This code compacts and repairs an MS Access database from a C# .NET application

Introduction
This code compacts and repairs an MS Access database from a C# .NET application, no matter if it's a simple ".mdb", or a ".mdw"-secured workgroup-shared DB. It performs exactly the same operation as "Tools - Database Utils - Compact and Repair Database..." menu item in the MS Access application. The code uses "late binding" (creating COM-objects in memory at runtime), and that's why you don't need any annoying interop COM references in your project. You don't even need MS Office installed. Just make sure you have a Jet Engine (Jet is included in MDAC package, which comes with any Windows installation starting from NT 4).

Background
Don't you hate COM-library references in .NET-projects? I believe that pure .NET-code has to be free of any interops, RCWs, and other referenced COM-stuff. Basically because there's a load of different versions of MS libraries (for example, MS Office Object Library 9, 10, 11 etc.). We never know what version of MS Office is installed on a client machine, that's why we should access a COM-object via ProgID, and not CLSID. For example: you want to be sure, that when you call for an "Excel.Application", you get Excel, no matter what version of MS Office is installed. And when you add a reference "MS Excel 10 Object library", you add a strong limitation to your software! So... use System.Reflection and late binding.

Using the code
Just call a method CompactAccessDB. This method compacts and repairs your database.

Parameters:

connectionString - connection string to your database.
mdwfilename - is a full name (path+name) of an MDB-file you want to compact and repair.
Due to Jet limitations, the method compacts your database to a new file, so we have to copy the new compacted file over an old one.

When you call this method, make sure that there's no open connections to your database. Stop your threads.

Now, to the code:

/**//// <summary>
/// MBD compact method (c) 2004 Alexander Youmashev
/// !!IMPORTANT!!
/// !make sure there's no open connections
///    to your db before calling this method!
/// !!IMPORTANT!!
/// </summary>
/// <param name="connectionString">connection string to your db</param>
/// <param name="mdwfilename">FULL name
///     of an MDB file you want to compress.</param>
public static void CompactAccessDB(string connectionString, string mdwfilename)
{
    object[] oParams;

    //create an inctance of a Jet Replication Object
    object objJRO = 
      Activator.CreateInstance(Type.GetTypeFromProgID("JRO.JetEngine"));

    //filling Parameters array
    //cnahge "Jet OLEDB:Engine Type=5" to an appropriate value
    // or leave it as is if you db is JET4X format (access 2000,2002)
    //(yes, jetengine5 is for JET4X, no misprint here)
    oParams = new object[] {
        connectionString,
        "Provider=Microsoft.Jet.OLEDB.4.0;Data" + 
        " Source=C:\\tempdb.mdb;Jet OLEDB:Engine Type=5"};

    //invoke a CompactDatabase method of a JRO object
    //pass Parameters array
    objJRO.GetType().InvokeMember("CompactDatabase",
        System.Reflection.BindingFlags.InvokeMethod,
        null,
        objJRO,
        oParams);

    //database is compacted now
    //to a new file C:\\tempdb.mdw
    //let's copy it over an old one and delete it

    System.IO.File.Delete(mdwfilename);
    System.IO.File.Move("C:\\tempdb.mdb", mdwfilename);

    //clean up (just in case)
    System.Runtime.InteropServices.Marshal.ReleaseComObject(objJRO);
    objJRO=null;
}

Points of Interest
Interesting, that Jet Engine 5 is used for JET4X databases. Be careful. See the table:

Jet OLEDB:Engine Type Jet x.x Format MDB Files
1 JET10
2 JET11
3 JET2X
4 JET3X
5 JET4X