Question

We currently have a production application that runs as a windows service. Many times this application will end up in a loop that can take several hours to complete. We are using Entity Framework for .net 4.0 for our data access.

I’m looking for confirmation that if we load new data into the system, after this loop is initialized, it will not result in items being added to the loop itself. When the loop is initialized we are looking for data “as of” that moment. Although I’m relatively certain that this will work exactly like using ADO and doing a loop on the data (the loop only cycles through data that was present at the time of initialization), I am looking for confirmation for co-workers.

Thanks in advance for your help.

//update : here’s some sample code in c# – question is the same, will the enumeration change if new items are added to the table that EF is querying?

IEnumerable<myobject> myobjects = (from o in db.theobjects where o.id==myID select o);
foreach (myobject obj in myobjects)
{
    //perform action on obj here
}

Answer 1

It depends on your precise implementation.

Once a query has been executed against the database then the results of the query will not change (assuming you aren’t using lazy loading). To ensure this you can dispose of the context after retrieving query results–this effectively “cuts the cord” between the retrieved data and that database.

Lazy loading can result in a mix of “initial” and “new” data; however once the data has been retrieved it will become a fixed snapshot and not susceptible to updates.

You mention this is a long running process; which implies that there may be a very large amount of data involved. If you aren’t able to fully retrieve all data to be processed (due to memory limitations, or other bottlenecks) then you likely can’t ensure that you are working against the original data. The results are not fixed until a query is executed, and any updates prior to query execution will appear in results.