How do I add object to an array property of an anonymous object in c#

Question

Most of my studying of the c# was with the earlier releases I am not very familiar with this kind of code. I was provided with this snipped bellow but I am having a hard time to add the products dynamically to the items property of the anonymous object.

  var body = new
     {
        items = new[] {
         new {
            name = "Product 1",
            value = 1000,
            amount = 2
             }

           },
        shippings = new[] {
           new {
            name = "Default Shipping Cost",
            value = 100
               }
             }
      };

The idea would be:

 var body = new { items =  new[]{ new { }  } };

        foreach(Modelos.Produto p in carrinho.Items)
        {
            body.items // add elements  { name = p.name }
        }

You can't add elements to an array without recreating it. You should be using a List. — Ron Beyer
– Ron Beyer, Commented Apr 30, 2018 at 16:59
What is new { items = new[]{ new { } } }; supposed to produce? An anonymous object that has an array of anonymous objects? I don't see the point of such illegibility, I'd keep it to using classes for something like this — Camilo Terevinto
– Camilo Terevinto, Commented Apr 30, 2018 at 17:04
@CamiloTerevinto: It can be useful as a simple way of generating one-off JSON in my experience. It's not that the object is anonymous though - it's the type that's anonymous. — Jon Skeet
– Jon Skeet, Commented Apr 30, 2018 at 17:09
@DaisyShipton Not sure what part of my comment makes it look like I said that the object is anonymous — Camilo Terevinto
– Camilo Terevinto, Commented Apr 30, 2018 at 17:10
@CamiloTerevinto: "An anonymous object that has an array of anonymous objects" It's an object of an anonymous type, that has an array with an anonymous type as the element type. — Jon Skeet
– Jon Skeet, Commented Apr 30, 2018 at 17:10

Joel Coehoorn · Accepted Answer · 2018-04-30 19:28:33Z

2

Try it like this:

var body = new { items =  new[]{ new { }  }.ToList() };

foreach(Modelos.Produto p in carrinho.Items)
{
    body.items.Add( /* ... */ );
}

But note this coding is style is intended to solve some very specific problems, namely working with old COM libraries and inside LinQ queries. You'll quickly find it has significant drawbacks if you try to move much beyond that.

One of those drawbacks (I'd call it a feature) is you're still working with fixed types, meaning the new { } inside that collection initializer became the template for the generic list.

edited Apr 30, 2018 at 19:28

answered Apr 30, 2018 at 17:08

Joel Coehoorn

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4 Comments

Camilo Terevinto Over a year ago

What would be the point of this, though? Since items holds empty anonymous types, you cannot add anything useful to that list, or am I missing something?

Jon Skeet Over a year ago

@CamiloTerevinto: You can add another instance of the same anonymous type. So long as you use the same property names and types, in the same order, that would refer to the same type.

Camilo Terevinto Over a year ago

@DaisyShipton Yes, I know that, and that's exactly why I commented. Having a list of empty anonymous type means you can only add more empty anonymous type (VS gives it this special name)

Jon Skeet Over a year ago

@CamiloTerevinto: I was assuming that Joel's answer just omitted the part in the initial body assignment specifying the properties - that it would be the same as in the question, but with the ToList() part. Basically emphasizing just that you're creating a list, because then you can add to it. It would definitely be helpful for Joel to clarify that.

adjan · Accepted Answer · 2018-04-30 17:07:13Z

0

If you really have no other choice, and I strongly advise to use something else instead (List<T> etc.), you could use Array.Resize() to resize the array and add a new item at its end:

var body = new { items =  new[]{ new { }  } };

foreach(Modelos.Produto p in carrinho.Items)
{
     var array = body.items;
     Array.Resize(ref array, array.Length + 1);
     body.items[body.items.Length - 1] = new {}; // or whatever you want to add here
}

answered Apr 30, 2018 at 17:07

adjan

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Comments

Rafael S. Matias · Accepted Answer · 2018-04-30 17:56:21Z

0

var list = new List<Test>();

        for (int i = 1; i < 20; i++)
        {
            list.Add(new Test($"descrition {i}"));
        }

        var listDynamic = new List<object>();

        foreach (var item in list)
        {
            var properties = item.GetType().GetProperties();
            object expando = new ExpandoObject();
            var p = expando as IDictionary<string, object>;

            foreach (var property in properties)
            {
                var value = item.GetType().GetProperty(property.Name).GetValue(item, null);

                p[property.Name] = value;
            }

            listDynamic.Add(p);
        }

I think this solve your problem.

answered Apr 30, 2018 at 17:56

Rafael S. Matias

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