How to run odp.net application in both .net 3.5 and .net 4 - oracle

Question

I am working on an internal tool for our product. Our product uses oracle database and have evolved over time from .net framework 2.0 to 4.5 and Oracle 10 to 12.2.
The aim of the tool is to write a single application which works across different versions of the product.
I have solved the problem of multiple .net framework versions by using the following entries in app.config
<supportedRuntime version="v2.0.50727"/>
<supportedRuntime version="v4.0"/>
As the oracle managed .net driver is supported for framework >=4.0, I can not use this as I have to support .net framework 3.5 also.
As I have to use unmanaged odp.net driver, I was thinking about the following scenario
My tool would use the lowest version of oracle.dataaccess.dll and target .net 3.5.
Following #1 above makes me refer to 2.xx.... version of the oracle.dataaccess.dll.
When I run this application on a machine with only .net framework 4 installed, what would be the behavior? Would it load 4.xx... version of oracle.dataaccess dll when running under the context of .net framework 4?
The best solution for this would have been availability of oracle managed driver for .net 3.5 version but I found that it is not available.
Please provide your valuable inputs.
Satish
UPDATE :
I have written a sample application targeting .net framework 3.5. In this sample app, I will build a connection string and just open a connection and close it.
This application runs successfully when there are no <supportedRuntime> tags in the app.config.
When we add any <supportedRuntime> tags in the app.config, I am getting a type initializer exception for oracle related types. I have tried this with the supported run time tags
<supportedRuntime version="v2.0.50727"/>
<supportedRuntime version="v4.0"/>
individually and both combined. But I am still getting the issue. Can anyone suggest how to resolve this issue?

Answer 1

ODP.NET unmanaged driver exist in following versions:
1.x (.NET Framework 1.0.3705/1.1.4322), available up to Oracle Client 11.1.
2.0 (.NET Framework 2.0.50727), introduced with Oracle Client 10.2
4.0 (.NET Framework 4.0.30319), introduced with Oracle Client 11.2
If your compile target is .NET version 3 or 3.5 then the application will try to load ODP.NET version 2.0 (and will raise an exception if it is not found on the machine). Actually I am not sure if it would also accept ODP.NET version 4.0.
If your compile target is .NET version 4 or higher then the application will try to load ODP.NET version 4.0 (and will raise an exception if it is not found on the machine).
You can do several solutions:
Provide a copy of Oracle.DataAccess.dll which matches your version and put it in your application directory.
Use late binding, i.e. instead of
var con = new Oracle.DataAccess.Client.OracleConnection();
use
var DLL = Assembly.Load(String.Format("Oracle.DataAccess, Version={0}.{1}.*.*, Culture=neutral, PublicKeyToken=89b483f429c47342", frameworkVersion, oracleVersion));
var type = DLL.GetType("Oracle.DataAccess.Client.OracleConnection", true, false);
dynamic con = Activator.CreateInstance(type)
However, this syntax is only available from .NET Framework version 4.0 on, I do not know how to write this in version 3.0/3.5.
Note, use con.GetType().Assembly.FullName and con.GetType().Assembly.Location in order to see which DLL was really loaded.