How do we check whether a dynamic clay object has a property?

Question

I have a dynamic object, that I think is implemented with Clay. It has one of two possible property names. I want to use which ever property name is available. The following doesn't work:

dynamic workItemPart = item.WorkItem; // is an Orchard.ContentManagement.ContentPart
var learnMore = workItemPart.LearnMore ?? workItemPart.LearnMoreField;

It throws a Microsoft.CSharp.RuntimeBinder.RuntimeBinderException:

does not contain a definition for 'LearnMore'

How do we check if a dynamic Clay object has a property? In JavaScript, for instance, we can do the following.

var workItemPart = {
    LearnMoreField: "Sure"    
    }
console.log(workItemPart.LearnMore || workItemPart.LearnMoreField);

Is there anything this concise in C# with Clay?

https://twitter.com/bleroy/status/497078654405312512

if workItemPart is dynamic it shouldn't give you a compiler error. I don't really understand what do you mean by dynamic here — Selman Genç, Aug 05 '14 at 22:48
@Selman22 That actually wasn't the answer. Thank you, though, as I had assigned it to a `var` not a `dynamic`. — Shaun Luttin, Aug 05 '14 at 22:49
but be aware that if it hasn't the property `LearnMore` it will throw `RuntimeBinderException` at runtime. if the property does exists but is null then it won't be a problem — Selman Genç, Aug 05 '14 at 22:51
It hasn't the property. That is what I want to determine. That is the whole question. How do we test whether the object has the property? — Shaun Luttin, Aug 05 '14 at 22:52
Can you cast `Clay` to `IDictionary` and use `ContainsKey("LearnMore")`? — Jacob Seleznev, Aug 05 '14 at 23:05

Darek · Answer 1 · 2014-08-05T23:52:59.700

2

You can also use the indexed approach:

var learnMore = workItemPart["LearnMore"] != null ? 
     workItemPart.LearnMore : workItemPart.LearnMoreField;

Hope this helps.

UPDATE

I'm not sure why it doesn't. Both methods should work.

        dynamic New = new ClayFactory();
        var person = New.Person();
        person.skill = "Outstanding";
        var talent = person.talent;
        var talentTwo = person["talent"];
        var skill = person.talent ?? person.skill;
        Console.WriteLine(skill);
        skill = person.skill ?? person.talent;
        Console.WriteLine(skill);

Perhaps it is Orchard throwing you a curveball ...

Interesting enough, the null-coalesce operator does not process the first test case correctly. However, the standard test succeeds:

        skill = person.talent != null ? person.talent : person.skill;
        Console.WriteLine(skill);

Not sure what to advise you at this point.

edited Aug 05 '14 at 23:52

answered Aug 05 '14 at 22:55

Darek

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That works. I wish there were a more concise way. In JavaScript, for instance, we can be incredibly concise and do the same thing. – Shaun Luttin Aug 05 '14 at 22:57
how does this work ? `dynamic obj = new {Name = "Foo"}; var name = obj["Name"];` throws exception for me. Am I missing something ? – Selman Genç Aug 05 '14 at 23:02
This throws an exception too: `Cannot apply indexing with [] to an expression of type 'Orchard.ContentManagement.ContentPart'` – Shaun Luttin Aug 05 '14 at 23:08
Maybe Orchard.ContentManagement.ContentPart isn't implement with Clay after all. – Shaun Luttin Aug 06 '14 at 17:42
Here is the thing ... I hear war drums already, to go after the Clay creator ... :) If you want loosely typed, use agnostic language, by all means, code in JavaScript. Just glancing over `New.Person()` makes me sick that I even wrote this piece of code to test your particular problem. That's not what C# has been created for. Having said that, if you need an approach which will dynamically create new types with all kinds of functions, there is always T4 templates and dynamic runtime compilation. You can perform all kinds of magic tricks using them. – Darek Aug 06 '14 at 17:50
Orchard doesn't use Clay. – Bertrand Le Roy Aug 06 '14 at 17:58

score 1 · Answer 2 · answered Aug 05 '14 at 22:58

1

You can use an extension method to check if property exists:

public static class Extensions
{
    public static bool HasProperty(this object d, string propertyName)
    {
        return d.GetType().GetProperty(propertyName) != null;
    }
}

Usage:

bool hasProperty = Extensions.HasProperty(workItemPart, "LearnMore");

var learnMore =  hasProperty ? workItemPart.LearnMore : workItemPart.LearnMoreField;

It doesn't look like an extension method though.. since the workItemPart is dynamic you need to call it explicitly by specifying the class name.

answered Aug 05 '14 at 22:58

Selman Genç

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This works too, though it is pretty verbose compared to what JavaScript gives us. Its good parts are so good. – Shaun Luttin Aug 05 '14 at 23:02
This doesn't appear to work either. GetProperty is returning null. – Shaun Luttin Aug 06 '14 at 17:32

score 1 · Answer 3 · answered Sep 17 '15 at 04:50

@Shaun Luttin, quite an old issue in the context of the Orchard cms, but recently I've proposed this pull request that has been committed

So, now you can use the following without throwing an exception

    if (contentItem.SomePart != null)
    if (part.SomeField != null)

The ContentItem and ContentPart classes inherit from System.Dynamic.DynamicObject and override the TryGetMember() method. And, before, if no property found the method returned false

    return false;

Now, even if the result object (the out parameter of the method) is set to null, the method return true which prevents from throwing an exception

    result = null;
    return true;

For more details, see the related PR link above

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How do we check whether a dynamic clay object has a property?

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