Is this possible? 'Dynamic' Code

[jdn]

I have a class called myConfigurationClass with 3 private members, and 3 public gets (so, 3 read-only properties). So, for instance

private members: _A, _B, _
public gets A, B,

Oh, and they are all strings. In particular, they are Connection strings for SQL Server

In my web config, I have an appSetting, let's call it "CurrentConnectionString", and its value is either "A", "B", or "C

How can you write code so that it reads the value of "CurrentConnectionString" and then executes the proper get

The typical way would be something like

Step 1) create a string to hold the value of the key

Step 2) using either case or if-else if-else, loop through and see what the value is, and do other stuff accordingl

Thus

System.Configuration.AppSettingsReader AppSettingsReader = new System.Configuration.AppSettingsReader()
string ConnectionStringType = (string)AppSettingsReader.GetValue("CurrentConnect ionString", typeof(string))
string ConnectionString = ""
if (ConnectionString == "A"

ConnectionString = myConfigurationClass.A

else if (ConnectionString == "B"

ConnectionString = myConfigurationClass.B

els

ConnectionString = myConfigurationClass.

Is there a way that I could dump the if - else stuff and write something like

string ConnectionString = myConfigurationClass.[ConnectionStringType]; //which doesn't wor

where it 'dynamically' writes the code that follows "myConfigurationClass.

TI

jdn

[Scott M.]

Why not have one property that may return one of 3 values instead of 3
properties and needing to find out which you want?
"jdn" <ki******@earthlink.net> wrote in message
news:A5**********************************@microsof t.com...

I have a class called myConfigurationClass with 3 private members, and 3 public gets (so, 3 read-only properties). So, for instance:
private members: _A, _B, _C
public gets A, B, C

Oh, and they are all strings. In particular, they are Connection strings for SQL Server.
In my web config, I have an appSetting, let's call it "CurrentConnectionString", and its value is either "A", "B", or "C"
How can you write code so that it reads the value of "CurrentConnectionString" and then executes the proper get?
The typical way would be something like:

Step 1) create a string to hold the value of the key.

Step 2) using either case or if-else if-else, loop through and see what the value is, and do other stuff accordingly
Thus:

System.Configuration.AppSettingsReader AppSettingsReader = new System.Configuration.AppSettingsReader(); string ConnectionStringType = (string)AppSettingsReader.GetValue("CurrentConnect ionString",
typeof(string)); string ConnectionString = "";
if (ConnectionString == "A")
{
ConnectionString = myConfigurationClass.A;
}
else if (ConnectionString == "B")
{
ConnectionString = myConfigurationClass.B;
}
else
{
ConnectionString = myConfigurationClass.C
}

Is there a way that I could dump the if - else stuff and write something like:
string ConnectionString = myConfigurationClass.[ConnectionStringType]; //which doesn't work
where it 'dynamically' writes the code that follows "myConfigurationClass."
TIA

jdn

[Philip Rieck]

Normally, when people think they need to do this, they haven't looked for
better alternatives or designs. However, you're right that sometimes its
the best way, and it's never bad to know the options, so.... You can do what
you are asking using Reflection:
using System.Reflection;
....
Type ccType = myConfigurationInst.GetType();
string val = (string)ccType.InvokeMember( "A", BindingFlags.Public |
BindingFlags.GetProperty | BindingFlags.Instance, null, myConfigurationInst,
new object[] {/*args would go here*/});
This will do (slowly) the same thing as calling the property get like so:
string val = myConfigurationInst.A;

*please not that this was posted without a compiler handy, so you may need
to correct my enum / spelling memory before this would compile! The basic
concept here is to call Type.InvokeMember on the type of your object.


"jdn" <ki******@earthlink.net> wrote in message
news:54**********************************@microsof t.com...

Well, there are different scenarios where what I am asking about would be important (though there certainly is more than one way to skin a cat, as you
point out), so I'd like to know if it is possible.
Thanks.

----- Scott M. wrote: -----

Why not have one property that may return one of 3 values instead of 3 properties and needing to find out which you want?
"jdn" <ki******@earthlink.net> wrote in message
news:A5**********************************@microsof t.com...

> I have a class called myConfigurationClass with 3 private members, and 3

public gets (so, 3 read-only properties). So, for instance: >> private members: _A, _B, _C > public gets A, B, C

>> Oh, and they are all strings. In particular, they are Connection

strings for SQL Server. >> In my web config, I have an appSetting, let's call it "CurrentConnectionString", and its value is either "A", "B", or "C" >> How can you write code so that it reads the value of "CurrentConnectionString" and then executes the proper get? >> The typical way would be something like:
>> Step 1) create a string to hold the value of the key.
>> Step 2) using either case or if-else if-else, loop through and see

what

the value is, and do other stuff accordingly >> Thus:
>> System.Configuration.AppSettingsReader AppSettingsReader = new System.Configuration.AppSettingsReader();

> string ConnectionStringType = (string)AppSettingsReader.GetValue("CurrentConnect ionString",
typeof(string));

> string ConnectionString = "";
> if (ConnectionString == "A")
> {
> ConnectionString = myConfigurationClass.A;
> }
> else if (ConnectionString == "B")
> {
> ConnectionString = myConfigurationClass.B;
> }
> else
> {
> ConnectionString = myConfigurationClass.C
> }

>>>> Is there a way that I could dump the if - else stuff and write

something like: >> string ConnectionString =

myConfigurationClass.[ConnectionStringType];

//which doesn't work >> where it 'dynamically' writes the code that follows "myConfigurationClass." >> TIA
>> jdn

[jdn]

----- Philip Rieck wrote: -----

Normally, when people think they need to do this, they haven't looked for
better alternatives or designs. However, you're right that sometimes its
the best way, and it's never bad to know the options, so.... You can do what
you are asking using Reflection:
using System.Reflection;
....
Type ccType = myConfigurationInst.GetType();
string val = (string)ccType.InvokeMember( "A", BindingFlags.Public |
BindingFlags.GetProperty | BindingFlags.Instance, null, myConfigurationInst,
new object[] {/*args would go here*/});
This will do (slowly) the same thing as calling the property get like so:
string val = myConfigurationInst.A;

*please not that this was posted without a compiler handy, so you may need
to correct my enum / spelling memory before this would compile! The basic
concept here is to call Type.InvokeMember on the type of your object.
Thanks.

jdn

[Nels Olsen]

Solve this using the Abstract Factory design pattern. See "Design Patterns" by the "Gang of Four" -- Gamma, Helm, Johnson, Vlissides. Buy this book if you don't already have it. It was written in 1994, inspired by Christopher Alexander's 1977 "A Pattern Language: Towns/Buildings/Construction", and actual code examples are C++, but it is a timeless classic that covers the basics of OOAD. It is well organized and to the point -- you will be able to refer back to it quickly.

First, define a base class (say ConfigurationBase) with just one property, ConnectString. Then create three subclasses, AConfiguration, BConfiguration, and CConfiguration, each of which has its own straightforward logic to return its specific connect string through the ConnectString property. Note that "A", "B" and "C" can be fixed symbols (say Development, Test and Production), while the actual returned by the ConnectString property is their actual implemented value (e.g. "dsn=TheDevelServer;uid=TheDevelDb;...")

Finally, create a factory class (say ConfigurationFactory) with a method called NewConfiguration. Probably create two overloads, one that knows how o look up the appSetting itself, the other which just takes appSetting as a parameter (the value of appSetting being "A", "B" or "C", not the actual connect strings). Then NewConfiguration contains the ugly if/then/else or switch/case logic to decide which subclass to instantiate. The method returns whatever it creates as type ConfigurationBase.

This approach keeps all the branching crap out of your non-factory classes. Branching is kept to a minimum in the factory class, too -- just in one method. Each class has a specific responsibility, and doesn't try to be a jack-of-all-trades where each method and property is filled with senseless schizophrenia. Using the base class (or interface) type when referring to them outside of the factory frees you from caring which subtype even got instantiated. The code in each subclass will be much more straightforward.

[Jeffrey Tan[MSFT]]

Hi jdn,

Is your problem resolved?

For a quick start of .Net Reflection, please refer to:
http://msdn.microsoft.com/library/de...us/cpqstart/ht
ml/cpsmpnetsamples-howtoreflection.asp

It gives you a good and simple documentation and sample of Reflection.

If you have any further concern, please feel free to tell me, I will wor
with you.

Best regards,
Jeffrey Tan
Microsoft Online Partner Support
Get Secure! - www.microsoft.com/security
This posting is provided "as is" with no warranties and confers no rights.

[jdn]

I don't know yet for sure. I think that Philip's response that one should look at other alternatives is a valid one. Without further research and development, I can't say for certain.

But in the interim, I would say that the response I got was helpful in showing code that would do what I wanted, as well as suggesting other possibilities that might be better for the particular code situation I am looking at.

If I find anything that changes the 'interim response', I will post accordingly.

Thanks to all.

jdn

----- \"Jeffrey Tan[MSFT]\" wrote: -----
Hi jdn,

Is your problem resolved?

For a quick start of .Net Reflection, please refer to:
http://msdn.microsoft.com/library/de...us/cpqstart/ht
ml/cpsmpnetsamples-howtoreflection.asp

It gives you a good and simple documentation and sample of Reflection.

If you have any further concern, please feel free to tell me, I will wor
with you.

Best regards,
Jeffrey Tan
Microsoft Online Partner Support
Get Secure! - www.microsoft.com/security
This posting is provided "as is" with no warranties and confers no rights.

[Jeffrey Tan[MSFT]]

Hi jdn,

Thanks for your feedback.

No problem, please feel free to post, we will not ignore your post, :-)

I will help you at my best. (Do register your email address)

Best regards,
Jeffrey Tan
Microsoft Online Partner Support
Get Secure! - www.microsoft.com/security
This posting is provided "as is" with no warranties and confers no rights.