Model Validation in ASP.NET Web API

In our ASP.NET Web API article series, we already have created an application that is performing all CRUD (Create, Retrieve, Update, Delete) operations using Web API. Here we will take the same domain model class i.e. “Student.cs” and apply validation on it using data annotation method. In order to better understand with more validation rules, I modified it a bit. So, here is our Model class:

We have applied some validation to our model class properties in the same manner as a database table’s fields have associated validation rules. We have applied the attributes to model properties using System.ComponentModel.DataAnnotations namespace.

Our Model class i.e. Student has following validation rules.

• StudentID value must be between 1 and 500.
• FirstName is also required with maximum length of 10.
• LastName has no associated rule.

We will check the validity of Model against the defined validation rules in controller class i.e. StudentController.

Now, when the client will send a POST request in JSON format, its being converted to Student object instance and that instance will be validated against the rules defined in Model class. In above code sample, line # 5, Student instance state is validated and accordingly response is generated.

JSON representation 1 & 2 will return with the message “Bad Request….Request is Invalid….” because:

1. StudentID value not between the defined validation range (1 to 500).
2. FirstName maximum defined length exceeded.

JSON representation 3 is valid and response with status code of 200 will be returned.
Data annotation technique for Model validation is really helpful because it validates data before involving in any further processing. But there are some limitations associated with this approach i.e. Under-Posting and Over-Posting. Follow the post for Limitations to Model Validation in ASP.NET Web API.