Using the C# object initializer syntax I can instantiate an anonymous object like this:
object empData = new { name = "bob", age = 30, salary = 100000 };
But what if I have the initializer stored in a string, e.g.:
string init = "{ name = \"bob\", age = 30, salary = 100000 }";
Whats the best way of converting this string into an instance of the object?
Anonymous classes are C# syntactic sugar (see Remarks section here). csc.exe creates a class with private fields and a read/write property with the type inferred from context. All uses of the object are, again, inferred.
What this means is you cannot create an anonymous class at run time because the CLR sees them no differently than any other class (again, because it is C# syntactic sugar).
So instead:
Use a Dictionary<string,object>
Use JSON.NET, XML or something like it that has some already-defined scheme for parsing a string to get an object. This requires the properties be well-defined, however.
Use System.Reflection.Emit to create the type at run-time, but I see no real benefit to this over just a Dictionary<string,object>
I also have concerns of what you're doing because this as a string very likely means to me that you are accepting user input of some kind. Be wary of the security issues in whatever you do.
It's not possible using anonymous types, however you can do it with Reflection Emit using the TypeBuilder class, specifically TypeBuilder.Create(..).
http://msdn.microsoft.com/en-us/library/system.reflection.emit.typebuilder.createtype.aspx
The best way to do it is to use serialization. But of course, that doesn't use the same string format that you described.
Your object initializer does not have to contain constant values.
string myName="bob";
int myAge=30;
double mySalary=100000;
object empData = new { name = myName, age = myAge, salary = mySalary };
So in your scenario you would have to parse out the individual elements from your string, and perform some conversions on them to coerce them into the types you want.
If you are not married to this particular string format, you can serialize and deserialize your objects and accomplish the same thing using XML much more easily.
There's no direct easy way to do so. Basically, you have these options:
Parse the string manually.
Use the C# compiler to compile that object as a part of an assembly and use reflection to figure out the contents.
(not sure if it's possible, C# 4.0 only): Use C# 4.0 managed compiler classes to parse the expression and infer the stuff.
None of which is ideal in my opinion. I'd consider QueryString like pairs, XML or JSON or some other format that has parsers available out there instead if you have the option and consider storing data in a dictionary instance instead of creating an object for every expression.
I don't think this question answers yours per se, but it will tell you why it's not possible to create anonymous instances of objects using strings in a manner such as you suggest:
How do I create and access a new instance of an Anonymous Class passed as a parameter in C#?
Anonymous types don't have any public fields, consequently while you can do this for a named object, it's not so simple to do it for an anonymous type. That said, there's nothing to stop you [as suggested by BFree] using reflection to emit the MSIL for the anonymous type - which isn't exactly straightforward, but isn't impossible either.
Related
Looking at the new C# 7.0 ValueTuples, I am wondering if they will completely replace Anonymous Types. I understand that ValueTuples are structs and therefore behave a bit differently than Anonymous Types which are classes. I don't see a use-case, however, in which I would prefer using an Anonymous Type over a ValueTuple.
Are there any use-cases where using an Anonymous Type would still be beneficial over using ValueTuples in C# 7.0?
Anonymous types are immutable, ValueTuples are not. This is reflected in the fact that anonymous types expose properties, ValueTuples expose fields. Data binding almost always requires properties.
Plenty of existing code only works with reference types, not with value types. What in particular comes to mind are projections in Entity Framework: projections to value types are simply not implemented.
anonymous types can carry name data inwards, but cannot express name data on signatures
value tuples can express name data on signatures, but cannot carry name data inwards
Signature example:
(int Id, string Name) GetFoo(...) // could also use tuples in args, but not very useful
There is no way of doing this with anonymous types, as you cannot express the anonymous type other than as object on a signature.
"Inwards" example:
by this, I mean passing name data into libraries. For example, if we consider JSON:
var json = SomeJsonConvertAPI(new { Id = 42, Name = "abc" });
the library will be able to see the names Id and Name, and work accordingly (coming up with JSON like {"Id":42,"Name":"abc"}); however, this is not possible with value-tuples - any library, whether using <T> or object or something else, will only see the Item1, Item2, etc - with no mechanism to obtain the name data that exists at the originating site.
What would be nice would be something that is similarly terse to value-tuples and anonymous types, but which can be used in signatures and to pass inwards into libraries; and thus C# 9 gives you records:
record Foo(int Id, string Name);
which is short-hand for a class Foo with members int Id {get;} and string Name {get;} with all the constructor and equality bits you would expect.
I'm working on a deserialization class in .NET, I have to develop a method that provides to me with a variable name that is stored in a string.
I have a string such as:
string string_name = "this_is_going_to_be_var_name";
Now what can I do so that my code dynamically declares a variable named this_is_going_to_be_var_name?
So to clear things up: There will be a deserialization class that will declare variables of the same names as strings provided as input with their PARENT TYPES as per wish of the Higher Level Programmer/User.
For Example: In javascript/jQuery, when I fetch JSON by making a request, the interpreter declares variable(s)/array(s) of the same name and assigns values to them. If {"var_name":"var_value"} is a JSON string, the interpreter will create a variable named var_name and will assign "var_value" to it such as json_data_object.var_name.
No you can't. C# variables are all statically declared.
The best thing you can do is create a dictionary and use keys instead of variable names.
// Replace object with your own type
Dictionary<string, object> myDictionary = new Dictionary<string, object>();
myDictionary.Add("this_is_going_to_be_var_name", value_of_the_variable);
// ...
// This is equivalent to foo($this_is_going_to_be_var_name) in PHP
foo(myDictionary["this_is_going_to_be_var_name"]);
This isn't possible, variable names are defined at compile time, not run time.
One approach is to create a dictionary or hash table to map string names to objects to sort of achieve what you want.
Not sure what you meant by
my code dynamically declares a variable named
this_is_going_to_be_var_name?
but the .Net version of what explode does in PHP is Split:
string[] zz = "this_is_going_to_be_var_name".Split('_');
The only thing that I can think on the moment (I haven't tested it so I have no clue if it is possible), is to have a object of type dynamic and then try to set the fields at runtime using reflection and InvokeMember(), which I can give a chance that it will work since the there is no validation on objects of type dynamic.
UPDATE:
I have tested it with ExpendoObject and InvokeMember doesn't appear to work (at least not with the default binder, but I haven't tested it with DynamicObject and allthough I don't give it to much chances to work you might still try it, you can check out http://msdn.microsoft.com/en-us/library/ee461504.aspx on how to use DynamicObject.
Take a look on Dynamically adding properties to an ExpandoObject which essentially describes a method in which the dynamic object is being cast as a IDictionary and then you can add properties to it by using the standard dictionary access, while they are actually getting properties of the object.
I tested it in a sample project by having a dynamic object of type ExpendoObject and then I add another variable that referenced it using type IDictionary, and then I tried to set and get properties on both, as in the following example:
dynamic test = new ExpandoObject();
//reference the object as a dictionary
var asDictinary = test as IDictionary<string, Object>;
//Test by setting it as property and get as a dictionary
test.testObject = 123;
Console.Write("Testing it by getting the value as if it was a dictionary");
Console.WriteLine(asDictinary["testObject"]);
//Test by setting as dictionary and get as a property
//NOTE: the command line input should be "input", or it will fail with an error
Console.Write("Enter the varible name, ");
Console.Write("note that for the example to work it should the word 'input':");
string variableName = Console.ReadLine();
Console.Write("Enter the varible value, it should be an integer: ");
int variableValue = int.Parse(Console.ReadLine());
asDictinary.Add(variableName, variableValue);
Console.WriteLine(test.input);//Provided that the command line input was "input"
(Still however in your case since you will anyway not access the properties directly in code I don't see the need for it and you would probably be able to use a Dictionary directly, and I don't understand why you need them to be properties of the object, which is only needed if you want to reference them at compile time.
But maybe I am misunderstanding you and you are looking for a dynamic variable and not for a dynamic property [something that is available in PHP using the $$ syntax], if this is the case then note that in c# there are no variables at all as everything is encapsulated in a object).
You can also take a look in How can I dynamically add a field to a class in C# for more answers.
This question already has answers here:
Cast an Anonymous Types in Object and retrieve one Field
(4 answers)
Closed 6 years ago.
I want to read some lookup data from the database, using EF, so I do the following:
public object LocationLookUps()
{
var locationTypes = ClientContext.LocationTypes;
var serviceCategories = ClientContext.ServiceCategories;
var serviceTypes = ClientContext.ServiceTypes;
var timeZones = ClientContext.TimeZones;
return new {locationTypes, serviceCategories, serviceTypes, timeZones};
}
Later, within my consuming code, I want to query each of these types to check whether a given locationType, timeZone, etc... are valid values. If I had returned a List<LocationType>, then I can query it as:
var locationType = list.SingleOrDefault(t => t.LocationTypeCode = "B");
Can you do the same with the anonymous type?
There is no way to return an anonymous type from a method, and by returning object, you are discarding design-time knowledge of the type information. There is no way to do what you're asking.
That does not mean that there isn't a way to do what you want, however. Some options:
return each lookup separately, in four separate methods
create an
AllLookups class which includes typed properties for the four lookups
and return it from the method
use the Repository Pattern and expose methods for specific lookup-related queries each from their own methods
No, you can't. C# is strongly typed. Compiler at compilation time finds all anonymous types and converts them to real types. And all work goes with anonymous types converts to work with this generated real types.
In your code you donn't know a future name of real type. So you can only use
var temp = new {something};
and then use temp localy or by reflection (dynamic keyword) in different places
You return Object. So other code will interpret it like Object. And you can not make cast, because you don't know a name. I suppose you have to make a some ViewModel class that will contain four your fields
I have a dynamic type in C# (Content, a type that inherits DynamicObject). It wraps an inner JSON object containing the data. In TryGetMember I return the requested properties from this inner JSON object. This works just fine in case of simple types (e.g. an int or string property), because .Net converts those values correctly.
But I want to use properties with more complex types:
dynamic content = Content.Load(id);
IEnumerable<Book> bookList = content.Books;
The problem is that in TryGetMember of my class I have no way to know the type that I should convert to (in this case the IEnumerable Book), because binder.ReturnType is always Object. According to this article, this is the normal behavior:
Determining the expected type of a DynamicObject member access
But I find this very hard to believe: how is it possible that the API does not let me know the target type? This way I will have to force developers to use the method syntax to specify the type explicitely:
IEnumerable<Books> bookList = content.Books<IEnumerable<Book>>();
...which is ugly and weird.
You could store Type data alongside the JSON serialized data, but that seems like a rather inefficient method of accomplishing what you're trying to do. If your content isn't truely dynamic (e.g., the content changes, but the basic schema of the object is the same), you could just have precompiled classes for each JSON object type, and serialize the JSON into that class once you receive the data. This way, all of the type data would already be recognized by the compiler at runtime.
It turns out that this is not possible indeed. I ended up creating an extension method (defined in two forms: for dynamic collections and JArrays). That way I can at least get a collection of my Content class and all of the following solutions work:
One line, but a bit long
var members = ((IEnumerable<dynamic>)group.Members).ToContentEnumerable();
Separate lines
IEnumerable<dynamic> members = adminGroup.Members;
foreach (dynamic member in members.ToContentEnumerable())
{
//...
}
Using the method call syntax of the extension method (a bit unusual).
var members = ContentExtensions.ToContentEnumerable(group.Members);
Can I dynamically create a property type and property name for an (anonymous) object if the name and type I get from a string variable?
If you're talking about anonymous types (such as var x = new { Property1 = data1, ...}) then I don't think that you can.
What you might be able to do is create another new anonymous type from the one you already have. Where you want to create Y from X, you could create Y by var Y = new { YProp1 = X.Prop1, YProp2 = X.Prop2, etc}
In c# 4.0 onwards you can use dynamic keyword with DynamicObject object based on dictionary to create/extend properties at runtime very much like JavaScript.
For anonymous classes, no. These are defined at compile-time by the compiler.
C# .NET is a statically typed language, meaning that all classes must be defined at compile time. So, the knee-jerk answer to your question is no.
However, like most languages, there are workarounds that you can use. For instance, you can create a class that has a Dictionary<string,object> type property that will take your property names as keys and your property values as values.
Of course, the downside to this is that you will need to write extra code to verify that the data in the dictionary is valid... so it may not be worth it.