Found a great article on how to implement optimistic concurrency with LLBLGEN and SQL Server:
Optmistic Concurrency and Timestamps in SQL Server Using LLBLGen Pro O/R Mapper by David Hayden.
Now, I am using XML Web Services and passing entities back and forth, and what I have found is that the DBValue property on each field is NOT serialized! I have not found a better solution as yet, but I am currently just using the field's CurrentValue. So, assuming the timestamp properties used do not get changed on the client, it will work, but this is a problem that will need to be fixed.
Update: Looks like there was an issue with the deserialization in version 2.5 (October 25 2007 release). The December release has apparently fixed this issue:
http://www.llblgen.com/TinyForum/Messages.aspx?...
Modifications with LLBLGEN 2.5
I am inherently lazy, which is a bad thing when it comes to coding, but the solution described by LLBLGEN's help and David Hayden relies on a factory class for each entity. Sure, we should probably modify the templates and create a new factory class for each of our entities, but for what I wanted, that sounded like too much work.
Now, in LLBLGEN 2.5, all entities are now derived from another generated partial class called CommonEntityBase. And, lets face it, we are probably going to create our timestamp field on every entity and call it the same name (in this case, every entity has a timetamp field called LastModified). So, I created a new partial class definition for CommonEntityBase that allows me to get access to the timestamp field I will use for all entities' concurrency control.
public partial class CommonEntityBase
{
private const string LAST_MODIFIED_FIELD_NAME = "LastModified";
public IEntityField2 LastModifiedField
{
get { return this.Fields[LAST_MODIFIED_FIELD_NAME]; }
}
}
This then allows me to create a single factory for concurrency predicate expressions:
public class EntityConcurrencyFactory : IConcurrencyPredicateFactory
{
public IPredicateExpression CreatePredicate(ConcurrencyPredicateType predicateTypeToCreate,
object containingEntity)
{
IPredicateExpression toReturn = new PredicateExpression();
CommonEntityBase entity = (CommonEntityBase)containingEntity;
switch (predicateTypeToCreate)
{
case ConcurrencyPredicateType.Delete:
case ConcurrencyPredicateType.Save:
// only for updates
toReturn.Add(new FieldCompareValuePredicate(entity.LastModifiedField,
null, ComparisonOperator.Equal, entity.LastModifiedField.CurrentValue));
break;
}
return toReturn;
}
}
Two classes for all entities - sounds good to me. Now, using David's example, there isn't any difference in the code (just every entity uses the same factory):
DataAccessAdapter adapter = new DataAccessAdapter(...);
BlogEntity blog = new BlogEntity();
blog.BlogId = 1;
adapter.FetchEntity(blog);
blog.Name = "New Name";
IPredicateExpression expression = new EntityConcurrencyFactory()
.CreatePredicate(ConcurrencyPredicateType.Save, blog);
adapter.SaveEntity(blog, true, expression);
You can still change optimistic concurrency strategies easily, but it is easier to apply to all of your entities at once.
