如何使用ODAC C＃连接到Oracle数据库

Question

I am using this code but getting an error of 'Object reference not set to an instance of an object.' at con.open() ? what am I doing wrong ?

I have already download and installed ODAC component version 10 , 11 ,12 trying each one at the failure of the latest one but still same error

using Oracle.DataAccess.Client;


namespace WindowsFormsApplication1
{
    class OraTest
    {

        public OracleConnection con = new OracleConnection();
        public void Connect()
        {
            con.ConnectionString = "Data Source=(DESCRIPTION= (ADDRESS = (PROTOCOL = TCP)(HOST =myip) (PORT = myport))(CONNECT_DATA = (SERVER = dedicated)(SERVICE_NAME = mydb)));User ID=myid;Password=mypass;";

            con.Open(); //error here

        }

        public void Close()
        {
            con.Close();
            con.Dispose();
        }


    }

Answer 1

If you add a try/catch block in Connect(), you'll be able to catch the error.

For example:

When opening an oracle connection, connection object is null

I added the try catch block, and it returned ORA12154 - TNS could not be resolved. After some research, I added an SID to my tnsnames.ora file in my ODP for .NET Oracle home path, and it worked

See also Troubleshooting Oracle Net Services for troubleshooting possible connection issues from Oracle clients (such as your C# program).

But your first step is absolutely to determine the Oracle-level error (for example, ORA-12543 (could not connect to server host) or TNS-12514 (could not find service name)

MSDN: OracleException Class

public void ShowOracleException() 
{
   OracleConnection myConnection =
      new OracleConnection("Data Source=Oracle8i;Integrated Security=yes");

   try 
   {
      myConnection.Open();
   }
   catch (OracleException e) 
   {
     string errorMessage = "Code: " + e.Code + "\n" +
                           "Message: " + e.Message;

     System.Diagnostics.EventLog log = new System.Diagnostics.EventLog();
     log.Source = "My Application";
     log.WriteEntry(errorMessage);
     Console.WriteLine("An exception occurred. Please contact your system administrator.");
   }
}

It's significant that con.ConnectionString = xyz works, but the following `con.Open()" fails. This means .Net is creating the C# object, but Oracle/TNS is failing when you try to use it.

ADDITIONAL SUGGESTIONS:

• Re-read

  When opening an oracle connection, connection object is null .

  Read all of the suggestions, including the one about "Data Source in your connection string".

• Focus on your connection string. It couldn't hurt to specify the connection string in your OracleConnection() constructor, if possible. Here's another link:

  ODP.NET Connection exception

• It would be great if you can verify connectivity from your PC with some other Oracle client, besides your C#/.Net program. To verify you're talking to the right TNS host and service, with the correct username/password. For example, maybe you have SQLDeveloper or sqlplus.

• Finally, re-read the TNS troubleshooting link:

  https://docs.oracle.com/cd/E11882_01/network.112/e41945/trouble.htm#NETAG016

Answer 2

Please go through this link

Getting Started with Oracle Data Provider for .NET (C# Version)

http://www.oracle.com/webfolder/technetwork/tutorials/obe/db/dotnet/GettingStartedNETVersion/GettingStartedNETVersion.htm

Answer 3

What worked for me with the same error was to simply switch from the 'plain' Oracle DataAccess library, to the 'Managed' version. This is an extemely easy change to make -

1. Add a Reference in your c# project to the Oracle.ManagedDataAccess library

2. Replace the existing use statements at the top of your Oracle client code with the following:

    using Oracle.ManagedDataAccess.Client; using Oracle.ManagedDataAccess.Types; 

3. Include the Oracle.ManagedDataAccess.dll file with your exe