On Tue, Oct 30, 2012 at 2:04 PM, Ted Elliott <elliott....@gmail.com> wrote:
> I like the solution but I'm not sure if it would work for us.  We are a
> multi-tenant app, and basically the string lookup is backed by another
> collection in the mongo database, with a couple of layers of cache
> in-between for performance.  The instance of the StringLookup would be
> different for each client database we're talking to, so it doesn't look
> like it would work to register it in the class map.  Is there a way around
> that?

> On Tuesday, October 30, 2012 12:03:05 PM UTC-4, Ted Elliott wrote:

>> Would it be possible to add some override points in the driver to do Linq
>> query transformation as well as some processing done on an object after its
>> deserialized but before its returned from the enumerator?  Here is what we
>> are trying to accomplish, we have some fields where we've "compressed" some
>> strings to save space in the database.  Basically we've taken a string,
>> stuck it in a lookup table to get back an int Id and the int gets stored in
>> the database.  We would like to put that as close to the database as
>> possible to make it more automatic and not require the developer to think
>> about it too much.  The object is modeled like this:

>> class Foo {
>>     [BsonIgnore]
>>     [MyCompressedField("BarId")]
>>     public string BarString { get; set; }

>>     [BsonElement("B")]
>>     public int BarId { get; set; }
>> }

>> So we want to do a few things here:
>> 1. Rewrite Linq queries so that when someone does FooCollection.Where(f
>> => f.BarString == "bar"), that is translated to FooCollection.Where(f =>
>> f.BarId == 123) which results in the mongo query: "{ B : 123 }". where 123
>> is the key for the string "bar".
>> 2. As the object comes out of the database repopulate our string field:
>>    f => { f.BarString = stringLookup.GetString(f.**BarId) }
>> 3. Inserts/Updates need to do the reverse:
>>    f=> { f.BarId = stringLookup.GetStringId(f.**BarString) }

>> We have 1 and 2 working, but we've had to wrap the MongoQueryProvider and
>> MongoQueryable in odd ways.  The BeginInit/EndInit methods don't really
>> work for this scenario as we require a reference to external object to do
>> the conversion, and it is not a singleton.

>> So could something like this be added so that we have some places to
>> register some callbacks to occur?  I would be willing to write the code if
>> I could get some pointers as to where the best places to put these would
>> be.  I think Item #1 seems like it would go on MongoCollection.

>> Thanks,
>> Ted