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Dynamic Object Intellisense
(3 answers)
Closed 8 years ago.
My code is like this
var eventDocs = new List<dynamic>();
foreach (var node in eventtypeNode.GetDescendantNodes())
{
string files = node.GetProperty("document").Value;
eventDocs.Add(new { Id = node.Id, Name = node.Name, CreatedOn = node.CreateDate, Path = files });
}
This works good. Now I am trying to fetch the data out of this dynamic list
foreach (var eventDoc in eventDocs)
{
eventDoc.---- //nothing comes on intellisence
}
Nothing comes on IntelliSense? Am I doing anything wrong?
You won't get anything from Intellisense precisely because you've got a List<dynamic>. You're saying, "I don't know at compile-time what this list will contain. When I access members of the elements, just bind that dynamically at execution-time."
Given that you're deferring binding to execution time, why would you be surprised that Intellisense can't tell what will be in the list?
It looks to me like you should change your code to use a LINQ query to start with - then you can have a list with a known element type, which will be an anonymous type.
var eventDocs = eventtypeNode.GetDescendantsNodes()
.Select(node => new { Id = node.Id,
Name = node.Name,
CreatedOn = node.CreateDate,
Path = node.GetProperty("document").Value })
.ToList();
You cannot access dynamic members like this, try GetDynamicMemberNames() and GetMetaObject method
Intellisense will not show suggestions, since the data is dynamic, and it doesn't know what to show.
But you know what it contains. So just code and you'll be fine.
Also, you don't need dynamic objects here. Since what you want is well-defined just define your class with necessary properties and methods and then create the list:
List<YourClass> list = new List<YourClass>();
And then Intellisense will become intelligent enough to show the suggestions ;)
Related
Consider the following code:
foreach (Type formType in allFormsToLoopThrough)
{
var nonPriorityForm = _context.Query(formType);
foreach (var nonpriority in nonPriorityForm)
{
var name = nonpriority.GetType().Name;
MyWorkAssignmentDTO form = new MyWorkAssignmentDTO
{
FormName = formType.Name
Id = nonpriority.Id
};
}
}
This snippet is looping thought a list of types.
Each type is taken from the list and passed to a Query function that returns an IQueryable - basically a list of records in a given table in a database that matches the type.
Then for each of the record sets that come back, I want to loop through those and from each create a new instance of MyWorkAssignmentDTO. I am only interested in a form name (which I can get from formType) but I cannot get nonpriority.Id
I know for sure that every nonpriority will have an Id once it is resolved in the loop.
What I can't do is implement this to work at run time.
Can anyone help?
I was able to use the dynamic keyword instead of var. While I lose compile time validation, this gets me over the line when I know for sure there will be an Id.
dynamic nonPriorityForm = _context.Query(formType);
I'm using TweetInvi to grab a bunch of tweets that match a specified hashtag. I do this with the following:
var matchingTweets = Search.SearchTweets(hashtag);
This returns an IEnumerable (named ITweet, interface of Tweet), however I cannot create a List<> of Tweets, because Tweet is a static type.
I made, instead, a list of objects, using:
List<object> matches = matchingTweets.Cast<object>().ToList();
However, although each member of the matchingTweets IEnumerable has a number of properties, I cannot access them using:
long tweetID = matches[i].<property>;
Using matches[i].ToString() returns the tweet content, so how can I effectively cast the results in matchingTweets to a list, and subsequently access the properties of those list members? I would ideally like to avoid using dynamic.
In your example above you were trying to grab the ID from the tweet. ITweet implements ITweetIdentifier which contains the Id property. You can literally just access it by:
var matchingTweets = Search.SearchTweets(hashtag);
//Grab the first 5 tweets from the results.
var firstFiveTweets = matchingTweets.Take(5).ToList();
//if you only want the ids and not the entire object
var firstFiveTweetIds = matchingTweets.Take(5).Select(t => t.Id).ToList();
//Iterate through and do stuff
foreach (var tweet in matchingTweets)
{
//These are just examples of the properties accessible to you...
if(tweet.Favorited)
{
var text = tweet.FullText;
}
if(tweet.RetweetCount > 100)
{
//TODO: Handle popular tweets...
}
}
//Get item at specific index
matchingTweets.ElementAt(index);
I don't know exactly what you want to do with all the info, but since the SearchTweets returns a IEnumerable of ITweets you have access to anything an ITweet has defined.
I highly recommend looking through their wiki. It's pretty well organized and gives you clear examples of some basic tasks.
It makes sense you cannot access the properties. You cast it into object so you can only access the objects properties and methods (that like you said might have been overridden).
It should be fine to just access it like this:
List<ITweet> tweets = matchingTweets.Take(5).ToList();
What you can do is project it to a new object of yours:
var tweets = matchingTweets.Select(item => new {
property1 = item.property1,
property2 = item.property2
})
.Take(5).ToList();
Then you will be able to access what you need. Now, if you need to share this data outside the scope of that function create a DTO object and initialize it instead of the anonymous type.
Depending on the size of the project and amount of effort usually it is in any case a good practice to create a layer of DTO objects when you interact with an external service like this. Then if their models changed you can contain your changes only to the DTOs.
If all you want are the ids of the first 5 then:
var ids = matchingTweets.Take(5).Select(item => item.id).ToList();
Recently I asked a more general question about getting properties of model through foreign key.
Now I moved a bit further but still have no idea how transform objects on the fly.
What I've got is an IEnumerable collection which I get through repository
regionRaw = unitOfWork.RegionRepository.Get(
keyOrder: q => q.OrderBy(d => d.RegionID),
filter: p => p.FullName.Contains(lastname) || p.ShortName.Contains(lastname),
orderBy: jtSorting,
includeProperties: "District, ISO31662, GOST767Region");
Further I am going to export data from this collection to Excel. So I need a select statement that gets all the fields I need.
dt = regionRaw
.Select(x => new
{
ISO = x.ISO31662.GOSTName,
DistrictName = x.District.ShortName
})
I do not want to enumerate all the fields I need like on the top.
I am able to make a method that recognizes which of the fields have simple values and which have objects referenced through foreign key. And then that method will return a list of properties.
Now I need some way to write something like a foreach inside select. I see something like this:
dt = regionRaw
.Select(x => new
{
foreach (prop in propList)
{
prop.PropertyName = x.GetType()
.GetProperty(prop.TableName)
.GetValue(x, null).GetType()
.GetProperty(prop.PropertyName)
.GetValue(
x.GetType().GetProperty(prop.TableName).GetValue(x, null),
null);
}
}
Where propList is a collection of properties that I get before.
I do totally realize that upper code is more a pseudo-code but I have no idea how to realize this in .NET.
So if you can suggest some solution for this task I will be very grateful. Or maybe you could explain that all this is a bad idea and shouldn't be realized.
You wont be able to create an anonymous type with dynamic properties as anon types are created during compile and your properties are created during execution.
But why do you need strongly typed properties if you're not going to code against them, as you wont know them until someone executes the query?
Expando object may be of use to you?http://msdn.microsoft.com/en-us/library/system.dynamic.expandoobject.aspx
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Use of var keyword in C#
After discussion with colleagues regarding the use of the 'var' keyword in C# 3 I wondered what people's opinions were on the appropriate uses of type inference via var?
For example I rather lazily used var in questionable circumstances, e.g.:-
foreach(var item in someList) { // ... } // Type of 'item' not clear.
var something = someObject.SomeProperty; // Type of 'something' not clear.
var something = someMethod(); // Type of 'something' not clear.
More legitimate uses of var are as follows:-
var l = new List<string>(); // Obvious what l will be.
var s = new SomeClass(); // Obvious what s will be.
Interestingly LINQ seems to be a bit of a grey area, e.g.:-
var results = from r in dataContext.SomeTable
select r; // Not *entirely clear* what results will be here.
It's clear what results will be in that it will be a type which implements IEnumerable, however it isn't entirely obvious in the same way a var declaring a new object is.
It's even worse when it comes to LINQ to objects, e.g.:-
var results = from item in someList
where item != 3
select item;
This is no better than the equivilent foreach(var item in someList) { // ... } equivilent.
There is a real concern about type safety here - for example if we were to place the results of that query into an overloaded method that accepted IEnumerable<int> and IEnumerable<double> the caller might inadvertently pass in the wrong type.
Personally I find the circumstances you describe far from questionable, since there is no point in repeating yourself unless you specifically want the static type of a variable to be different than the static type of the expression used to initialize the variable. For example:
IEnumerable<int> foo = new List<int>(); // It's IEnumerable on purpose
Furthermore, there are absolutely no type safety concerns with var. The point is not that the variable can be of "any" type. It is of a very specific type, but you simply do not care to spell that type out.
I'm only using it as a place holder until I'm sure which datatypes I'm using.
Sure this is a short answer but I think it's pretty close that when you should use the var keyword.
the var keyword is used as shorthand in the language, but isn't a .NET type. The compiler must know the type of the variable to use the var keyword - so it is type-safe.
I personally only use it if the type name is also used in the assignment and the name is possible too long to duplicate in the code.
var dictionary = new Dictionary<string, string>();
It is also used for anonymous types (but still, the compiler must know the signature of the anonymous type).
var fred = new { Age = 23, Name = "Fred" };
This method is used commonly in the select clause of LINQ queries.
Just an "abstraction" or "syntax sugar" to be able to write a code without specifying first the type (this is no your first cases)
In second case: LINQ queries, instead, to rapresent some unknown, dynamic, not concrete, if you wish, type.
could be:
var results = from item in someList
where item != 3
select item; //item a class instance
could be
var results = from item in someList
where item != 3
select item.ItemName; //string property of that class
could be
var results = from item in someList
where item != 3
select new {item.ItemName, item.ID}; //unknown type dynamically generated, that conains the string and integer, like result
As far as I know var remains strong typed. The compiler calculated what the proper type should be. In fact it has no real meaning.
It is only a trick to reduce the number of manipulations. For instance when you change a type in one class, this can result in a cascade of modification. But its only a way to migrate work from the programmer to the compiler.
For instance your Linq query will result in a type IEnumerable<TA>. When you change some class so the result will be IEnumerable<TB> there is no need to change this part of the code.
I want the ability to grab an anonymous type from my view, that was established by the corresponding controller. According to this article, such an ability becomes possible in C# 4.0 with the 'dynamic' keyword. However, when I try to find an actual example I find answers ranging from it kinda 'is possible' to it kinda 'is not possible.'
In my case, I have a controller creating this:
XElement headings = XElement.Parse(part.TagList);
var items = from heading in headings.Descendants("heading")
select new {
name = heading.Attribute("name").Value,
tags = heading.Attribute("tags").Value,
content = shapeHelper.List() //This is a dynamic object!!!
}; //can I add 'as dynamic;' here????
In short it would be nice if, without a static type, my view could simply reach into the model like this:
#{
//Currently this next line returns an error saying that
//'object' contains no method 'Count'
int foo = Model.items.Count();
//This 'foreach' works.
foreach(dynamic lineItem in Model.items){
//But this does not work. Gives another "'object' has no definition for 'name'"
<p>#lineItem.name</p> }
}
Possible?
Not sure it's exactly what you're looking for, but you could always use the ViewBag:
Controller
ViewBag.Items = from heading in headings.Descendants("heading")
select new {
name = heading.Attribute("name").Value,
tags = heading.Attribute("tags").Value,
content = shapeHelper.List()
};
View
ViewBag.Items.First().content;