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Thursday, May 26, 2011

Simplifying use of SQL CE in Mango #WP7Dev (1 of n)

One of the features that the "Mango" tools introduce for Windows Phone development is a built in SQL Compact Edition (SQL CE) database. While learning about how to use it I was struck by how much better the experience could be.

As such, here is the first in what I hope will be a series of pointers and tips for making working with a database easier.

If you want to learn more about using SQL CE with Windows Phone codename "Mango" then I also recommend you check out the following on MSDN:
How to: Create a Basic Local Database Application for Windows Phone
and
Hands-On-Lab: Using local database in To-do application



When working with a database it's good practice to persist any changes to the datacache as quickly as possible. This means you'll probably end up doing something like this:
  db.MyItems.InsertOnSubmit(myNewItemInstance);
  db.SubmitChanges();
or this:
  db.MyItems.DeleteOnSubmit(anItemInstance);
  db.SubmitChanges();
quite a lot.

The only reason you may not want to do the above (Calling `SubmitChanges` after every call to `XxxxxOnSubmit()`) is if you were performing a number of insertions or deletions in a loop. In this case it may be wise (more performant) to call `SubmitChanges()` at the end.

When looking at even a short amount of code that does insertions or deletions it strikes me that there is a lot of duplication and that if those functions are always called together then it may make sense to bundle them up into a single function.

As it may not be immediately obvious how to do this (I had to explore a couple of options before I ended up with this), I present a simple class with some extension methods which does just that:

public static class TableExtensions
{
  public static void InsertAndSubmitChanges(this Table table, T entity) where T : class
  {
    table.InsertOnSubmit(entity);
    table.Context.SubmitChanges();
  }

  public static void DeleteAndSubmitChanges(this Table table, T entity) where T : class
  {
    table.DeleteOnSubmit(entity);
    table.Context.SubmitChanges();
  }
}  

By using the above class, it means that where we were previously having to write 2 lines of code we can now just write 1 and still get the same functionality!

  db.MyItems.InsertAndSubmitChanges(myNewItemInstance);

  db.MyItems.DeleteAndSubmitChanges(anItemInstance);  

I hope this helps you write less code. (In a good way of course.)
Please let me know if you find this helpful.

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