Is it possible to easily create a JsonReader only (not a JsonFormat!) for a case class in Spray easily?
For reading and writing there is:
implicit val xyzFormat = jsonFormatN(Xyz)
But it picks up JsonFormats for nested types, if a nested type uses a custom serialization you have always write a Format with read() and write() then, which is cumbersome, if you only want to support read or write.
Related
I need to implement an abstract class function, which own a an specific data type. But I need inside my logic layer to make the attribute which is going to be passed as a dynamic data type. But when i Pass it to the function, i am sure that its data type will be as needed. So, i type (product.value.pickedImages) as ListOf5) . But it does an Exception.
The Abstract Class Code Is:
Future<Either<FireStoreServerFailures, List<String>>> uploadProductImages(
{required ListOf5<File> images});
The Implementation Code Is:
Future<Option<List<String>>> _uploadImagesToFirestorage() async {
return await productRepo
.uploadProductImages(
images: (product.value.pickedImages) as ListOf5<File>) // Exception
}
The Exception Is:
The argument type 'ListOf5 < dynamic>' can't be assigned to the
parameter type 'ListOf5 < File>'.
You are trying to cast the List from List<dynamic> to List<String>.
Instead, you should cast each item, using something like this:
void main() {
List<dynamic> a = ['qwerty'];
print(List<String>.from(a));
}
Not sure about the implementation of this ListOf5 though...
The cast (product.value.pickedImages) as ListOf5<File> fails.
It fails because product.value.pickedImages is-not-a ListOf5<File>, but instead of ListOf5<dynamic> (which may or may not currently contain only File objects, but that's not what's being checked).
Unlike a language like Java, Dart retains the type arguments at run-time(it doesn't do "erasure"), so a ListOf5<dynamic> which contains only File objects is really different from a ListOf5<File> at run-time.
You need to convert the ListOf5<dynamic> to a ListOf5<File>.
How to do that depends on the type ListOf5, which I don't know.
For a normal List, the two most common options are:
(product.value.pickedImages).cast<File>(). Wraps the existing list and checks on each read that you really do read a File. It throws if you ever read a non-File from the original list. Perfectly fine if you'll only read the list once.
List<File>.of(product.value.pickedImages). Creates a new List<File> containing the values of product.value.pickedImages, and throws if any of the values are not File objects. Requires more memory (because it copies the list), but fails early in case there is a problem, and for small lists, the overhead is unlikely to be significant. If you read the resulting list many times, it'll probably be more efficient overall.
If the ListOf5 class provides similar options, you can use those. If not, you might have to build a new ListOf5 manually, casting each element of the existing ListOf5<dynamic> yourself.
(If the ListOf5 class is your own, you can choose to add such functionality to the class).
I am trying to understand when does Orika use converters to do the mapping versus direct casting.
I have the following mapping:
Class A {
Map<String, Object> props;
}
Class B {
String bStr;
int bInt;
}
My mapping is defined as props['aStr'] => bStr and props['aInt'] => bInt
When I look at the generated code, I see that for the String case, it uses a converter and calls its convert method for the transformation:
destination.setBStr("" + ((ma.glasnost.orika.Converter)usedConverters[0]).convert(
((java.lang.Object) ((java.util.Map) source.getProps().get("aStr"),
(ma.glasnost.orika.metadata.Type) usedTypes[0]))
But, for the integer case it directly casts it like this:
destination.setBInt((java.lang.Integer)(java.lang.Object) ((java.util.Map)
source.getProps().get("aInt")))
The above line of code ends up giving class cast exception.
For fixing this issue, I was thinking along the lines of using a custom converter but if the above line of code doesn't use the converter then that wont work.
Of course, I can always do this is in my custom mapper but just trying to understand how the code is generated for type conversion.
Thanks!!
In Orika there is two stages: config-time and runtime, as optimization Orika resolve all used converter in the config-time and cache them into each generated mapper so it will be accessible directly O(1) but in the config time it will try to find in a list O(n) of registered converters which one "canConvert" between two given types, canConvert is a method in Converter interface .
So this solution offer the best of the two worlds:
A very flexible way to register a converter with arbitrary conditions
An efficient resolution and conversion operation in the runtime.
Orika by default, leverage the existence of .toString in every object to offer implicit coercion to String for every Object. The problem here is that there is no Converter from Object to Integer.
Maybe this can be an issue of error reporting. Ideally Orika should report that an Object have to be converted to Integer and there is no appropriate converter registered.
I've not been able to find a robust, general op_Dynamic implementation: can anyone point me to one? So far searches have only turned up toys or specific purpose implementations, but I'd like to have one on hand which, say, compares in robustness to C#'s default static dynamic implementation (i.e. handle lots / all cases, cache reflection calls) (it's been a while since I've looked at C#'s static dynamic, so forgive me if my assertions about it's abilities are false).
Thanks!
There is a module FSharp.Interop.Dynamic, on nuget that should robustly handle the dynamic operator using the dlr.
It has several advantages over a lot of the snippets out there.
Performance it uses Dynamitey for the dlr call which implements caching and is a .NET Standard Library
Handles methods that return void, you'll get a binding exception if you don't discard results of those.
The dlr handles the case of calling a delegate return by a function automatically, this will also allow you to do the same with an FSharpFunc
Adds an !? prefix operator to handle invoking directly dynamic objects and functions you don't have the type at runtime.
It's open source, Apache license, you can look at the implementation and it includes unit test example cases.
You can never get fully general implementation of the ? operator. The operator can be implemented differently for various types where it may need to do something special depending on the type:
For Dictionary<T, R>, you'd want it to use the lookup function of the dictionary
For the SQL objects in my article you referenced, you want it to use specific SQL API
For unknown .NET objects, you want it to use .NET Reflection
If you're looking for an implementation that uses Reflection, then you can use one I implemented in F# binding for MonoDevelop (available on GitHub). It is reasonably complete and handles property access, method calls as well as static members. (The rest of the linked file uses it heavily to call internal members of F# compiler). It uses Reflection directly, so it is quite slow, but it is quite feature-complete.
Another alternative would be to implement the operator on top of .NET 4.0 Dynamic Language Runtime (so that it would use the same underlying API as dynamic in C# 4). I don't think there is an implementation of this somewhere out there, but here is a simple example how you can get it:
#r "Microsoft.CSharp.dll"
open System
open System.Runtime.CompilerServices
open Microsoft.CSharp.RuntimeBinder
let (?) (inst:obj) name (arg:'T) : 'R =
// Create site (representing dynamic operation for converting result to 'R
let convertSite =
CallSite<Func<CallSite, Object, 'R>>.Create //'
(Binder.Convert(CSharpBinderFlags.None, typeof<'R>, null)) //'
// Create site for the method call with single argument of type 'T
let callSite =
CallSite<Func<CallSite, Object, 'T, Object>>.Create //'
(Binder.InvokeMember
( CSharpBinderFlags.None, name, null, null,
[| CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null);
CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null) |]))
// Run the method and perform conversion
convertSite.Target.Invoke
(convertSite, callSite.Target.Invoke(callSite, inst, arg))
let o = box (new Random())
let a : int = o?Next(10)
This works only for instance method calls with single argument (You can find out how to do this by looking at code generated by C# compiler for dynamic invocations). I guess if you mixed the completeness (from the first one) with the approach to use DLR (in the second one), you'd get the most robust implementation you can get.
EDIT: I also posted the code to F# Snippets. Here is the version using DLR: http://fssnip.net/2U and here is the version from F# plugin (using .NET Reflection): http://fssnip.net/2V
I have a number of interfaces I use to pass business objects around in my application. Using Ninject, I can do whatever I want with them without needing to know the type of the actual object; in this case, most of them are actually various Linq to Sql objects that implement the interface.
For example, I have a Linq to Sql object called Listing that implements IListing.
Where I've run into a problem is with serialization. I've tried using the built in JsonResult and JsonNet. Both of them attempt to serialize the actual Linq to Sql object, not just the properties defined in the interface type. This leads to circular reference issues, but the larger problem is that I only want the properties defined in the interface being serialized and passed around.
So, is there an elegant way to serialize just the properties defined in an instance of an interface that I pass to a serializer?
You could define a new transport type containing only the properties you need and then use AutoMapper to convert between your domain object to this type which will be used for serialization.
Is it possible to serialize a hierarchy of objects in Flex, send the binary data to a URL for storage/retrieval on/from a server, and deserialize the data to restore the objects' original state?
I know it's possible to convert the objects into an XML format (haven't tried it yet), but I'm hoping to avoid parsing XML and rebuilding the objects manually. It would be nice to have functionality which can serialize/deserialize objects to a simple binary format (I did something similar in the past in Java, though not quite as easily as I would have liked). The 'eval' function in Perl is similar to what I'm looking for, sans saving code, of course.
In pseudo-code, here's what I would like to do:
private var contentToSave:HBox = new HBox();
private function saveState(event:Event):void {
var toSave:HBox = this.contentToSave;
var data:? = /* serialize 'toSave' ActionScript classes to binary data*/;
sendDataToServer(data, filename);
}
private function restoreState(filename):void {
var data:? = getDataFromServer(filename);
var savedData:HBox = /* deserialize binary 'data' to ActionScript classes */;
this.contentToSave = savedData;
}
Take a look at ByteArray.writeObject(). which saves the passed object in AMF format into the byte array. I have not used this function too much, I don't exactly know what kind of objects it can serialize, but definitely not all.
Try the JSON based serialization package in ascorelib.
[...]but I'm hoping to avoid parsing XML and rebuilding the objects manually
AS handles XML just like any other native type. Rest assured. XML is the preferred way of dealing with data you will be pulling off and putting back on a server. Of course, the ascorelib gives you a JSON class -- so you may want to look at that as well.
The 'eval' function in Perl is similar to what I'm looking for, sans saving code, of course.
IIRC, eval is part of the ECMAScript specification (and you will find it in Javascript). But not in AS3.0. It was there to a certain extent in some previous version(s?) but is no longer supported.