Question

I have very basic category model ID, RootCategoryID, Name and if I have category that has many childrens it won’t delete so I need to do this recursively but when I do so I get error.

I know that there is a work-around if I add MultipleActiveResultSets=true in connection string but AFAIK this can be solved from within code and it is not a good idea to use this parameter. Is this true?

Error

There is already an open DataReader associated with this Command which
must be closed first.

Code

public ActionResult Delete(int id)
{
    this.DeleteRecursive(id);
    _db.SaveChanges();
    return RedirectToAction("index", "category");
}

private void DeleteRecursive(int id)
{
    // Selecting current category
    var currentCategory = _db.Categories.Where(x => x.ID == id).Single(); // this line
    var childrenCategories = _db.Categories.Where(x => x.RootCategory.ID == id);

    // Check if category has children
    if (childrenCategories.Count() > 0)
    {
        // Loop through children and apply same function recrusively
        foreach (var c in childrenCategories)
        {
            this.DeleteRecursive(c.ID);
        }
    }

    // Category has no children left, delete it
    _db.Categories.Remove(currentCategory);
}

Answer 1

You’re leaving the DataReader open for the childrenCategories statement.

Apart from the exception, it means you’re executing the query twice – once to get the count and then again to get the data.

This should fix the problems:

var childrenCategories = _db.Categories
  .Where(x => x.RootCategory.ID == id)
  .ToList()
;

This executes the SQL statement and materializes all the records into a List.

So, you have your data in memory, and the DataReader is complete.