LINQ to SQL How can I submit changes after closing the connection?

Question

I am accessing a database using LINQ, and making changes to the records. I retrieve the records like so:

using(var db = new DatabaseDataContext(connectionString))
{
    var query =
        from item in db.table
        where item.senddate == null
        select item;

    results = query.ToList();
}

After getting the items, I process each one, which requires communication with a web service, and can take more than a minute per record. When the record has been updated, I need to submit the changes, but I am not sure how to proceed. Currently, I do the following:

List<table> toProcess = QueryDb();  // Calls the previously displayed method

foreach (table item in toProcess)
{
     item.result = QueryDb(item.xmlrequest);
     PostToDb(item);
}

...

private bool PostToDb(table submit)
{
    submit.senddate = DateTime.Now;

    using (var db = new DatabaseDbDataContext(connectionString))
    {
        db.SubmitChanges();
    }

    return result;
}

db.SubmitChanges() does not submit any changes, but I haven't really set that the object "submit" holds the changes. How do I submit the changes made to the entry without keeping the Db connection open for several minutes while the files are processed one at a time?

Thank you in advance for any assistance.

PARTIALLY RESOLVED

I don't think this is the best solution, but I was able to get it to work with the following changes to my code:

private bool PostToDb(table submit)
{
    using (var db = new DatabaseDataContext(connectionString))
    {
        var query =
            from item in db.table
            where item.iprimaryid.Equals(submit.iprimaryid)
            select item;

        //  There can only be one result, but this was the only 
        //  way I could think to access it
        foreach (var item in query)
        {
            item.senddate = DateTime.Now;
            item.result = submit.result;
        }

        db.SubmitChanges();
    }

    return result;
}

Answer 1

You need to use the Attach method for your DataContext. So, your steps are:

1) Query object from the database using one instance of your DataContext
2) Make some changes
3) Create the new DataContext instance and attach modified entities.

using (var dataContext = new DataContext(ConnectionString))
{
     dataContext.TABLE_NAME.Attach(modifiedEntity);
     dataContext.SubmitChanges();
}

Answer 2

Can you declare your data context in an outer scope and pass it as a parameter to the methods that need to access the database? Something like this:

using (var db = new DatabaseDbDataContext(connectionString))
{
    var toProcess = QueryDb(db);

    // Do whatever processing you need to do...

    toProcess.ForEach(t => t.SendDate = DateTime.Now);

    db.SubmitChanges();
}