How do I check if a property exists on a dynamic anonymous type in c#?

Question

I have an anonymous type object that I receive as a dynamic from a method I would like to check in a property exists on that object.

....
var settings = new {
                   Filename="temp.txt",
                   Size=10
}
...

function void Settings(dynamic settings) {
var exists = IsSettingExist(settings,"Filename")
}

How would I implement IsSettingExist ?

Solution 1

  public static bool DoesPropertyExist(dynamic settings, string name)
  {
    if (settings is ExpandoObject)
      return ((IDictionary<string, object>)settings).ContainsKey(name);

    return settings.GetType().GetProperty(name) != null;
  }

  var settings = new {Filename = @"c:\temp\q.txt"};
  Console.WriteLine(DoesPropertyExist(settings, "Filename"));
  Console.WriteLine(DoesPropertyExist(settings, "Size"));

Output:

 True
 False

Solution 2

public static bool HasProperty(dynamic obj, string name)
{
    Type objType = obj.GetType();

    if (objType == typeof(ExpandoObject))
    {
        return ((IDictionary<string, object>)obj).ContainsKey(name);
    }

    return objType.GetProperty(name) != null;
}

Solution 3

This works for anonymous types, ExpandoObject, Nancy.DynamicDictionary or anything else that can be cast to IDictionary<string, object>.

    public static bool PropertyExists(dynamic obj, string name) {
        if (obj == null) return false;
        if (obj is IDictionary<string, object> dict) {
            return dict.ContainsKey(name);
        }
        return obj.GetType().GetProperty(name) != null;
    }

Solution 4

if you can control creating/passing the settings object, i'd recommend using an ExpandoObject instead.

dynamic settings = new ExpandoObject();
settings.Filename = "asdf.txt";
settings.Size = 10;
...

function void Settings(dynamic settings)
{
    if ( ((IDictionary<string, object>)settings).ContainsKey("Filename") )
        .... do something ....
}

Solution 5

Merging and fixing answers from Serj-TM and user3359453 so that it works with both ExpandoObject and DynamicJsonObject. This works for me.

public static bool HasPropertyExist(dynamic settings, string name)
{
    if (settings is System.Dynamic.ExpandoObject)
        return ((IDictionary<string, object>)settings).ContainsKey(name);

    if (settings is System.Web.Helpers.DynamicJsonObject)
    try
    {
        return settings[name] != null;
    }
    catch (KeyNotFoundException)
    {
        return false;
    }


    return settings.GetType().GetProperty(name) != null;
}

View more solutions

Comments

[Sebastian]

Possible duplicate of How to detect if a property exists on an ExpandoObject?

[Piotr Kula]

If you find your self heavily relying on dynamic objects its probably worth looking at F# - Nice Avatar by the way

[David MZ]

I can't change it, can I cast to ExpendoObject?

[Whatever Man]

Allowing exceptions to occur and then catching them is not a preferred solution because there is a lot of overhead associated with throwing and catching. It's a last resort only. Exceptions are for designed for situations that should not happen in the course of execution like a network being unavailable. There are much better solutions here.

[evilom]

This does not work on dynamic objects. It always returns null.

[Matas Vaitkevicius]

Fails with RuntimeBinderException and dynamicObj[property].Value when value is actually there ... var value = dynamicObj[property] is enough ... and when it does not exist KeyNotFoundException on Dictionary is thrown... see below...

[Matas Vaitkevicius]

objType.GetProperty(name) != null; returns null on properties that do exist

[Alex McMillan]

objType.GetProperty(name) != null will always return a bool, which (by definition) cannot ever be null.

[Ian Kemp]

@AlexMcMillan Not sure what dimension you live in where Type.GetProperty(string) for a nonexistent property returns anything other than null.

[Ian Kemp]

@evilom @Shikasta_Kashti Are you trying to use this method with an MVC ViewBag? If so, see stackoverflow.com/a/24192518/70345

[Serg]

@IanKemp, AlexMcMillan said objType.GetProperty(name) != null in reply to MatasVaitkevicius comment actually.

[Marco Guignard]

GetProperties() doesn't list dynamic Member on a DynamicObject. There is a dedicated function GetDynamicMemberNames() for that.

[Gaspa79]

Using exceptions for things like these is not recommended. Should've gone for something like casting to JObject and using .Property() != null

[rr789]

Great solution. I needed to add one more IF statement when converting JSON string into JObject...."if (obj is Newtonsoft.Json.Linq.JObject) return ((Newtonsoft.Json.Linq.JObject)obj).ContainsKey(name);"

[Brijesh Kumar Tripathi]

Also worked for me. Wonderful answer Seth Reno. I have also added "if (obj is Newtonsoft.Json.Linq.JObject) return ((Newtonsoft.Json.Linq.JObject)obj).ContainsKey(name);" in above function as suggested by rr789. So please also edit your answer to include it.

[pholpar]

Using the lambda expression Where first, and then Any is redundant, as you can formulate your filtering expression in Anyas well.

[Artem A]

It's not acceptable solution to use exceptions in business logic. 1 grade, 2nd term.

[solublefish]

@Gaspa79. It's a not-uncommon coding convention. Some folks like an "Is" prefix on all boolean properties. Consistency like that can prevent you from having to guess the first few characters of an identifier (after which, Intellisense works), but at the expense of making a little awkward English in cases like this.

[Evan Nagle]

I find the invalid verb tense of the Is prefix to be more confusing than it would be otherwise to use HasProperty. I would also say that using a grammatically-incorrect prefix like this is actually non-idiomatic in C♯.

[ryanwebjackson]

ExpandoObject is not the same thing as anonymous type. Am I wrong about that?

[ryanwebjackson]

Thank you @BrijeshKumarTripathi! This was exactly my scenario.

[Norcino]

A bit of description and links could have been helpful