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Dynamic Model Binding in ASP.NET Core Web API

Introduction

Dynamic model binding in ASP.NET Core Web API allows you to bind incoming HTTP request data to a dynamic object, which can be useful when you don't know the structure of the incoming data in advance. This approach can be handy for scenarios like working with JSON objects where the structure may vary.

How to achieve dynamic model binding in ASP.NET Core?

Here's a step-by-step guide on how to achieve dynamic model binding in ASP.NET Core Web API:

Step 1. Create a new ASP.NET Core Web API project or open an existing one.

Step 2. Create a custom model binder for dynamic objects. You can do this by implementing the IModelBinder interface. Here's a basic example of a dynamic model binder:

using System;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using System.Text.Json;
using System.Threading.Tasks;

public class DynamicModelBinder : IModelBinder
{
    public Task BindModelAsync(ModelBindingContext bindingContext)
    {
        if (bindingContext == null)
        {
            throw new ArgumentNullException(nameof(bindingContext));
        }

        var valueProviderResult = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
        if (valueProviderResult == ValueProviderResult.None)
        {
            return Task.CompletedTask;
        }

        try
        {
            var stringValue = valueProviderResult.FirstValue;
            var result = JsonSerializer.Deserialize<ExpandoObject>(stringValue);
            bindingContext.Result = ModelBindingResult.Success(result);
        }
        catch
        {
            bindingContext.ModelState.TryAddModelError(bindingContext.ModelName, "Invalid JSON");
        }

        return Task.CompletedTask;
    }
}

Step 3. Register the custom model binder you're Startup.cs within the ConfigureServices method:

services.AddMvc(options =>
{
    options.ModelBinderProviders.Insert(0, new BinderTypeModelBinder(typeof(DynamicModelBinder)));
});

Step 4. Create a controller action that accepts a dynamic object as a parameter. You can then use this dynamic object to access the incoming data.

[HttpPost("dynamic")]
public IActionResult PostDynamic([ModelBinder(typeof(DynamicModelBinder))] dynamic data)
{
    // Use the dynamic 'data' object as needed
    // Example: dynamicValue = data.SomeProperty;
    return Ok(data);
}

Step 5. Make a POST request to the controller action with a JSON body. The JSON object's structure can vary, and the dynamic model binder will bind it to the dynamic parameter.

For example, if you send a POST request with a JSON body like this:

{
    "Name": "Gajendra",
    "Age": 30
}

The data parameter in the controller action will contain the dynamic object with properties "Name" and "Age."

Note. Please note that using dynamic objects in this way can make your code less type-safe and can be challenging to work with in larger projects. It's often a better practice to define strong types for your API endpoints when possible. Dynamic model binding should be used sparingly, primarily when you have no control over the structure of incoming data.


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