Expressions on dynamic objects

[NickDarvey]

Hi,

I'm wondering what the story is for System.Linq.Dynamic.Core and types that aren't known till runtime. Is this supported right now, and if it's not, will it be one day?

Right now, I have an IEnumerable<dynamic> I can that I'd like to query. Is there any way I can compose a query on top of that? Is there any other way you know of for handling this case?
(The collection contains ExpandoObjects from a JSON payload deserialized by Json.NET. I see you have a test for JObjects but we don't want to be bound to that type as we may have multiple serializers.)

There is a test in there for verifying a Select on a collection of dynamic objects, but it's disabled right now.

Repro

Run this test.

//[Fact]
public void ExpressionTests_Select_ExpandoObjects()
{
    //Arrange
    dynamic a = new ExpandoObject();
    a.Name = "a";
    a.BlogId = 100;
    dynamic b = new ExpandoObject();
    b.Name = "b";
    b.BlogId = 100;
    var list = new List<dynamic> { a, b };
    IQueryable qry = list.AsQueryable();

    var result = qry.Select("it").Select("BlogId");

    //Assert
    Assert.Equal(new[] { 100, 200 }, result.ToDynamicArray<int>());
}

Expected

Passes.

Actual

It's commented out. It fails when running it:

Message: System.Linq.Dynamic.Core.Exceptions.ParseException : No property or field 'BlogId' exists in type 'Object'

[StefH]

Also related to #132

[StefH]

A possible solution could be that a new class is defined in this library which keeps the information about the properties.
And the properties can be defined with the help from https://github.com/StefH/System.Linq.Dynamic.Core/blob/10fc9a2ec8677f638210804c0ca636de021e6c9a/src/System.Linq.Dynamic.Core/DynamicProperty.cs

So prototype code would be:

var property1 = new DynamicProperty("BlogId", typeof(int));
var property2 = new DynamicProperty("Name", typeof(string));
var a = new DynamicObject(property1, property2);
a.Name = "a";
a.BlogId = 100;

var list = new List<dynamic> { a, a };
IQueryable qry = list.AsQueryable();

var result = qry.Select("it").Select("BlogId"); // At this point the library should understand that the objects special.

// Maybe update the interface so that the type-information is also added?
// like:
var result = qry.Select(new [ property1, property2 ], "it").Select("BlogId");

[jogibear9988]

Or we use: https://msdn.microsoft.com/en-us/library/system.dynamic.dynamicobject.getdynamicmembernames.aspx

[StefH]

Hello @NickDarvey and @jogibear9988,

I've written some code which I use in WireMock.net which generated a select string based on a JObject. Code is here https://gist.github.com/StefH/27058744b2268fe8069c2b9641804214

And works like:

// Assign
var j = new JObject
{
    {"U", new JValue(new Uri("http://localhost:80/abc?a=5"))},
    {"N", new JValue((object) null)},
    {"G", new JValue(Guid.NewGuid())},
    {"Flt", new JValue(10.0f)},
    {"Dbl", new JValue(Math.PI)},
    {"Check", new JValue(true)},
    {"Items", new JArray(new[] {new JValue(4), new JValue(8)})},
    {
        "Child", new JObject
        {
            {"ChildId", new JValue(4)},
            {"ChildDateTime", new JValue(new DateTime(2018, 2, 17))},
            {"TS", new JValue(TimeSpan.FromMilliseconds(999))}
        }
    },
    {"Id", new JValue(9)},
    {"Name", new JValue("Test")}
};

// Act
string line = JsonUtils.GenerateDynamicLinqStatement(j);

// Assert
var queryable = new[] {j}.AsQueryable().Select(line);
bool result = queryable.Any("Id > 4");
Check.That(result).IsTrue();

Check.That(line).IsEqualTo("new (Uri(U) as U, null as N, Guid(G) as G, double(Flt) as Flt, double(Dbl) as Dbl, bool(Check) as Check, (new [] { int(Items[0]), int(Items[1])}) as Items, new (int(Child.ChildId) as ChildId, DateTime(Child.ChildDateTime) as ChildDateTime, TimeSpan(Child.TS) as TS) as Child, int(Id) as Id, string(Name) as Name)");

This could be a solution for your problem?
Closing this issue for now.