I have an User model:
class User: Object, Mappable {
dynamic var account: String?
dynamic var balabala
static var current: User {
return realm.objects(User.self) ?? User()
}
}
But it throws an error: Instance member 'realm' cannot be used on type 'User'
How to use singleton with realm object?
Any help is appreciated
Your User class doesn't define an instance variable called realm, so in your current property the Swift compiler doesn't know what realm refers to.
If you just want to use the default Realm, you need to initialize a new instance of it:
try! Realm().objects(User.self)
Otherwise, as Kam referred to in the comments, set up a separate class for managing your singleton Realm and get the Realm from that class instead.
Related
I am developing a backend with nestjs + mongoose.
As nestjs document suggests, I wrote mongoose schema class following
(this schema has GraphQL decorators , #Prop is mongoose decorator )
#Schema({
timestamps: true,
})
#ObjectType()
#InputType('UserInput')
export class User extends BaseModel {
#Prop()
#Field()
email: string;
#Prop()
#Field({ nullable: true })
username?: string;
...
then in user service layer
async loginUser(loginDto: LoginDto) {
let user: User | undefined = await this.userRepository.findUser(loginDto);
if (!user) {
user = await this.userRepository.createUser(loginDto);
}
I use User object type that user repository returns. this must be same with User Schema that I defined for mongoose with Class.
I think the User Class and user instance ( let user: User | undefined ) returned from userRepositry.findUser violate OOP since the instance can access to all the properties since those properties are public due to use of decorators.
I think I have seen an article that nestjs can't resolve decorators used with private properties inside Class and Nestjs document also doesn't set schema class properties to private . so I didn't set properties in my schema classes to private either
what I doubt about this code is wether I need to create User object which is irrelevant to Schema Class but has same properties in private and instantiate it in service layer for business logic in OOP perspective or not. I think DTO and DAO might be for this use case ? if so , Should I strictly create DTO and DAO in this case ? or ..if there is another way to keep OOP with nestjs and decorators
Hey Guys i'm very new in software development,I still no idea when to use which,whats the meaning of service lifetime!it may seem stupid but please help me,i have an interface :
public interface IAccessInfo
{
public IEnumerable<AccessInfo> getResult();
}
what it supposed to do is to returns me the information about my Turbines;here is the implementation of it :
public class AcessInfoData:IAccessInfo
{
private DbContextClass db;
public AcessInfoData(DbContextClass context)
{
db = context;
}
public IEnumerable<AccessInfo> getResult()
{
var turbines = (from c in db.accessinf
where s.user_id == "i0004912"
select new AccessInfo
{
InfoType = c.type,
TurbineId = c.m_plc_id.ToString(),
TurbineIP = c.turbine_ip.ToString(),
TurbineIdSorting = c.turbine_id,
Blade = c.blade,
Certification = c.certification,
}).Distinct();
return turbines;
}
}
it gets an instance of my DB and gets the data;and in my controller i use it like this:
public class AcessInfoController : ControllerBase
{
private IAccessInfo _acess;
public AcessInfoController(IAccessInfo access)
{
_acess = access;
}
[HttpGet]
public IActionResult Index()
{
var rsult = _acess.getResult();
return Ok( rsult);
}
}
now in the Startup i registered it :
services.AddScoped<IAccessInfo, AcessInfoData>();
it works,but if you sk me why i user Scoped and not Singleton or transient i have no idea why,really,any one can make it clear for me?
I will try to explain a little about the mentioned cases:
scoped : For all needs of an object during the life of an operation (such as a request from the client) a single instance of the object is created. (It means that only one instance of the object is sent for all requirements during life time of a request)
Singleton: Creates only one instance of object and sends it for all requirements in the application scope.(For all needs everywhere in the program, only one instance of the object is sent, a bit like static objects).
Transient: Ioc container, makes an instance of object whenever code needs it, that is, it makes an instance for each requirement anywhere in the program and at any time, which means that if the program needs an object 3 times, it makes an independent instance for each.
Instance: In this case, each time an object is needed, only one instance of it is provided to the program, which you defined it in the startup section. (when defining it in the startup section, you specify how to create an instance).
I hope to reduce some of the ambiguities.
I've an abstract class:
[Configuration]
public abstract class AbstractAddon : IAddon
{
private readonly object configuration;
public AbstractAddon(object configuration)
{
this.configuration = configuration;
}
}
And several implementation of this.
I create a binding by convention as:
public class AddonsModule : Ninject.Modules.NinjectModule
{
public override void Load()
{
this.Bind(b => b.FromAssembliesMatching("*")
.SelectAllClasses()
.InheritedFrom(typeof(UIExtensibility.AbstractAddon))
.BindAllBaseClasses()
.Configure(c => c.InSingletonScope())
);
this.Bind<object>().ToProvider<ConfigurationProvider>().WhenClassHas<UIExtensibility.ConfigurationAttribute>();
}
and ConfigurationProvider is:
private class ConfigurationProvider : IProvider<object>
{
public object Create(IContext context)
{
return "configuration settings";
}
//...
}
Inside the Create method of ConfigurationProvider I thought I might be allowed to access which is the concrete class which is being requested around.
Each concrete class have an attribute PluginInformation I need in order to provide the correct configuration object. However, I don't know how to know which is the concrete class NInject is creating at the moment of the Create method provider is performed. And then, I can't get the PluginInformation attribute I need to link it and provide the correct configuration object.
How could I get access to the concrete class NInject is requesting at the moment of the object provider is performed?
The trouble was that on the first level of the IContext context parameter information, there is only the information according the Type it's providing, in my case: object type.
However IContext comes with the complete parent and plan context. So, at the point of the Create method of the provider is performed, some braches of the resolution are solved, for example: AbstractAddon. Every resolved information is on 'Context' like IContext fields. Moreover, the future steps are on 'Plan' like IContext fields.
So, in order to get the concrete type (inherited classes of AbstractAddon), I need to read the next property: context.Request.ParentContext.Plan.Type.
I am looking for some help creating an implementation of IScopeAccessor, or finding a new solution, that will allow me to provide an NHibernate session per ViewModel.
I know that Windsor now supports scoped lifestyles as seen (here). However the example creates the special scope with a using block and calling container.resolve within the using.
_container.Register(Component.For<A>().LifestyleScoped());
using (_container.BeginScope())
{
var a1 = _container.Resolve<A>();
var a2 = _container.Resolve<A>();
Assert.AreSame(a1, a2);
}
I can't think of a way to make this work because I don't want to pass around the container and I want the scope to be tied to the ViewModel that gets created, which will happen dynamically as they are needed.
As an alternative it looks like I can create an implementation of IScopeAccessor which, according to Krzysztof Koźmic (here) would allow me to
"... provide any scope you like. Scope is an abstract term here and it can be anything."
Unfortunately I cannot find an implementation of IScopeAccessor that isn't specific to a web based scenario and I am struggling to understand exactly what I need to do to turn "anything" into a valid scope.
I have found an example of exactly what I want to do using Ninject (http://www.emidee.net/index.php/2010/08/23/ninject-use-one-database-session-per-view-model/):
Bind<ISession>().ToMethod(ctx =>
{
var session = ctx.Kernel.Get<....>().BuildSessionFactory().OpenSession();
return session;
})
.InScope(context =>
{
var request = context.Request;
if (typeof(IViewModel).IsAssignableFrom(request.Service))
return request;
while ((request = request.ParentRequest) != null)
if (typeof(IViewModel).IsAssignableFrom(request.Service))
return request;
return new object();
});
In Ninject, the InScope indicates that any instances created by the binding should be reused as long as the object returned by the call back remains alive. Essentially, this call back returns the root level ViewModel (since ViewModels can be nested).
Any thoughts on how I can do the same thing or get the same result using Windsor?
The problem seems to be the place of creation.
If it's all about dependencies of viewmodels being constructed, you could maybe use boud lifestyle, as described in What's new...
Or you could alternatively use your own scope accessor, that is sensitive to viewmodels. for example like this:
public class ViewModelScopeAccessor : IScopeAccessor
{
private IDictionary<Guid, ILifetimeScope> scopes = new Dictionary<Guid, ILifetimeScope>();
private ILifetimeScope defaultScope;
public ViewModelScopeAccessor()
: this(new DefaultLifetimeScope())
{ }
public ViewModelScopeAccessor(ILifetimeScope defaultScope)
{
this.defaultScope = defaultScope;
}
public ILifetimeScope GetScope(CreationContext context)
{
var creator = context.Handler.ComponentModel.Implementation;
var viewModel = creator as IViewModel;
if (viewModel != null)
{
ILifetimeScope scope;
if (!scopes.TryGetValue(viewModel.UID, out scope))
{
scope = new DefaultLifetimeScope();
scopes[viewModel.UID] = scope;
}
return scope;
}
else
{
return defaultScope;
}
}
public void Dispose()
{
foreach (var scope in scopes)
{
scope.Value.Dispose();
}
defaultScope.Dispose();
scopes.Clear();
}
}
for the following viewmodel interface :
public interface IViewModel
{
string DisplayName { get; }
Guid UID { get; }
}
You of course could compare the viewmodels in other ways, it's just an example.
The drawback of both, the bound lifestyle and that scope accessor, is, that it won't work, if you use a typed factory inside your viewmodel, to lazily construct objects, since the scope accessor has no idea, from which object/method its factory method was called. But I think is is a general .NET issue, since a method does actually never know, from where it has been called.
So, you could then use your own factories, that produce only one instance per factory instance and make them scoped to your viewmodels too.
Hope this helps.
for some reason I don't wanna let user to create an instance of the object, without sending a property to the constructor
but as I know the object should have default constructor and so it would be possible to create an instance with out sending requierd property.
is there any way to prevent this problem? and if yes does it have any side effect?
Just use a protected default constructor:
public class Product
{
protected Product() { }
public Product(Category category)
{
this.Category = category;
}
}
"NHibernate allows a private default constructor for Value Objects, but for Entities you will need a default public or protected constructor as private is not sufficient."
Here you can find something:
https://github.com/davybrion/companysite-dotnet/blob/master/content/blog/2009-10-why-nhibernate-entities-need-a-public-or-protected-parameterless-constructor.md
Here there's an experiment to work without constructor:
http://kozmic.net/2011/03/20/working-with-nhibernate-without-default-constructors/
This is an example working with Dependency Injection:
http://nhibernate.info/blog/2008/12/12/entities-behavior-injection.html