Maintaining Connection Strings Across Modules in a WPF MVVM Pattern

Question

I have a WPF application using MVVM with Prism and Unity.  My loging screen obtains connection strings from the module's app.config and puts them into a combox so that the user can select the connection .  I need to persist the string so that it is discoverable by Views that are injected into the main screen.  From my reading, I THINK that I have learned that using a Singleton is the best way to accomplish this, but I am not sure.  I have read about Singletons in an abstract sense, but I don't have a handle on how it would be used to accomplish my specific goal.  So I have these questions: 1) Is a Singleton the best way to persist a string value across injected views/view modes?; 2) If not, then what?; 3) Can you point me to an example that is solves a problem similar to the one I have presented?

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REvans

Answer 1

Hello,

You should post this question to a more related forum like a WPF forum, because this good really nothing to do with SQL Server Data Access.

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Olaf Helper
* cogito ergo sum * errare humanum est * quote erat demonstrandum *
Wenn ich denke, ist das ein Fehler und das beweise ich täglich
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Answer 2

I think it has more to do with general .NET since there are no global values in C#, but I asked a similar question in the Prism forum and was told that since it related to SQL Server, I should post it here.

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REvans

Answer 3

Why don't you save the connection string in the application settings, it's easy to use and to maintain, if e.g. the server name changes?

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Olaf Helper
* cogito ergo sum * errare humanum est * quote erat demonstrandum *
Wenn ich denke, ist das ein Fehler und das beweise ich täglich
Blog Xing

Answer 4

Hello REvans611,

I am surprised by what you have written "there are no global values in C#". It is false : it is called static in VC# and Shared in VB. You have only to declare in a class with a public attribute.

You should see :

for C# : http://msdn.microsoft.com/en-us/library/98f28cdx.aspx

for VB : http://msdn.microsoft.com/en-us/library/zc2b427x.aspx

I gave the link towards VB as it could be useful for developers in VB ( i think it is not the 1st time that your question is asked in this forum )

About to save the connection string in the application settings , i am absolutely against : it is too easy to see this connection string , to modify/hijack it.It is breaking a basic rule : to avoid to show a connection string.

For myself, i am always using a connection form a little like the connection form used to connect in the SQL Server Management Studio (SSMS). I fill a listbox of available SQL Server instances with a call to the SqlDataSourceEnumerator class..

http://msdn.microsoft.com/en-us/library/system.data.sql.sqldatasourceenumerator(VS.90).aspx

http://msdn.microsoft.com/en-us/library/system.data.sql.sqldatasourceenumerator.getdatasources(VS.90).aspx

http://msdn.microsoft.com/en-us/library/a6t1z9x2(VS.90).aspx

2 advices :

- for some editions of SQL Server ( mainly Express ), a single call to GetDataSources() is not enough, it is why in my programs, i code twice this call

- check whether the Version column is not set to empty or null.Usually, it means that the related SQL Server Service is not running.

For myself, i prefer to use http://msdn.microsoft.com/en-us/library/ms210350(SQL.100).aspx ( surely because i am mainly writing programs needing SMO ). The returned datatable is more "complete" ( with especially the IsClustered and Locale columns ). Moreover, it seems ( according my own experience ) that the returned datable contains usually more rows with EnumAvailableSqlServers than with GetDataSources, but the SMO code is slower and i am not sure that WPF is authorizing the call to SMO classes ( maybe a problem with .Net Framework 2.0 )

Have a nice day

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Mark Post as helpful if it provides any help.Otherwise,leave it as it is.

Answer 5

I am surprised by what you have written "there are no global values in C#". It is false

Hello Papy,

I hope you enjoyed your vacation.

He didn't wrote about a "value", he mean a "global variable". In VB.NET you can define a global variable and you can use/access it in every class

Public Modul TestModul

    Public MyGlobalVar as String = "Hello World"

End Modul

But this is an old relict from VB 6.0 version. Internal .NET map this to a shared class with a static variable.

In C# (as well as VB.NET) you can use a Singleton (from patter&pratice group) to accomplish the same behaviour. See also Implementing Singleton in C#

And why not storing a connection string into appilcation settings, you can easily decryt/encryt it.

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Olaf Helper
* cogito ergo sum * errare humanum est * quote erat demonstrandum *
Wenn ich denke, ist das ein Fehler und das beweise ich täglich
Blog Xing

Answer 6

Hmmm.  Seems like you have to have a global variable in order to have a global value.  I have read various posts saying that there are no global values in C# while suggesting a look into a static variable.  Maybe this is just an inadvertant exercise in symantics, and maybe I am confusing myself by overthinking this because of the MVVM/Prism/Unity context.  I will follow the suggested links and experiment with a static variable and a singleton and report back my findings when I am successful.  Maybe it will help some other forum searchers.  Thank you, all.  I am very appreciative of your input.

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REvans