ASP.NET Core’s default model binder is quite versatile, it might not always meet your specific needs. This is where custom model binders step in, allowing you to precisely define how data is extracted from incoming requests and mapped onto your model properties. Purpose Flexibility: Handle complex or custom data formats that the default model binder doesn’t understand. Custom Logic: Implement specific business rules or data transformations during binding. Complete Control: Take full control over the binding process, from parsing the raw data to populating your model object.
Implementing IModelBinder To create a custom model binder, you implement the IModelBinder interface: public interface IModelBinder { Task BindModelAsync(ModelBindingContext bindingContext); } The core of your custom logic resides in the BindModelAsync method, where you: Retrieve raw data from the bindingContext.ValueProvider. Parse and validate the data according to your requirements. Create an instance of your model class and populate its properties. Set the bindingContext.Result to ModelBindingResult.Success(yourModelInstance).
Code // PersonModelBinder.cs public class PersonModelBinder : IModelBinder { public Task BindModelAsync(ModelBindingContext bindingContext) { Person person = new Person();
// … (Logic to extract and populate properties from the ValueProvider) …
bindingContext.Result = ModelBindingResult.Success(person); return Task.CompletedTask; } } In this example, PersonModelBinder: Creates a new Person object. Extracts values for different properties (e.g., PersonName, Email, Phone) from the ValueProvider (which can access form data, query string, route data, etc.). Performs some basic transformations (concatenating FirstName and LastName). Sets the model binding result to indicate success and return the populated Person object.
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