messages to the user. Additionally, by enabling client-side validations, we improved performance and enhanced the user experience. By combining data annotations, helper classes, and jQuery, we can Create robust and user-friendly applications in MVC.

Frequently Asked Questions

Q: Can I use data annotations for custom validations? A: Yes, data annotations can be used for custom validations by creating custom validation attributes and applying them to the appropriate model properties.

Q: Can client-side validations replace server-side validations? A: While client-side validations can enhance the user experience and improve performance, it is still recommended to perform server-side validations as a fallback. Client-side validations can be disabled or bypassed, so server-side validations add an extra layer of security.

Q: Is jQuery required for client-side validations in MVC? A: Yes, jQuery is essential for enabling client-side validations in MVC. It provides the necessary JavaScript functionalities and simplifies the process of emitting client-side validations.

Q: What if a user disables JavaScript in their browser? A: If a user disables JavaScript, client-side validations will not be triggered. In such cases, it is crucial to have server-side validations to ensure data integrity and security.

Q: Can I customize the error messages displayed for each validation? A: Yes, you can customize the error messages for each validation by specifying them as parameters in the data annotation attributes.