I saw a tutorial where an extra class is created just to be able to serialize a list of objects, instead of a single object:
I'm using json_serializable to generate some serialization code for my class Preference, but now I want to save a list of preferences using shared_preferences and I get an error obviously.
var sSavedPrefs = json.encode(PreferenceRepo.getSavedPrefs());
prefs.setString(saved_prefs_key, sSavedPrefs );
I used
#JsonSerializable()
class Preference{...}
to make it serializable, but I don't want to create an extra class like
#JsonSerializable()
class Preferences{...}
just to make it work - is there a better way?
I found a way:
Using the setStringList method I could create a List where I added each serialized object one by one without needing an extra list class. I also noticed that json.encode might not have been the right method to use, I saw jsonEncode in another tutorial and used it instead:
List<String> savedPrefsJson = [];
for (Preference savedPref in PreferenceRepo.savedPrefs) {
String savedPrefJson = jsonEncode(savedPref);
savedPrefsJson.add(savedPrefJson);
}
prefs.setStringList(saved_prefs_key, savedPrefsJson);
Related
I have a #PlanningSolution class, that has one field with a custom List implementation as type.
When solving I run into the following issue (as described in the optaplanner documentation):
java.lang.IllegalStateException: The cloneCollectionClass (class java.util.ArrayList) created for originalCollectionClass (class Solution$1) is not assignable to the field's type (class CustomListImpl).
Maybe consider replacing the default SolutionCloner.
As this field has no impact on planning, can I prevent FieldAccessingSolutionCloner from trying to clone that particular field e.g. by adding some annotation? I dont want to provide a complete custom SolutionCloner.
When inspecting the sources of FieldAccessingSolutionCloner I found out that I only needed to override the method retrieveCachedFields(...) or constructCloneCollection(...) so I tried to extend FieldAccessingSolutionCloner but then I need a public no-args-constructor. There I dont know how to initialise the field solutionDescriptor in the no-args-constructor to use my ExtendedFieldAccessingSolutionCloner as solution cloner.
If the generic solution cloner decided to clone that List, there is probably a good reason for it do so: one of the the elements in that list probably has a reference to a planning entity or the planning solution - and therefore the entire list needs to be planning cloned.
If that's not the case, this is a bug in OptaPlanner. Please provide the classes source code of the class with that field and the CustomListImpl class too, so we can reproduce and fix it.
To supply a custom SolutionCloner, follow the docs which will show something like this (but this is a simple case without chained variables, so it's easy to get right, but solution cloning is notoriously difficult!).
#PlanningSolution(solutionCloner = VaccinationSolutionCloner.class)
public class VaccinationSolution {...}
public class VaccinationSolutionCloner implements SolutionCloner<VaccinationSolution> {
#Override
public VaccinationSolution cloneSolution(VaccinationSolution solution) {
List<PersonAssignment> personAssignmentList = solution.getPersonAssignmentList();
List<PersonAssignment> clonedPersonAssignmentList = new ArrayList<>(personAssignmentList.size());
for (PersonAssignment personAssignment : personAssignmentList) {
PersonAssignment clonedPersonAssignment = new PersonAssignment(personAssignment);
clonedPersonAssignmentList.add(clonedPersonAssignment);
}
return new VaccinationSolution(solution.getVaccineTypeList(), solution.getVaccinationCenterList(), solution.getAppointmentList(),
solution.getVaccinationSlotList(), clonedPersonAssignmentList, solution.getScore());
}
}
I'm new to Kotlin, so apologies if I'm not articulating concepts correctly. I have an instance of an Entity
[TestEntity(applicationId=1, timestamp=2018-01-24T18:40:30, issueState=MA, product=test, status=sold, paymentMode=VISA, premium=null)]
I am writing a service that is going to take these keys and use them to create the headers of a report. The keys may change depending on the type of report the user is trying to generate, which will have an impact on the Entity that will be instantiated.
I want to be able to iterate over this Entity so that I can create an array to use for the headers. Any thoughts on how I do this?
I think the cleanest solution is storing values in a map and delegating properties to it.
Don't think you can otherwise iterate over class fields without some verbose getter chain or ugly reflection shenanigans.
For example here you can access map fields as if they were class fields, but can also easily iterate over map.
data class TestEntity(val map : Map<String, Any>){
val appId : Int by map
val timeStamp : Long by map
(... more fields)
}
In my Google Web Toolkit project, I got the following error:
com.google.gwt.user.client.rpc.SerializationException: Type ‘your.class.Type’ was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.
What are the possible causes of this error?
GWT keeps track of a set of types which can be serialized and sent to the client. your.class.Type apparently was not on this list. Lists like this are stored in .gwt.rpc files. These lists are generated, so editing these lists is probably useless. How these lists are generated is a bit unclear, but you can try the following things:
Make sure your.class.Type implements java.io.Serializable
Make sure your.class.Type has a public no-args constructor
Make sure the members of your.class.Type do the same
Check if your program does not contain collections of a non-serializable type, e.g. ArrayList<Object>. If such a collection contains your.class.Type and is serialized, this error will occur.
Make your.class.Type implement IsSerializable. This marker interface was specifically meant for classes that should be sent to the client. This didn't work for me, but my class also implemented Serializable, so maybe both interfaces don't work well together.
Another option is to create a dummy class with your.class.Type as a member, and add a method to your RPC interface that gets and returns the dummy. This forces the GWT compiler to add the dummy class and its members to the serialization whitelist.
I'll also add that if you want to use a nested class, use a static member class.
I.e.,
public class Pojo {
public static class Insider {
}
}
Nonstatic member classes get the SerializationException in GWT 2.4
I had the same issue in a RemoteService like this
public List<X> getX(...);
where X is an interface. The only implementation did conform to the rules, i.e. implements Serializable or IsSerializable, has a default constructor, and all its (non-transient and non-final) fields follow those rules as well.
But I kept getting that SerializationException until I changed the result type from List to X[], so
public X[] getX(...);
worked. Interestingly, the only argument being a List, Y being an interface, was no problem at all...
I have run into this problem, and if you per chance are using JPA or Hibernate, this can be a result of trying to return the query object and not creating a new object and copying your relavant fields into that new object. Check the following out, which I saw in a google group.
#SuppressWarnings("unchecked")
public static List<Article> getForUser(User user)
{
List<Article> articles = null;
PersistenceManager pm = PMF.get().getPersistenceManager();
try
{
Query query = pm.newQuery(Article.class);
query.setFilter("email == emailParam");
query.setOrdering("timeStamp desc");
query.declareParameters("String emailParam");
List<Article> results = (List<Article>) query.execute(user.getEmail
());
articles = new ArrayList<Article>();
for (Article a : results)
{
a.getEmail();
articles.add(a);
}
}
finally
{
pm.close();
}
return articles;
}
this helped me out a lot, hopefully it points others in the right direction.
Looks like this question is very similar to what IsSerializable or not in GWT?, see more links to related documentation there.
When your class has JDO annotations, then this fixed it for me (in addition to the points in bspoel's answer) : https://stackoverflow.com/a/4826778/1099376
I'd like to use for table storage an entity like this:
public class MyEntity
{
public String Text { get; private set; }
public Int32 SomeValue { get; private set; }
public MyEntity(String text, Int32 someValue)
{
Text = text;
SomeValue = someValue;
}
}
But it's not possible, because the ATS needs
Parameterless constructor
All properties public and
read/write.
Inherit from TableServiceEntity;
The first two, are two things I don't want to do. Why should I want that anybody could change some data that should be readonly? or create objects of this kind in a inconsistent way (what are .ctor's for then?), or even worst, alter the PartitionKey or the RowKey. Why are we still constrained by these deserialization requirements?
I don't like develop software in that way, how can I use table storage library in a way that I can serialize and deserialize myself the objects? I think that as long the objects inherits from TableServiceEntity it shouldn't be a problem.
So far I got to save an object, but I don't know how retrieve it:
Message m = new Message("message XXXXXXXXXXXXX");
CloudTableClient tableClient = account.CreateCloudTableClient();
tableClient.CreateTableIfNotExist("Messages");
TableServiceContext tcontext = new TableServiceContext(account.TableEndpoint.AbsoluteUri, account.Credentials);
var list = tableClient.ListTables().ToArray();
tcontext.AddObject("Messages", m);
tcontext.SaveChanges();
Is there any way to avoid those deserialization requirements or get the raw object?
Cheers.
If you want to use the Storage Client Library, then yes, there are restrictions on what you can and can't do with your objects that you want to store. Point 1 is correct. I'd expand point 2 to say "All properties that you want to store must be public and read/write" (for integer properties you can get away with having read only properties and it won't try to save them) but you don't actually have to inherit from TableServiceEntity.
TableServiceEntity is just a very light class that has the properties PartitionKey, RowKey, Timestamp and is decorated with the DataServiceKey attribute (take a look with Reflector). All of these things you can do to a class that you create yourself and doesn't inherit from TableServiceEntity (note that the casing of these properties is important).
If this still doesn't give you enough control over how you build your classes, you can always ignore the Storage Client Library and just use the REST API directly. This will give you the ability to searialize and deserialize the XML any which way you like. You will lose the all of the nice things that come with using the library, like ability to create queries in LINQ.
The constraints around that ADO.NET wrapper for the Table Storage are indeed somewhat painful. You can also adopt a Fat Entity approach as implemented in Lokad.Cloud. This will give you much more flexibility concerning the serialization of your entities.
Just don't use inheritance.
If you want to use your own POCO's, create your class as you want it and create a separate tableEntity wrapper/container class that holds the pK and rK and carries your class as a serialized byte array.
You can use composition to achieve what you want.
Create your Table Entities as you need to for storage and create your POCOs as wrappers on those providing the API you want the rest of your application code to see.
You can even mix in some interfaces for better code.
How about generating the POCO wrappers at runtime using System.Reflection.Emit http://blog.kloud.com.au/2012/09/30/a-better-dynamic-tableserviceentity/
It seems that serializing Entity Framework objects into JSON is not possible using either WCF's native DataContractJsonSerializer or ASP.NET's native JavaScript serializer. This is due to the reference counting issues both serializers reject. I have also tried Json.NET, which also fails specifically on a Reference Counting issue.
Edit: Json.NET can now serialize and deserialize Entity Framework entities.
My objects are Entity Framework objects, which are overloaded to perform additional business functionality (eg. authentication, etc.) and I do not want to decorate these classes with platform-specific attributes, etc. as I want to present a platform-agnostic API.
I've actually blogged about the individual steps I went though at https://blog.programx.co.uk/2009/03/18/wcf-json-serialization-woes-and-a-solution/
Have I missed something obvious?
The way I do this is by projecting the data I want to serialize into an anonymous type and serializing that. This ensures that only the information I actually want in the JSON is serialized, and I don't inadvertently serialize something further down the object graph. It looks like this:
var records = from entity in context.Entities
select new
{
Prop1 = entity.Prop1,
Prop2 = entity.Prop2,
ChildProp = entity.Child.Prop
}
return Json(records);
I find anonymous types just about ideal for this. The JSON, obviously, doesn't care what type was used to produce it. And anonymous types give you complete flexibility as to what properties and structure you put into the JSON.
Microsoft made an error in the way they made EF objects into data contracts. They included the base classes, and the back links.
Your best bet will be to create equivalent Data Transfer Object classes for each of the entities you want to return. These would include only the data, not the behavior, and not the EF-specific parts of an entity. You would also create methods to translate to and from your DTO classes.
Your services would then return the Data Transfer Objects.
Based off of #Craig Stuntz answer and similar to a DTO, for my solution I have created a partial class of the model (in a separate file) and a return object method with how I want it using only the properties that will be needed.
namespace TestApplication.Models
{
public partial class Employee
{
public object ToObject()
{
return new
{
EmployeeID = EmployeeID,
Name = Name,
Username = Username,
Office = Office,
PhoneNumber = PhoneNumber,
EmailAddress = EmailAddress,
Title = Title,
Department = Department,
Manager = Manager
};
}
}
}
And then I call it simply in my return:
var employee = dbCtx.Employees.Where(x => x.Name == usersName).Single();
return employee.ToObject();
I think the accepted answer is more quick and easy, I just use my method to keep all of my returns consistent and DRY.
My solution was to simply remove the parent reference on my child entities.
So in my model, I selected the relationship and changed the Parent reference to be Internal rather than Public.
May not be an ideal solution for all, but worked for me.
One more solution if you want to have better code consistency is to use JavaScriptConverter which will handle circular reference dependencies and will not serialize such references.
I've blogged about here:
http://hellowebapps.com/2010-09-26/producing-json-from-entity-framework-4-0-generated-classes/
FYI I found an alternative solution
You can set the parent relationship as private so then the properties are not exposed during the translation removing the infinite property loop
I battled with this problem for days,
Solution. Inside your edmx window.
- right click and add code generation item
- Select Code tab
- select EF 4x.POCOC Entity Generator
If you don't see it, then you will have to install it with nuget, search EF.
The Entity generator will generate all you complex type and entity object into simple classes to serialize into json.
I solved it by getting only object types from System namespace, and then convert them to Dictionary and then add them to list. Works good for me :)
It looks complicated, but this was the only generic solution that worked for me...
I'm using this logic for a helper I'm making, so it's for a special use where I need to be able to intercept every object type in entity object, maybe someone could adapt it to his use.
List<Dictionary<string, string>> outputData = new List<Dictionary<string, string>>();
// convert all items to objects
var data = Data.ToArray().Cast<object>().ToArray();
// get info about objects; and get only those we need
// this will remove circular references and other stuff we don't need
PropertyInfo[] objInfos = data[0].GetType().GetProperties();
foreach (PropertyInfo info in objInfos) {
switch (info.PropertyType.Namespace)
{
// all types that are in "System" namespace should be OK
case "System":
propeties.Add(info.Name);
break;
}
}
Dictionary<string, string> rowsData = null;
foreach (object obj in data) {
rowsData = new Dictionary<string, string>();
Type objType = obj.GetType();
foreach (string propertyName in propeties)
{
//if You don't need to intercept every object type You could just call .ToString(), and remove other code
PropertyInfo info = objType.GetProperty(propertyName);
switch(info.PropertyType.FullName)
{
case "System.String":
var colData = info.GetValue(obj, null);
rowsData.Add(propertyName, colData != null ? colData.ToString() : String.Empty);
break;
//here You can add more variable types if you need so (like int and so on...)
}
}
outputData .Add(rowsData); // add a new row
}
"outputData " is safe for JSON encode...
Hope someone will find this solution helpful. It was fun writing it :)