Solving ASP.NET Web Service Proxy Class Type Conversion Issues: A Practical Guide

When working with ASP.NET web services, developers often encounter a common problem related to type conversion between the returned data from the web service and their own business objects. If you’re a newcomer to the ASP.NET realm, understanding how these components interact can be a daunting challenge. Let’s break down this problem and explore effective solutions.

Understanding the Problem

Imagine you have a standard business object called Contact within the Business namespace. You write a web service to retrieve a Contact’s information from a database and send that data back to a client application. The client application can invoke methods on that service to access the Contact data.

Now, picture this scenario:

1. Business Object: The business object is created, Contact exists in the Business namespace.
2. Web Service: A web service is developed which includes a method GetContact that returns a MyWebService.Contact object.
3. Client Application: The client application calls this web service to get the Contact data and is expected to use a utility method like Utils.BuyContactNewHat(Contact).

The Issue

Here lies the problem: when the client application tries to use the Contact data returned by the web service, it gets a MyWebService.Contact object, which doesn’t match the expected type of Business.Contact. The code will throw an error upon attempting to call the utility method, indicating a type mismatch:

Contact c = MyWebService.GetContact("Rob");
Utils.BuyContactNewHat(c); // Error Here

This occurs because you are interfacing with the proxy class generated by the WSDL when accessing the web service, which creates the discrepancy in types.

Effective Solutions

Navigating this type mismatch can be challenging, but there are strategies to simplify the process:

1. Property Copying

The recommended approach is to manually copy the values from the MyWebService.Contact object to your Business.Contact object. This requires a method to map relevant properties across the two classes, effectively creating an instance of Business.Contact with the data retrieved.

Here’s an example method for copying values:

public Business.Contact ConvertToBusinessContact(MyWebService.Contact webServiceContact)
{
    return new Business.Contact
    {
        Name = webServiceContact.Name,
        Email = webServiceContact.Email,
        Phone = webServiceContact.Phone
        // Continue mapping additional properties here
    };
}

2. Utilizing Reflection

For a more generic solution, you could implement a converter class that leverages reflection to copy properties based on their names and types. This allows you to avoid hardcoding mappings, though it may introduce overhead in performance due to reflection usage. Here’s a simplified version for reference:

public static TTarget Convert<TSource, TTarget>(TSource source)
    where TTarget : new()
{
    var target = new TTarget();
    foreach (var sourceProp in typeof(TSource).GetProperties())
    {
        var targetProp = typeof(TTarget).GetProperty(sourceProp.Name);
        if (targetProp != null && targetProp.CanWrite)
        {
            targetProp.SetValue(target, sourceProp.GetValue(source));
        }
    }
    return target;
}

3. Explore Alternatives

If you’re open to alternatives, consider whether web services are necessary for your design. Options like .NET remoting or binary serialization may offer more streamlined object passing. However, if you’re committed to using web services, then property copying remains paramount.

Conclusion

Understanding how to interface with web services and handle object type conversions is crucial for any ASP.NET developer. With a little setup, you can efficiently navigate proxy class discrepancies. Whether you choose to copy properties manually or implement a more generic solution through reflection, the key is to ensure your business logic remains intact and functional.

As you continue your journey in ASP.NET, remember that encountering these types of challenges is part of the learning process. By utilizing the methods outlined in this post, you’ll be better equipped to handle similar situations in the future.