Is POSTing a Dictionary to an .NET MVC action possible?

Question

I have a form which contains a series of fields like:

<input type="text" name="User[123]" value="Alice" />
<input type="text" name="User[456]" value="Bob" />
...

Where the index of the User array (123 and 456) are ID's associated with the value. I'm trying to update these values in the controller. My thinking is that a Dictionary that maps ID to name would work, but creating the action like:

public void Save(Dictionary<string, string> user) {
    // ...
}

results in the user parameter being null.

So, is passing a Dictionary possible? or, is there another method to achieve this?

Answer 1

It's possible for lists, I'm sure it carries over for dictionaries as well. Read through Model Binding to a List by Phil Haack for some understanding on how list binding works.

You should be able to do this:

<input type="hidden" name="User.Index" value="123" />
<input type="text" name="User[123]" value="Alice" />

<input type="hidden" name="User.Index" value="456" />
<input type="text" name="User[456]" value="Bob" />

Answer 2

See http://www.hanselman.com/blog/ASPNETWireFormatForModelBindingToArraysListsCollectionsDictionaries.aspx for the syntax necessary to bind to a dictionary. Note in particular the example of binding MSFT + AAPL company tickers around halfway down that post.

Answer 3

For ASP.NET MVC 2 use this:

<input type="hidden" name="User[0].Key" value="123" />
<input type="text" name="User[0].Value" value="Alice" />

<input type="hidden" name="User[1].Key" value="456" />
<input type="text" name="User[1].Value" value="Bob" />

You need an extra hidden field User[i].Key. i is zero-based index. It should be uninterrupted.

when you model bind to a dictionary, you're actually binding to an ICollection<KeyValuePair<,>>. So you need User[x].Key and User[x].Value (to reconstitute the KeyValuePair object)

References

• ASP.NET Wire Format for Model Binding to Arrays, Lists, Collections, Dictionaries by Scott Hanselman
• ASP.NET MVC Model Binding Form Inputs To Action Parameters by Marco Magdy