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05 April 2012

NHibernate: autocreate indexes for foreignkey

In these last days we have fallen in a performance issue with one of our DBs; the last and littlest one.

The creation of indexes on FKs seems to be a best-practice for MS-SQL-server and ORACLE and is not needed with Firebird; in Firebird instead than a best-practice is the default behavior: the FK includes an index.

That said I have to be sure that each FK has to have an index. After check our mappings I have realized that no one of our tables have the corresponding index for each FK.
Big PITA ?… no! that has been the lucky, because now I can create a very little piece of code to let NHibernate create all needed indexes for me.
public static class NHibernateConfigurationExtensions
{
    private static readonly PropertyInfo TableMappingsProperty =
        typeof(Configuration).GetProperty("TableMappings", BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);

    public static void CreateIndexesForForeignKeys(this Configuration configuration)
    {
        configuration.BuildMappings();
        var tables = (ICollection<Table>)TableMappingsProperty.GetValue(configuration, null);
        foreach (var table in tables)
        {
            foreach (var foreignKey in table.ForeignKeyIterator)
            {
                var idx = new Index();
                idx.AddColumns(foreignKey.ColumnIterator);
                idx.Name = "IDX" + foreignKey.Name.Substring(2);
                idx.Table = table;
                table.AddIndex(idx);
            }
        }
    }
}
and this is the code to have the migration-step script.
var configuration = CreateConfiguration();
configuration.CreateIndexesForForeignKeys();
var sb = new StringBuilder(500);
new SchemaUpdate(configuration).Execute(s => sb.Append(s), false);
Console.WriteLine(sb.ToString());
That is all… few minutes and everything done and checked for now on.

P.S. perhaps I'll be back to my blog...perhaps

14 comments:

  1. Welcome back to the land of the blog :)

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  2. Nice to know you're alive... and kicking... and haven't turned to Entity Framework! ;-)

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  3. Excelente que vuelvas a postear!!!

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  4. Yeah! I was missing your 'words of wisdom' on the NHibernate world. This is a very nice tip by the way, thanks for sharing.

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  5. Welcome back =) Nice post and thanks!

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  6. Welcome back!!!!

    ...and always great!

    :))

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  7. Nice trick but, know what? with entity framework and fluent nhibernate this is even easier :-P

    Glad to see you back!

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  8. @Juanma
    I don't think so. Let me see the code.

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  9. Fabio,

    I'd like to know how can I extend some LINQ class, so I can add a with(nolock) hint to every query performed using LINQ !

    Thanks !

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  10. @leonardo:
    You can write your own interceptor, inheriting from EmptyInterceptor, and overriding the OnPrepareStatement method. You set it on the Configuration object and build your ISessionFactory after it:

    using (ISessionFactory factory = cfg.SetInterceptor(new MyInterceptor()).BuildSessionFactory()) { ... }

    RP

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  11. Awesome tip, just saved me allot of dull, error prone work. Added it to our product and bang, it's allot faster.

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  12. Using NHibernate few years ago and could not find the source of this post, if not indicate much work as I can:
    http://nhforge.org/blogs/nhibernate/archive/2008/11/16/mapping-source-how-map-a-class-without-use-nothing.aspx

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  13. Heber
    This is WAY easier to use than NHibernate:
    https://www.kellermansoftware.com/p-47-net-data-access-layer.aspx

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