LINQ - XElement and Entities
With LINQ we get a common data programming experience across multiple data sources. We can query in-memory collections, relational tables and XML. The other day I was looking at the various LINQ-XML examples and thought to myself that I would like to play around with loading my database from a remote XML source. Using XElement this becomes quite easy… I can load XML from a remote source, filter out the data that I care about and use this data to instantiate and persist data in my local database. Being a basketball fan I figured I would try this out with sports information, following is a discussion of my little experiment in this regard:
Loading Data From A Remote Data Source:
The first thing I needed was some sports information from a remote source, I went on live.com and did a search for sports information. I came across an XML format for sports information called SportsML and an URL with sample basketball data. For this exercise I figured that this would be a reasonable source for my endeavor.
Retrieving the information in a form that I can use LINQ over it is trivial, given a URL:
private String _sportsML = @"http://www.sportsml.org/IPTC/SportsML/1.7/examples/sportsml-basketball_standings.xml";
I can use the Load method on the XElement class as my starting point:
XElement sports = XElement.Load(_sportsML);
I can now perform LINQ queries over this to retrieve the data I want. The sportsML schema provides results, schedules and more, I just wanted to pull out schedules which I did as follows:
protected IEnumerable<XElement> GetSchedule()
{
XElement sports = XElement.Load(_sportsML);
var schedule = from s in sports.Elements()
where s.Name.LocalName == "schedule"
select s;
return schedule;
}
Given a schedule I can further use LINQ to pull out the pieces of the schedule that I want. For this exercise I will use LINQ to pull the date & time plus the participating teams:
Retrieve the Date:
protected String GetEventDateTime(XElement sportsEvent)
{
var dateTimeResult = from eventMetadata in sportsEvent.Elements()
where eventMetadata.Name.LocalName == "event-metadata"
from evDateTime in eventMetadata.Attributes() where evDateTime.Name.LocalName == "start-date-time"
select evDateTime;
return (dateTimeResult.Count() > 0) ? dateTimeResult.First().Value : null;
}
Retrieve the Teams:
protected String[] GetTeams(XElement sportsEvent)
{
var teamNames = from teams in sportsEvent.Elements()
where teams.Name.LocalName == "team"
from teamMetadata in teams.Elements()
where teamMetadata.Name.LocalName == "team-metadata"
from nameElement in teamMetadata.Elements()
select nameElement.Attribute("first").Value +" "+ nameElement.Attribute("last").Value;
return teamNames.ToArray<String>();
}
With this information at hand I can now create persistent instances that I will save using the ADO.NET Entity Framework:
protected SportsEvent CreateSportsEvent(XElement sportsEvent)
{
SportsEvent entitySportsEvent = null;
String dateTimeAsString = GetEventDateTime(sportsEvent);
if (null != dateTimeAsString)
{
String[] teamNames = GetTeams(sportsEvent);
entitySportsEvent = new SportsEvent();
entitySportsEvent.EventDateTime = DateTime.Parse(dateTimeAsString);
entitySportsEvent.AwayTeam = teamNames[0];
entitySportsEvent.HomeTeam = teamNames[1];
}
return entitySportsEvent;
}
Saving this is merely a matter of adding the instance to the ObjectContext and saving:
public void ScheduleReader()
{
BlogRssContext context = new BlogRssContext();
IEnumerable<XElement> schedule = GetSchedule();
foreach (XElement sportsEvent in schedule.Elements())
{
SportsEvent entitySportsEvent = CreateSportsEvent(sportsEvent);
if (null != entitySportsEvent)
{
context.AddObject(entitySportsEvent);
}
}
context.SaveChanges();
}
With that we have pulled data from a remote service and persisted it in a local database.
Tim Mallalieu
Program Manager, ADO.NET
