Question

We are having an issue with Nancy’s default model binder. Given the below…

public class Foo
{
    public Foo()
    {
    }

    public string Name { get; set; }

    public Bar Bar { get; set; }
}

public class Bar
{
    public string Name { get; set; }
}

with elements like…

<input type="text" value="Name" />
<input type="text" value="Bar.Name" />

With the default model binder used like so..

var foo = this.Bind<Foo>();

This correctly binds Foo.Name but fails to bind Foo.Bar.Name

Is there a way to enable this kind of binding with the default binder or do we need to roll our own? If so are there any good examples?

Answer 1

Why not try this. I’m fairly sure the recursion could be optimised, and that something will come up where it doesn’t work, and that it could be put somewhere cleverer than a IModelBinder, but it basically does what you want.

/// <summary>
/// Sample model binder that manually binds customer models
/// </summary>
public class CustomModelBinder : IModelBinder
{
    /// <summary>
    /// Bind to the given model type
    /// </summary>
    /// <param name="context">Current context</param>
    /// <param name="modelType">Model type to bind to</param>
    /// <param name="blackList">Blacklisted property names</param>
    /// <returns>Bound model</returns>
    public object Bind(NancyContext context, Type modelType, params string[] blackList)
    {
        var parentObject = Activator.CreateInstance(modelType);

        foreach (var key in context.Request.Form)
        {
            var value = context.Request.Form[key];
            this.SetObjectValue(parentObject, modelType, key, value);
        }

        return parentObject;
    }

    /// <summary>
    /// Sets the object value.
    /// </summary>
    /// <param name="instance">The instance.</param>
    /// <param name="type">The type.</param>
    /// <param name="key">Name of the property.</param>
    /// <param name="propertyValue">The property value.</param>
    private void SetObjectValue(object instance, Type type, string key, string propertyValue)
    {
        if (key.Contains("."))
        {
            this.SetObjectValueDeep(instance, type, key, propertyValue);
        }

        PropertyInfo propertyInfo = type.GetProperty(key);
        if (propertyInfo == null)
        {
            return;
        }

        propertyInfo.SetValue(instance, Convert.ChangeType(propertyValue, propertyInfo.PropertyType), null);
    }

    /// <summary>
    /// Sets the object value derp.
    /// </summary>
    /// <param name="instance">The instance.</param>
    /// <param name="type">The type.</param>
    /// <param name="key">The key.</param>
    /// <param name="propertyValue">The property value.</param>
    private void SetObjectValueDeep(object instance, Type type, string key, string propertyValue)
    {
        var propList = key.Split('.').ToList();

        PropertyInfo propertyInfo = type.GetProperty(propList.First());
        if (propertyInfo == null)
        {
            return;
        }

        var childObject = propertyInfo.GetValue(instance, null);

        if (childObject == null)
        {
            childObject = Activator.CreateInstance(propertyInfo.PropertyType);
            propertyInfo.SetValue(instance, childObject, null);
        }

        propList.RemoveAt(0);

        var newKey = propList.Aggregate(string.Empty, (current, prop) => current + (prop + ".")).TrimEnd('.');

        if (newKey.Contains("."))
        {
            this.SetObjectValueDeep(childObject, childObject.GetType(), newKey, propertyValue);
        }
        else
        {
            this.SetObjectValue(childObject, childObject.GetType(), newKey, propertyValue);
        }
    }

    /// <summary>
    /// Determines whether this instance can bind the specified model type.
    /// </summary>
    /// <param name="modelType">Type of the model.</param>
    /// <returns>
    ///   <c>true</c> if this instance can bind the specified model type; otherwise, <c>false</c>.
    /// </returns>
    public bool CanBind(Type modelType)
    {
        return true;
    }
}