change connection string in class application at runtime?

I have class application that uses ado.net to c开发者_StackOverflow中文版onnect to Sqlite database. The application uses the db to store some data and the db may be changed at run time. The user may make backups of the db and change the location, but in this case i need to know how to change the connection string. I have tried this code but it didn't work:

string conn =
    @"metadata=res://*/KzDm.csdl|res://*/KzDm.ssdl|res://*/KzDm.msl;" +
    @"provider=System.Data.SQLite;" +
    @"provider connection string=" +
    @""" +@"Data Source=" +
    @"F:\My Own programs\KrarZara2\KZ\KZ\Kzdb.s3db" +
    @""";

Entities ent = new
Entities(conn);

this error "Keyword not supported: 'data source'." happen at this line

 public Entities(string connectionString) : base(connectionString, "Entities")

i write that and it worked with me

EntityConnectionStringBuilder conn = new EntityConnectionStringBuilder();
        conn.Metadata = @"res://*/KzDm.csdl|res://*/KzDm.ssdl|res://*/KzDm.msl";
        conn.Provider = "System.Data.SQLite";
        conn.ProviderConnectionString = @"data source=F:\My Own programs\KrarZara2\KZ\KZ\KrarDS.krar;Version=3;";
        EntityConnection entity = new EntityConnection(conn.ConnectionString);
        using (DmEnt ent = new DmEnt(entity))
        {
            var parcel = ent.Parcels.SingleOrDefault(d => d.id == 1);
            var pparcc = ent.Parcels.Select(d => d.id == 2);
            Parcel r = new Parcel();
            r.ParcelNumber = "11ju";
            r.Area = 8787;

            ent.AddToParcels(r);
            ent.SaveChanges();
        }

Dm ent is the entity model in edmx ado.net

wrong line order, should be:

    @""" +
    @"Data Source=" +

I'd actually surprised that connection string works at all. In addition, it would be simpler to use string.Format to build this connection string:

var filename = @"F:\My Own programs\KrarZara2\KZ\KZ\Kzdb.s3db";
var connString = string.Format("Data Source={0};UseUTF16Encoding=True;", filename );

using( var conn = new SQLiteConnection( connString ) )
{
    ...
}

First, you would replace UseUTF16Encoding with the proper value for your setup. Second, note that the file path in the connection string is not surrounded by quotation marks.

If you are looking for a means to swap Sqlite data files at runtime you might look at this blog entry:

SQLite and Entity Framework 4

A summary of the solution is to parse the Entity framework connection string, change the data file and then reset it:

public static string RedirectedEntityFrameworkConnectionString(string originalConnectionString, string databaseFile, string password)
{
    // Parse the Entity Framework connection string.
    var connectionStringBuilder = new EntityConnectionStringBuilder(originalConnectionString);
    if (connectionStringBuilder.Provider != "System.Data.SQLite")
    {
        throw new ArgumentException("Entity Framework connection string does not use System.Data.SQLite provider.");
    }

    // Parse the underlying provider (SQLite) connection string.
    var providerConnectionStringBuilder = new SQLiteConnectionStringBuilder(connectionStringBuilder.ProviderConnectionString);

    // Redirect to the specified database file, and apply encryption.
    providerConnectionStringBuilder.DataSource = databaseFile;
    providerConnectionStringBuilder.Password = password;

    // Rebuild the Entity Framework connection string.
    connectionStringBuilder.ProviderConnectionString = providerConnectionStringBuilder.ConnectionString;
    return connectionStringBuilder.ConnectionString;
}

To use, you would do something like:

const string OriginalConnectionString = "..."; // (Copy out of app.config)
var connectionString = RedirectedEntityFrameworkConnectionString(OriginalConnectionString, myFileName, null);
using (var context = new MyEntities(connectionString))
{
    ...
}