However, the above code won’t be enough to prevent the insertion of an invalid book into the data store. Here is the code for the book insertion view model post the addition of the data validation attributes: public class InsertBookViewModel Here is how the code for the book insertion form will look like That is achieved using the HTML helper, ValidationMessageFor. Meanwhile, our simple form of inserting books will have to be extended to include placeholders where the validation exception messages are going to be displayed. In such cases, the validation will have to be part of the domain logic itself. Unfortunately, the same won’t be enough for creating client-side validation or for forms where complex validations are required. For instance, it might be perfect for validating things like matching the password and so on. The same code post addition of data annotations will look like the following: public class InsertBookViewModelĪt this point, it is important to keep in mind that the above data annotation will only allow for the basic form of data validation in the backend. The view includes fields for entering the Title, Author, Price, and Number of pages of the book. For convenience, we consider here a simple application that is used to insert a book. Here is an example code to demonstrate the above concept. Example of Data Annotations in ASP.NET Core This applies to those fields where the user is required to enter data such as an email address, social security number, phone numbers, zip codes, and so on.Ĭompare: this is applicable for those fields where you need to compare two strings, like say for password validation.ĭisplay: Will allow you to set the label text.ĭataType: this lets you determine how the output controls get rendered in the browser, like say for a password or an email. Regular expression: the user must enter a value that must match a given format or a regular expression. Range: the user has to enter a numeric value that falls within the range as defined here. Required: the particular field with this data annotation can’t be left empty. MinLength and MaxLength: the length of the string that the user enters must be within the minimum and maximum limits as defined here. Some of the most commonly used data annotations Data annotations are specified inside square brackets with the option to include a single annotation in a code line or have a bunch of them separated by a comma in a single line. You can use back-end modeling attributes to set field type, mask, and such.ĭata annotations can be found in the Namespace. For instance, using the front-end validation attribute, you can specify if a particular field must be filled up, set min and max limits, and so on.įront-end display attributes: This will let you specify the manner the properties from your Model gets displayed on the screen for the user to see.īack-end modeling attributes: This can be used to set table limitations as well as the relationships between classes. Those include:įront-end validation attribute: This enables you to validate the data that the users would be required to input. There are three areas where you might be needed to use data annotations in your application. The data again can be of any type, such as text, integer, double, or boolean. Similarly, if there is an age field, you will be able to set the minimum and maximum age that the user can input for the value to be considered valid. Example of Data Annotations in ASP.NET Coreįor instance, if it is a name field, you can specify it to accept only characters and the maximum number of characters that it can accept.Some of the most commonly used data annotations.
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