Is it ok to get/set session variable inside a private/public property?
private List<FileAttachment> fileAttachments;
public List<FileAttachment> FileAttachments
{
get
{
if (Session["key"] != null)
{
fileAttachments = (List<FileAttachment>)Session["key"];
}
return fileAttachments;
}
set
{
fileAttachments = value;
Session["key"] = fileAttachments;
}
}
The goal here is I'd like for the container class (of this user control the property is in) to be able to set the List<T> depending on what entity and show existing attachments that's stored in the database.
That's not very safe; List<T> is not thread-safe.
You can never modify the list after assigning it to the property, since some other request thread might be reading it.
Therefore, you should make it a ReadOnlyCollection<T> rather than List<T>.
(and make sure your FileAttachment class is immutable or thread-safe)
Other than that, it depends where the property is.
If it's on a control or page, it's fine.
Related
I'm making a simple Search page in MVC with some filters in it. The filters are represented by properties in my ViewModel. My ViewModel is binded to a GET form in the cshtml so my filter will appears in the querystrings and the user will be able to bookmark his search.
What I want to do is to assign a default value to some of my filters.
My (simplified) ViewModel :
public class SearchViewModel
{
//Filter I want to set a default value to
public OrganizationType? OrganizationType {get; set;}
//Results of the search
public IEnumerable<ItemViewModel> Items {get; set;}
}
I'd like to set a default value for OrganizationType. I can't simply set it in the constructor of SearchViewModel because it depends on the current user :
public void InitViewModel(SearchViewModel vm)
{
vm.OrganizationType = _someLogic.GetDefaultValue(_currentUser);
}
First solution was simply to check if OrganizationType is null, then assign a default value :
public ActionResult Search(SearchViewModel vm)
{
if(vm.OrganizationType == null)
vm.OrganizationType = _someLogic.GetDefaultValue(_currentUser);
return View(vm);
}
But this solution doesn't work as a null value corresponds to an empty filter and it's a choice that the user can make. So I can't override it.
The second solution I tried was to specify that the default value of the controller should be null in the Search action :
public ActionResult Search(SearchViewModel vm = null)
{
if (vm == null)
{
vm = new SearchViewModel();
InitViewModel(vm);
}
...
return View(vm);
}
But in practice, the variable vm is never null, so the default values are never setted.
I also tried having two Action, one wihout a ViewModel where I instanciate a new ViewModel with the default values and then call the second action :
public ActionResult Search()
{
var vm = new SearchViewModel();
InitViewModel(vm);
//Simply call the second action with the initizalied ViewModel
return Search(vm);
}
public ActionResult Search(SearchViewModel vm)
{
...
return View(vm);
}
But it doesn't work because there is now an ambiguity between the two action, and asp.net doesn't know which one to choose.
So in summary, I'd like to find a way to set a default value for a ViewModel, without setting it in the constructor and overriding user choices.
Another way to say it, how can I distinguish an "empty" ViewModel from one where some values are binded from the form.
Any idea ?
Ok I think I found a solution to my own problem...
I can use the ModelState property of the controler to check it the ViewModel is empty or was binded from the form :
public ActionResult Search(SearchViewModel vm = null)
{
if (ModelState.Count == 0)
{
InitViewModel(vm);
}
...
return View(vm);
}
So if ModelState.Count equals to 0 it means that user didn't change any filters. So the form is empty and we can bind our default values. As soon as the user will change one of the filters or submit the request, the ModelState.Count will be greater than 0 so we shouldn't set the default value. Otherwise we would override an user choice.
The logic of what you're doing is a little iffy. Generally speaking, if a value is nullable then null is the default value. However, it seems that you're trying to make a distinction here between whether the value is null because it's not set or null because the user explicitly set it to null. This type of semantic variance is usually a bad idea. If null has a meaning, then it should always carry that meaning. Otherwise, your code becomes more confusing and bugs are generally introduced as a result.
That said, you can't count on ModelState having no items. I've honestly never played around with ModelState enough in scenarios where there's not post data, but it's possible there's some scenario where there's no post data and yet ModelState may have items. Even if there isn't, this is an implementation detail. What if Microsoft does an update that adds items to ModelState in situations where it previously had none. Then, your code breaks with no obvious reason why.
The only thing you can really count on here is whether the request method is GET or POST. In the GET version of your action, you can reasonably assume that the user has made no modifications. Therefore, in this scenario, you can simply set the value to whatever you like without concern.
In the POST version of your action, the user has made some sort of modification. However, at this point, there is no way to distinguish any more whether the value is null because it is or because the user explicitly wanted it to be. Therefore, you must respect the value as-is.
I have a ViewModel that contains a (Person)Patient property. In my View, I bind to some of the properties of Patient, say, Name and Age.
The problem is: if I change Patient, nothing happens in my view, unless I explicitly notify of each property change (I am using Caliburn.Micro thus the PropertyChangedBaseand NotifyOfPropertyChange stuff):
public class PersonViewModel : PropertyChangedBase {
Person _patient;
public Person Patient {
get { return _patient; }
set {
_patient = value;
NotifyOfPropertyChange(() => Patient); // this doesn't update the view
NotifyOfPropertyChange(() => Name); // this updates, but would I need one line for each property??
}
}
}
The broader application context is this: I have a PersonManager screen, with three regions, each with their view and viewmodel: a list of persons, the information of a single person, and the list of medical procedures associated with each person.
I am almost sure I am missing something here. I would like to select a person in the person list, and then the regions showing person data and person procedures would update via binding, without having to manually notify each property change of the newly selected person.
I have solved the problem using a feature of PropertyChanged event, which is using null as a parameter:
The PropertyChanged event can indicate all properties on the object
have changed by using either null or String.Empty as the property name
in the PropertyChangedEventArgs.
Then, I solved my problem with:
public Paciente Paciente {
get { return _paciente; }
set {
_paciente = value;
NotifyOfPropertyChange(null);
}
}
and it worked!
I am very confused with properties in asp.net.
I just don't understand why we use properties and when I should use them. Could anybody elaborate a little on this.
public class Customer
{
private int m_id = -1;
public int ID
{
set
{
m_id = value;
}
}
private string m_name = string.Empty;
public string Name
{
set
{
m_name = value;
}
}
public void DisplayCustomerData()
{
Console.WriteLine("ID: {0}, Name: {1}", m_id, m_name);
}
}
Properties provide the opportunity to protect a field in a class by reading and writing to it through the property. In other languages, this is often accomplished by programs implementing specialized getter and setter methods. C# properties enable this type of protection while also letting you access the property just like it was a field.
Another benefit of properties over fields is that you can change their internal implementation over time. With a public field, the underlying data type must always be the same because calling code depends on the field being the same. However, with a property, you can change the implementation. For example, if a customer has an ID that is originally stored as an int, you might have a requirements change that made you perform a validation to ensure that calling code could never set the ID to a negative value. If it was a field, you would never be able to do this, but a property allows you to make such a change without breaking code. Now, lets see how to use properties.
Taken From CSharp-Station
There are a couple of good reasons for it. The first is that you might need to add validation logic in your setter, or actually calculate the value in the getter.
Another reason is something to do with the IL code generated. If you are working on a large project that is spread over multiple assemblies then you can change the code behind your property without the application that uses your assembly having to recompile. This is because the "access point" of the property stays the same while allowing the implementation code behind it to be altered. I first read about this when I was looking into the point of automatic properties as I didnt see the point between those and a normal public variable.
It's easy.
All fields in class MUST be private (or protected). To show fields to another class yyou can use properties or get/set methods. Properties a shorter.
P.S. Don't declare write-only properties. It is worst practices.
Properties are a convenient way to encapsulate your classes' data.
Quoting from MSDN:
A property is a member that provides a flexible mechanism to read,
write, or compute the value of a private field. Properties can be used
as if they are public data members, but they are actually special
methods called accessors. This enables data to be accessed easily and
still helps promote the safety and flexibility of methods.
Let's consider two common scenarios:
1) You want to expose the Name property without making it changeable from outside the class:
private string m_name = string.Empty;
public string Name
{
get
{
return m_name;
}
}
2) You want to perform some checks, or run some code every time the data is accessed or set:
private string m_name = string.Empty;
public string Name
{
get
{
return m_name;
}
set
{
m_name = (String.IsNullOrEmpty(value)) ? "DefaultName" : value;
}
}
see:
http://msdn.microsoft.com/en-us/library/x9fsa0sw.aspx
The most important reason is for validation purpose in setter and manipulation part can be implemented in get part.
For Ex.
Storing weekdays, which should be from 1-7, if we take normal variable and declare it as public, anyone can assign any value.
But in Properties setter you can control and validate.
The next one you can use it for tracking. That means, you can know how many times set and get functions has been called by clients (statistical purpose, may be not useful frequently).
Finally, you can control read only, write only and read/write for the properties according to your requirements.
Pardon me if this question has already been asked. HttpContext.Current.Session["key"] returns an object and we would have to cast it to that particular Type before we could use it. I was looking at various implementations of typed sessions
http://www.codeproject.com/KB/aspnet/typedsessionstate.aspx
http://weblogs.asp.net/cstewart/archive/2008/01/09/strongly-typed-session-in-asp-net.aspx
http://geekswithblogs.net/dlussier/archive/2007/12/24/117961.aspx
and I felt that we needed to add some more code (correct me if I was wrong) to the SessionManager if we wanted to add a new Type of object into session, either as a method or as a separate wrapper. I thought we could use generics
public static class SessionManager<T> where T:class
{
public void SetSession(string key,object objToStore)
{
HttpContext.Current.Session[key] = objToStore;
}
public T GetSession(string key)
{
return HttpContext.Current.Session[key] as T;
}
}
Is there any inherent advantage in
using
SessionManager<ClassType>.GetSession("sessionString")
than using
HttpContext.Current.Session["sessionString"] as ClassType
I was also thinking it would be nice
to have something like
SessionManager["sessionString"] = objToStoreInSession,
but found that a static class cannot have an indexer. Is there any other way to achieve this ?
My thought was create a SessionObject which would store the Type and the object, then add this object to Session (using a SessionManager), with the key. When retrieving, cast all objects to SessionObject ,get the type (say t) and the Object (say obj) and cast obj as t and return it.
public class SessionObject { public Type type {get;set;} public Object obj{get;set;} }
this would not work as well (as the return signature would be the same, but the return types will be different).
Is there any other elegant way of saving/retrieving objects in session in a more type safe way
For a very clean, maintainable, and slick way of dealing with Session, look at this post. You'll be surprised how simple it can be.
A downside of the technique is that consuming code needs to be aware of what keys to use for storage and retrieval. This can be error prone, as the key needs to be exactly correct, or else you risk storing in the wrong place, or getting a null value back.
I actually use the strong-typed variation, since I know what I need to have in the session, and can thus set up the wrapping class to suit. I've rather have the extra code in the session class, and not have to worry about the key strings anywhere else.
You can simply use a singleton pattern for your session object. That way you can model your entire session from a single composite structure object. This post refers to what I'm talking about and discusses the Session object as a weakly typed object: http://allthingscs.blogspot.com/2011/03/documenting-software-architectural.html
Actually, if you were looking to type objects, place the type at the method level like:
public T GetValue<T>(string sessionKey)
{
}
Class level is more if you have the same object in session, but session can expand to multiple types. I don't know that I would worry about controlling the session; I would just let it do what it's done for a while, and simply provide a means to extract and save information in a more strongly-typed fashion (at least to the consumer).
Yes, indexes wouldn't work; you could create it as an instance instead, and make it static by:
public class SessionManager
{
private static SessionManager _instance = null;
public static SessionManager Create()
{
if (_instance != null)
return _instance;
//Should use a lock when creating the instance
//create object for _instance
return _instance;
}
public object this[string key] { get { .. } }
}
And so this is the static factory implementation, but it also maintains a single point of contact via a static reference to the session manager class internally. Each method in sessionmanager could wrap the existing ASP.NET session, or use your own internal storage.
I posted a solution on the StackOverflow question is it a good idea to create an enum for the key names of session values?
I think it is really slick and contains very little code to make it happen. It needs .NET 4.5 to be the slickest, but is still possible with older versions.
It allows:
int myInt = SessionVars.MyInt;
SessionVars.MyInt = 3;
to work exactly like:
int myInt = (int)Session["MyInt"];
Session["MyInt"] = 3;
i have a HttpModule that creates an CommunityPrincipal (implements IPrincipal interface) object on every request. I want to somehow store the object for every request soo i can get it whenever i need it without having to do a cast or create it again.
Basically i want to mimic the way the FormsAuthenticationModule works.
It assigns the HttpContext.User property an object which implements the IPrincipal interface, on every request.
I somehow want to be able to call etc. HttpContext.MySpecialUser (or MySpecialContext.MySpecialUser - could create static class) which will return my object (the specific type).
I could use a extension method but i dont know how to store the object so it can be accessed during the request.
How can this be achieved ?
Please notice i want to store it as the specific type (CommunityPrincipal - not just as an object).
It should of course only be available for the current request being processed and not shared with all other threads/requests.
Right now i assign my CommunityPrincipal object to the HttpContext.User in the HttpModule, but it requires me to do a cast everytime i need to use properties on the CommunityPrincipal object which isnt defined in the IPrincipal interface.
I'd recommend you stay away from coupling your data to the thread itself. You have no control over how asp.net uses threads now or in the future.
The data is very much tied to the request context so it should be defined, live, and die along with the context. That is just the right place to put it, and instantiating the object in an HttpModule is also appropriate.
The cast really shouldn't be much of a problem, but if you want to get away from that I'd highly recommend an extension method for HttpContext for this... this is exactly the kind of situation that extension methods are designed to handle.
Here is how I'd implement it:
Create a static class to put the extension method:
public static class ContextExtensions
{
public static CommunityPrinciple GetCommunityPrinciple(this HttpContext context)
{
if(HttpContext.Current.Items["CommunityPrinciple"] != null)
{
return HttpContext.Current.Items["CommunityPrinciple"] as CommunityPrinciple;
}
}
}
In your HttpModule just put the principal into the context items collection like:
HttpContext.Current.Items.Add("CommunityPrincipal", MyCommunityPrincipal);
This keeps the regular context's user property in the natural state so that 3rd party code, framework code, and anything else you write isn't at risk from you having tampered with the normal IPrincipal stroed there. The instance exists only during the user's request for which it is valid. And best of all, the method is available to code as if it were just any regular HttpContext member.... and no cast needed.
Assigning your custom principal to Context.User is correct. Hopefully you're doing it in Application_AuthenticateRequest.
Coming to your question, do you only access the user object from ASPX pages? If so you could implement a custom base page that contains the cast for you.
public class CommunityBasePage : Page
{
new CommunityPrincipal User
{
get { return base.User as CommunityPrincipal; }
}
}
Then make your pages inherit from CommunityBasePage and you'll be able to get to all your properties from this.User.
Since you already storing the object in the HttpContext.User property all you really need to acheive you goal is a Static method that acheives your goal:-
public static class MySpecialContext
{
public static CommunityPrinciple Community
{
get
{
return (CommunityPrinciple)HttpContext.Current.User;
}
}
}
Now you can get the CommunityPrinciple as:-
var x = MySpecialContext.Community;
However it seems a lot of effort to got to avoid:-
var x = (CommunityPrinciple)Context.User;
An alternative would be an Extension method on HttpContext:-
public static class HttpContextExtensions
{
public static CommunityPrinciple GetCommunity(this HttpContext o)
{
return (CommunityPrinciple)o.User;
}
}
The use it:-
var x = Context.GetCommunity();
That's quite tidy but will require you to remember to include the namespace where the extensions class is defined in the using list in each file the needs it.
Edit:
Lets assume for the moment that you have some really good reason why even a cast performed inside called code as above is still unacceptable (BTW, I'd be really interested to understand what circumstance leads you to this conclusion).
Yet another alternative is a ThreadStatic field:-
public class MyModule : IHttpModule
{
[ThreadStatic]
private static CommunityPrinciple _threadCommunity;
public static CommunityPrinciple Community
{
get
{
return _threadCommunity;
}
}
// Place here your original module code but instead of (or as well as) assigning
// the Context.User store in _threadCommunity.
// Also at the appropriate point in the request lifecyle null the _threadCommunity
}
A field decorated with [ThreadStatic] will have one instance of storage per thread. Hence multiple threads can modify and read _threadCommunity but each will operate on their specific instance of the field.