If you decide to connect to Oracle DB using Visual Studio you should follow the mentioned instruction below:
Make sure that the Instance Oracle Client and Oracle Data Provider for .Net (x64) have been installed. (To download and install Instance Oracle Client and Oracle Data Provider check this )
Open Visual Studio > Tools Menu > Select Connect to Database.
OCIEnvCreate failed with return code -1 during using Oracle Client in SharePoint Visual WebPart
OCIEnvCreate failed with return code -1 during using Oracle Client in SharePoint Visual WebPart
Although I have been installed oracle client in my server I got the following error
OCIEnvCreate failed with return code -1
When I tried to use oracle client to access oracle database in SharePoint Visual WebPart.
I investigated this issue by creating a new windows application and also ASP.Net web application then using the same current installed oracle client dll that has been worked properly.