I'm trying to implement data localization logic for Entity Framework. So that if for example a query selects Title property, behind the scenes it should reference the column Title_enGB or Title_deCH depending on the current user culture .

To achieve this, I'd like to rewrite the DbExpression CommandTrees from Entity Framework. I thought these trees are a new common .NET way for building cross database insert/update/select queries.. But now all relevant constructors/factories in the namespaces System.Data.Metadata and System.Data.Common.CommandTrees in System.Data.Entity.dll are internal!! (In msdn documentated as public, like: DbExpressionBuilder).

Does anyone have an idea to achieve this query manipulation with or without query tree rewrite?

my desired code: (public class DbProviderServicesWrapper : DbProviderServices)

/// <summary>
/// Creates a command definition object for the specified provider manifest and command tree.
/// </summary>
/// <param name="providerManifest">Provider manifest previously retrieved from the store provider.</param>
/// <param name="commandTree">Command tree for the statement.</param>
/// <returns>
/// An exectable command definition object.
/// </returns>
protected override DbCommandDefinition CreateDbCommandDefinition(DbProviderManifest providerManifest, DbCommandTree commandTree)
{
    var originalCommandTree = commandTree as DbQueryCommandTree;
    if (originalCommandTree != null)
    {
        var expression = new MyCustomQueryRewriter(originalTree.MetadataWorkspace).Visit(originalCommandTree.Query);
        commandTree = DbQueryCommandTree.FromValidExpression(originalCommandTree.MetadataWorkspace, originalCommandTree.DataSpace, expression);
    }

    // TODO: UpdateCommand/InsertCommand

    var inner = this.Inner.CreateCommandDefinition(providerManifest, commandTree);
    var def = new DbCommandDefinitionWrapper(inner, (c, cd) => new DbCommandWrapper(c));

    return def;
}

Update

Having two title columns on one table isn't cool but its easier to implement in a first step. Later I'll join an other table with the localized fields, so the main table will only contain invariant data.