At any point of time i will be setting only one setter method but the JsonProperty name should be same for both . when i am compiling this i am getting an exception. How to set the same name for both .?
public String getType() {
return type;
}
#JsonProperty("Json")
public void setType(String type) {
this.type = type;
}
public List<TwoDArrayItem> getItems() {
return items;
}
#JsonProperty("Json")
public void setItems(List<TwoDArrayItem> items) {
this.items = items;
}
Jackson tends to favor common scenarios and good design choices for annotation support.
Your case represents a very uncommon scenario. You have one field having two different meanings in different contexts. Typically this would not be a favourable data format since it adds messy logic to the consumer on the other end...they need to divine what the "Json" property should mean in each case. It would be cleaner for the consumer if you just used two different property names. Then it would be sufficient to simply check for the presence of each property to know which alternative it's getting.
Your Java class also seems poorly designed. Classes should not have this type of context or modes, where in one context a field is allowed, but in another context it's not.
Since this is primarily a smell with your design, and not serialization logic, the best approach would probably be to correct your Java class hierarchy:
class BaseClass {
}
class SubClassWithItems {
public List<TwoDArrayItem> getItems() {
return items;
}
#JsonProperty("Json")
public void setItems(List<TwoDArrayItem> items) {
this.items = items;
}
}
class SubClassWithType {
public String getType() {
return type;
}
#JsonProperty("Json")
public void setType(String type) {
this.type = type;
}
}
That way your class does not have a different set of fields based on some runtime state. If runtime state is driving what fields your class contains, you're not much better off than with just a Map.
If you can't change that, you're left with custom serialization.
Related
I want to support partial updates with JSON Merge Patch. The domain model is based on the always valid concept and has no public setters. Therefore I can't just apply the changes to the class types. I need to translate the changes to the specific commands.
Since classes have nullable properties I need to be able to distinguish between properties set to null and not provided.
I'm aware of JSON Patch. I could use patch.JsonPatchDocument.Operations to go through the list of changes. JSON Patch is just verbose and more difficult for the client. JSON Patch requires to use Newtonsoft.Json (Microsoft states an option to change Startup.ConfigureServices to only use Newtonsoft.Json for JSON Patch (https://learn.microsoft.com/en-us/aspnet/core/web-api/jsonpatch?view=aspnetcore-6.0).
Newtonsoft supports IsSpecified-Properties that can be used as a solution for JSON Merge Patch in the DTO classes (How to make Json.NET set IsSpecified properties for properties with complex values?). This would solve the problem, but again requires Newtonsoft. System.Text.Json does not support this feature. There is an open issue for 2 years (https://github.com/dotnet/runtime/issues/40395), but nothing to expect.
There is a post that describes a solution with a custom JsonConverter for Web API (https://github.com/dotnet/runtime/issues/40395). Would this solution still be usable for NetCore?
I was wondering if there is an option to access the raw json or a json object inside the controller method after the DTO object was filled. Then I could manually check if a property was set. Web Api closes the stream, so I can't access the body anymore. It seems there are ways to change that behavior (https://gunnarpeipman.com/aspnet-core-request-body/#comments). It seems quite complicated and feels like a gun that is too big. I also don't understand what changes were made for NetCore 6.
I'm surpised that such a basic problem needs one to jump through so many loops. Is there an easy way to accomplish my goal with System.Text.Json and NetCore 6? Are there other options? Would using Newtonsoft have any other bad side effects?
With the helpful comments of jhmckimm I found
Custom JSON serializer for optional property with System.Text.Json. DBC shows a fantastic solution using Text.Json and Optional<T>. This should be in the Microsoft docs!
In Startup I added:
services.AddControllers()
.AddJsonOptions(o => o.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault)
.AddJsonOptions(o => o.JsonSerializerOptions.Converters.Add(new OptionalConverter()));
Since we use <Nullable>enable</Nullable> and <WarningsAsErrors>nullable</WarningsAsErrors> I adapted the code for nullables.
public readonly struct Optional<T>
{
public Optional(T? value)
{
this.HasValue = true;
this.Value = value;
}
public bool HasValue { get; }
public T? Value { get; }
public static implicit operator Optional<T>(T value) => new Optional<T>(value);
public override string ToString() => this.HasValue ? (this.Value?.ToString() ?? "null") : "unspecified";
}
public class OptionalConverter : JsonConverterFactory
{
public override bool CanConvert(Type typeToConvert)
{
if (!typeToConvert.IsGenericType) { return false; }
if (typeToConvert.GetGenericTypeDefinition() != typeof(Optional<>)) { return false; }
return true;
}
public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options)
{
Type valueType = typeToConvert.GetGenericArguments()[0];
return (JsonConverter)Activator.CreateInstance(
type: typeof(OptionalConverterInner<>).MakeGenericType(new Type[] { valueType }),
bindingAttr: BindingFlags.Instance | BindingFlags.Public,
binder: null,
args: null,
culture: null
)!;
}
private class OptionalConverterInner<T> : JsonConverter<Optional<T>>
{
public override Optional<T> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
T? value = JsonSerializer.Deserialize<T>(ref reader, options);
return new Optional<T>(value);
}
public override void Write(Utf8JsonWriter writer, Optional<T> value, JsonSerializerOptions options) =>
JsonSerializer.Serialize(writer, value.Value, options);
}
}
My test DTO looks like this:
public class PatchGroupDTO
{
public Optional<Guid?> SalesGroupId { get; init; }
public Optional<Guid?> AccountId { get; init; }
public Optional<string?> Name { get; init; }
public Optional<DateTime?> Start { get; init; }
public Optional<DateTime?> End { get; init; }
}
I can now access the fields and check with .HasValue if the value was set. It also works for writing and allows us to stripe fields based on permission.
Class that i want to mock:
TestClass.java
public class testClass(){
public String getDescription(String input){
String value = this.getDetails(input); // i am not going to change this line, hence want to mock this.
//below this i have some complexity logic, which i would like to fix cyclomatic complexity issue
}
private String getDetails(String input){
return "More details for the "+input;
}
}
My questions is how do i mock "this.getDetails(input)" to return some string for testing purpose?
If you've got a class that is big and complex enough that you need to mock a small piece of it, take that as a hint that you're violating the Single Responsibility Principle and properly split up the classes. If you use dependency injection, you can then supply whatever implementation you'd like.
public class TestClass {
/**
* Computes a detail string based on an input. Supply this in the constructor
* for full DI, relax visibility, or add a setter.
*/
private final Function<String, String> detailFunction;
public String getDescription(String input){
String value = detailFunction.apply(input);
// ...
}
}
As a lightweight alternative, you can test an override or spy of your actual class.
#Test public void testTestClassWithOverride() {
TestClass instanceUnderTest = new TestClass() {
#Override public String getDescription(String input) {
return "Predictable value";
}
};
// test your instanceUnderTest here
}
#Test public void testTestClassWithSpy() {
TestClass spyUnderTest = Mockito.spy(new TestClass());
doReturn("Predictable value").when(spyUnderTest).getDescription(anyString());
// test your spyUnderTest here
}
Bear in mind that, though this is an option for you, it shouldn't be your first option: Rather than testing your actual class, you're testing a one-off variant of it, and you've made it so other consumers can subclass your TestClass as well. If possible, write the flexibility you need into the class itself and treat your test as a consumer that plays by the same rules.
First of all, it is a bad practice to make a so-called "partials mocks". This illustrates that your code doesn't follow single responsibility principle that leads to your code being not (or hardly) testable.
I would suggest you to extract getDescription method from your class and use it indirectly via dependency inversion or more concrete - dependency injection (for instance by employing Spring Framework):
public class TestClass() {
private DetailsServiceProvider detailsServiceProvider;
public TestClass(DetailsServiceProvider detailsServiceProvider) {
this.detailsServiceProvider = detailsServiceProvider;
}
public String getDescription(String input) {
String value = detailsServiceProvider.getDetails(input); // i am not going to change this line, hence want to mock this.
//below this i have some complexity logic, which i would like to fix cyclomatic complexity issue
}
}
public interface DetailsServiceProvider {
String getDetails(String input);
}
public class DetailsServiceProviderImpl implements DetailsServiceProvider{
#Override
public String getDetails(String input) {
return "More details for the "+input;
}
}
Then in your test, you could simply:
#Test
public void test() {
DetailsServiceProvider mockedProvider = Mockito.mock(DetailsServiceProvider.class);
//TODO: add scenarios for the mocked object
TestClass target = new TestClass(mockedProvider);
String description = target.getDescription();
//TODO: add assertions
}
If you do not want to struggle with the preferred approach you could use #Spy in Mockito. This will create exactly what you want - a partial mock for your object where part of the methods will be real and another part - mocks:
#Test
public void test() {
TestClass partialMockedObject = Mockito.spy(new TestClass());
Mockito.doReturn("test details").when(partialMockedObject).getDetails();
String description = partialMockedObject.getDescription();
//TODO: add assertions
}
Again, this method is not desired but can be used if no other options are given. Note that this requires getDetails() to be visible in tests, meaning that the private modifier won't work here.
To share data (complexe data ) between pages in my windows phone 8 application I want to implement a singleton, but I want it to be generic, is it possible? I suppose that it creates a new instance for each type isn't it?
public sealed class NavigationContextService<T>
{
private static readonly NavigationContextService<T> instance = new NavigationContextService<T>();
private NavigationContextService()
{
}
public static NavigationContextService<T> Instance
{
get
{
return instance;
}
}
public List<T> ShareList { get; set; }
public T ShareData { get; set; }
}
It is creating a new instance for every type, because it is generic - you want it to be like this (if you start with generics, take a look at some tutorials, blogs or MSDN - you will easily find many in the internet).
It is still a singleton. When you use
NavigationContextService<string>.Instance.ShareList.Add("Text");
then you have one Instance for type string. Generics helps a lot when you want to create same methods/classes that differ in type.
On the other hand if you want to create Singleton that will hold different types then you can for example modify your class to be non Generic like this:
public sealed class NavigationContextServiceNonGeneric
{
private static readonly NavigationContextServiceNonGeneric instance = new NavigationContextServiceNonGeneric();
private NavigationContextServiceNonGeneric() { ShareList = new List<object>(); }
public static NavigationContextServiceNonGeneric Instance
{ get { return instance; } }
public List<object> ShareList { get; set; }
public object ShareData { get; set; }
}
As you can see in the code above I haven't defined the 'exact' type of shared data - it is object type. Then you can easily hold most of data with it:
NavigationContextServiceNonGeneric.Instance.ShareList.Add("Text");
NavigationContextServiceNonGeneric.Instance.ShareList.Add(3);
NavigationContextServiceNonGeneric.Instance.ShareList.Add(3.0f);
It is singleton, which can hold different types of shared data. BUT it has also disavantages - the main is that you have to remember what type of data you hold and in what order. In my opinion Generic version is better because of that fact.
Everything depends on the purpose of your code. There may be easier and better ways that those two approaches.
As for the Page Navigation, you can for example try to use a method from this article - you extend Navigation service to pass the object:
public static class Extensions
{
private static object Data;
public static void Navigate(this NavigationService navigationService, Uri source, object data)
{
Data = data;
navigationService.Navigate(source);
}
public static object GetNavigationData(this NavigationService service) { return Data; }
}
Then you use it:
NavigationService.Navigate(yourUri, DataToPass);
After Navigation you can get your data:
string myTextData = NavigationService.GetNavigationData() as string;
This method has to disadvantages: it is not type-safe and your data won't be preserved in Tombstone mode.
As for the second disadvantage you can easily use PhoneApplicationService.State Property for the purpose of Page Navigation - it is a dictionary (which is preserved while tombstoning):
PhoneApplicationService.Current.State.Add("data", yourData);
Then when you want to get your data:
yourDataType yourData = PhoneApplicationService.Current.State["data"] as yourDataType;
There are also more ways in which you can pass the data.
I've inherited a system that uses the Castle Windsor IRepository pattern to abstract away from the DAL which is LinqToSQL.
The main problem that I can see, is that IRepository only implements IEnumerable. So even the simplest of queries have to load ALL the data from the datatable, to return a single object.
Current usage is as follows
using (IUnitOfWork context2 = IocServiceFactory.Resolve<IUnitOfWork>())
{
KpiFormDocumentEntry entry = context2.GetRepository<KpiFormDocumentEntry>().FindById(id, KpiFormDocumentEntry.LoadOptions.FormItem);
And this uses lambda to filter, like so
public static KpiFormDocumentEntry FindById(this IRepository<KpiFormDocumentEntry> source, int id, KpiFormDocumentEntry.LoadOptions loadOptions)
{
return source.Where( qi => qi.Id == id ).LoadWith( loadOptions ).FirstOrDefault();
}
So it becomes a nice extension method.
My Question is, how can I use this same Interface/pattern etc. but also implement IQueryable to properly support LinqToSQL and get some serious performance improvements?
The current implementation/Interfaces for IRepository are as follows
public interface IRepository<T> : IEnumerable<T> where T : class
{
void Add(T entity);
void AddMany(IEnumerable<T> entities);
void Delete(T entity);
void DeleteMany(IEnumerable<T> entities);
IEnumerable<T> All();
IEnumerable<T> Find(Func<T, bool> predicate);
T FindFirst(Func<T, bool> predicate);
}
and then this is implemented by an SqlClientRepository like so
public sealed class SqlClientRepository<T> : IRepository<T> where T : class
{
private readonly Table<T> _source;
internal SqlClientRepository(Table<T> source)
{
if( source == null ) throw new ArgumentNullException( "source", Gratte.Aurora.SHlib.labelText("All_TableIsNull",1) );
_source = source;
}
//removed add delete etc
public IEnumerable<T> All()
{
return _source;
}
public IEnumerator<T> GetEnumerator()
{
return _source.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
The problem at the moment is, in our example above, the .Where is calling 'GetEnumerator', which then loads all rows into memory, and then looks for the one we need.
If I change IRepository to implement IQueryable, I can't implement the three methods needed, as these are not public in the Table class.
I think I should change the SQLClientRepository to be defined like so
public sealed class SqlClientRepository<T> : IQueryable<T>, IRepository<T> where T : class
And then implement the necessary methods, but I can't figure out how to pass the expressions around etc. as they are private members of the Table class, like so
public override Type ElementType
{
get { return _source.ElementType; } //Won't work as ElementType is private
}
public override Expression Expression
{
get { return _source.Expression; } //Won't work as Expression is private
}
public override IQueryProvider Provider
{
get { return _source.Provider; } //Won't work as Provider is private
}
Any help really appreciated to move this from 'iterate through every row in the database after loading it' to 'select x where id=1'!
If you want to expose linq you can stop using the repository pattern and use Linq2Sql directly. The reason to this is that every Linq To Sql provider has it's own custom solutions. So if you expose LINQ you get a leaky abstraction. There is no point in using an abstraction layer then.
Instead of exposing LINQ you got two options:
Implement the specification pattern
Use the repository pattern as I describe here: http://blog.gauffin.org/2013/01/repository-pattern-done-right/
So, while it may not be a true abstraction any longer, the main point was to get the benefit of linq to sql without updating all the queries already written.
so, I made the IRepository implement IQueryable instead of IEnumerable.
then in the SqlClientRepository implementation, I can call AsQueryable() to cast the Table to IQueryable, and then all is good, like so.
Now everywhere somebody has written IRepository().Where(qi => qi.id = id) or similar, it actually passes the ID to sql server and only pulls back one record, instead of all of them, and loops through looking for the correct one.
/// <summary>Provides the ability to query and access entities within a SQL Server data store.</summary>
/// <typeparam name="T">The type of entity in the repository.</typeparam>
public sealed class SqlClientRepository<T> : IRepository<T> where T : class
{
private readonly Table<T> _source;
private readonly IQueryable<T> _sourceQuery;
IQueryable<T> Query()
{
return (IQueryable<T>)_source;
}
public Type ElementType
{
get { return _sourceQuery.GetType(); }
}
public Expression Expression
{
get { return _sourceQuery.Expression; }
}
public IQueryProvider Provider
{
get { return _sourceQuery.Provider; }
}
/// <summary>Initializes a new instance of the <see cref="SqlClientRepository{T}"/> class.</summary>
/// <param name="source">A <see cref="Table{T}"/> to a collection representing the entities from a SQL Server data store.</param>
/// <exception cref="ArgumentNullException"><paramref name="source"/> is a <c>null</c> reference (<c>Nothing</c> in Visual Basic).</exception>
internal SqlClientRepository(Table<T> source)
{
if( source == null ) throw new ArgumentNullException( "source", "All_TableIsNull" ) );
_source = source;
_sourceQuery = _source.AsQueryable();
}
In response to What is your longest-held programming assumption that turned out to be incorrect? question, one of the wrong assumptions was:
That private member variables were
private to the instance and not the
class.
(Link)
I couldn't catch what he's talking about, can anyone explain what is the wrong/right about that with an example?
public class Example {
private int a;
public int getOtherA(Example other) {
return other.a;
}
}
Like this. As you can see private doesn't protect the instance member from being accessed by another instance.
BTW, this is not all bad as long as you are a bit careful.
If private wouldn't work like in the above example, it would be cumbersome to write equals() and other such methods.
Here's the equivalent of Michael Borgwardt's answer for when you are not able to access the private fields of the other object:
public class MutableInteger {
private int value;
// Lots of stuff goes here
public boolean equals(Object o) {
if(!(o instanceof MutableInteger)){ return false; }
MutableInteger other = (MutableInteger) o;
return other.valueEquals(this.value); // <------------
}
#Override // This method would probably also be declared in an interface
public boolean valueEquals(int oValue) {
return this.value == oValue;
}
}
Nowadays this is familiar to Ruby programmers but I have been doing this in Java for a while. I prefer not to rely on access to another object's private fields. Remember that the other object may belong to a subclass, which could store the value in a different object field, or in a file or database etc.
Example code (Java):
public class MutableInteger {
private int value;
// Lots of stuff goes here
public boolean equals(Object o) {
if(!(o instanceof MutableInteger)){ return false; }
MutableInteger other = (MutableInteger) o;
return this.value == other.value; // <------------
}
}
If the assumption "private member variables are private to the instance" were correct, the marked line would cause a compiler error, because the other.value field is private and part of a different object than the one whose equals() method is being called.
But since in Java (and most other languages that have the visibility concept) private visibility is per-class, access to the field is allowed to all code of the MutableInteger, irrelevant of what instance was used to invoke it.