Saturday, February 28, 2009

Querying SDS - Sorting

This is the fifth part of a series of posts about SQL Data Services (SDS). Last time I showed the basics of how to query SDS, now I will show some more query options. Let’s start with the basic query from last time that returns all the entities in a container

from e in entities select e

By default the entities will be sorted by the Id property. We can sort by other properties like this

from e in entities orderby e["DateDue"] select e

Note that just like in the Where clause flexible properties in the orderby clause use the syntax like e[“DateDue”] but metadata properties use the e.Verison syntax. By default the sort is done in ascending order. You can sort descending like this:

from e in entities orderby e["DateDue"] descending select e

You can also sort by multiple properties

from e in entities orderby e["Completed"],e["DateDue"] select e

As I have mentioned before SDS entities are schema-less so there could be entities in a container that don’t have one of the properties you are sorting on. In these cases the entities will still appear in the output. I have not seen any official documentation that explains how these are handled but it appear they are treated as having a null value and are sorted to the top of the list.

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