how does linq2sql keep track of database objects?

Question

Hi,

When using Linq2sql everything automagically works. My experience is that going with the flow is not always the best solution and to understand how something internally works is better so you use the technique optimally.

So, my question is about linq2sql.

If I do a query and get some database objects, or I create a new one, somehow the linqcontext object keeps references to these objects. If something changes in one of the objects, the context object 'knows' what has changed and needs updating.

If my references to the object are set to null, does this mean that the context object also removes it's link to this object? Or is the context object slowly getting filled with tons of references, and keeping my database objects from garbage collecting?

If not, how does this work??

Also, is it not very slow for the database object to always go through the entire list to see what changed and to update it?

Any insight in how this works would be excellent!

thanks

Answer 1

yes, the context keeps references of the loaded objects. That's one of the reasons why it isn't meant to be used with a single instance shared accross the different requests.

It keeps lists for the inserts/deletes. I am not sure if it captures update adding those to a list, or it loops at the end. But, u shouldn't be loading large sets of data at a time, because that alone would be a bigger hit to performance than any last check it might do on the list.

Answer 2

The DataContext registers to your objects PropertyChanged event to know when it is modified. At this point it clones the original object and keeps it to compare the 2 objects together later when you do your SubmitChanges().

If my references to the object are set to null, does this mean that the context object also removes it's link to this object?

Edit: No. Sorry for my original answer I had misinterpreted what you had written. In that case the data context still has a reference to both object but will remove the relationship with those 2 objects on next SubmitChanges().

Be careful though. If you created your own objects instead of using the ones generated from the .dbml, the "magic" that the datacontext performs might not work properly.