I'd like to know if is there something like a Trigger (of databases) in NHibernate that I can use per entity ?
I'd like to make a history of each record, and with triggers I can compare the old value and new value of each property and generate a register of history.
I've heard about Audit in NHibernate, but it's for all entities, if there isn't another way... how Can I separete a block per entity ?
Thanks
Related
Lets say I have entity A, which have many to many relationship with another entities of type A. So on entity A, I have collection of A. And lets say I have to "update" this relationships according to some external service - from time to time I receive notification that relations for certain entity has changed, and array of IDs of current related entities - some relations can be new, some existing, some of existing no longer there... How can I effectively update my database with EF ?
Some ideas:
eager load entity with its related entities, do foreach on collection of IDs from external service, and remove/add as needed. But this is not very effective - need to load possibly hundreds of related entities
clear current relations and insert new. But how ? Maybe perform delete by stored procedure, and then insert by "fake" objects
a.Related.Add(new A { Id = idFromArray })
but can this be done in transaction ? (call to stored procedure and then inserts done by SaveChanges)
or is there any 3rd way ?
Thanx.
Well, "from time to time" does not sound like a situation to think much about performance improvement (unless you mean "from millisecond to millisecond") :)
Anyway, the first approach is the correct idea to do this update without a stored procedure. And yes, you must load all old related entities because updating a many-to-many relationship goes only though EFs change detection. There is no exposed foreign key you could leverage to update the relations without having loaded the navigation properties.
An example how this might look in detail is here (fresh question from yesterday):
Selecting & Updating Many-To-Many in Entity Framework 4
(Only the last code snippet before the "Edit" section is relevant to your question and the Edit section itself.)
For your second solution you can wrap the whole operation into a manually created transaction:
using (var scope = new TransactionScope())
{
using (var context = new MyContext())
{
// ... Call Stored Procedure to delete relationships in link table
// ... Insert fake objects for new relationships
context.SaveChanges();
}
scope.Complete();
}
Ok, solution found. Of course, pure EF solution is the first one proposed in original question.
But, if performance matters, there IS a third way, the best one, although it is SQL server specific (afaik) - one procedure with table-valued parameter. All new related IDs goes in, and the stored procedure performs delete and inserts in transaction.
Look for the examples and performance comparison here (great article, i based my solution on it):
http://www.sommarskog.se/arrays-in-sql-2008.html
I'm trying to use 'adonet.batch_size' property in NHibernate. Now, I'm creating entities across multiple sessions at a large rate (hence batch inserting). So what I'm doing is creating a buffer where I keep these entities and them flush them out all at once periodically.
However I need the ID's as soon as I create the entities. So I want to create an entity (in any session) and then have its ID generated (I'm using HiLo generator). And then at a later time (and other session) I want to flush that buffer and ensure that those IDs do not change.
Is there anyway to do this?
Thanks
Guido
I find it odd that you need many sessions to do a single job. Normally a single session is enough to do all work.
That said, the Hilo generator sets the id property on the entity when calling nhSession.Save(object) without necessarily requiring a round-trip to the database and a
nhSession.Flush() will flush the inserts to the database
UPDATE ===========================================================================
This is a method i used on a specific case that made pure-sql inserts while maintaining NHibernate compatibility.
//this will get the value and update the hi-lo value repository in the datastore
public static void GenerateIdentifier(object target)
{
var targetType = target.GetType();
var classMapping = NHibernateSessionManager.Instance.Configuration.GetClassMapping(targetType);
var impl = NHibernateSessionManager.Instance.GetSession().GetSessionImplementation();
var newId = classMapping.Identifier.CreateIdentifierGenerator(impl.Factory.Dialect, classMapping.Table.Catalog, classMapping.Table.Schema,
classMapping.RootClazz).Generate(impl, target);
classMapping.IdentifierProperty.GetSetter(targetType).Set(target, newId);
}
So, this method takes your newly constructed entity like
var myEnt = new MyEnt(); //has default identifier
GenerateIdentifier(myEnt); //now has identifier injected based on nhibernate's mapping
note that this call does not place the entity in any kind of nhibernate managed space. So you still have to make a place to place your objects and make the save on each one. Also note that i used this one with pure sql inserts and unless you specify generator="assigned" (which will then require some custom hi-lo generator) in your entity mapping nhibernate may require a different mechanism to persist it.
All in all, what you want is to generate an Id for an object that will be persisted at some time in the future. This brings up some problems such as handling non-existent entries due to rollbacks and failed commits. Additionally imo nhibernate is not the tool for this particular job, you don't need nhibernate to do your bulk insert unless there is some complex entity logic that is too costly (in dev time) to implement on your own.
Also note that you are implying that you need transient detached entities which however cannot be used unless you call .nhSes.Save(obj) on the first session and flush its contents so the 2nd session when it calls Load on the transient object there will be an existing row in the database which contradicts what you want to achieve.
Imo don't be afraid of storming the database, just optimise the procedure top-to-bottom to be able to handle the volume. Using nhibernate just to do an insert seems counter-productive when you can achieve the same result with 4 times the performance using ado.net or even an isqlquery wrapped-query (and use the method i provided above)
I've already read NHibernate - Changing sub-types and I don't find that satisfactory to my situation.
My system allows users to schedule jobs. Schedules can be set up with different types of schedule criteria (Once only, Daily, Weekly, Monthly by day of month, and Monthly by week of month). Each of these have very different data and behavior. It is perfectly valid for a user to change a schedule from one criteria type to another.
I attempted to make this work by grabbing the schedule id that was saved previously, creating a new instance of the schedule with the new type, setting the id, and saving. All of the data was updated as expected, except, of course, the discriminator.
Changing my model would be an absolute last resort.
At this point, I am looking at saving the new criteria (with a new id) and updating the references to it, then deleting the old criteria.
Does someone have a better idea?
Have you tried modifing your disciminator mapping to add force=true like the following hbm.xml element
<discriminator column="DiscriminatorColumnName" force="true" />
Since you're already bending the NHibernate view of object identity, why don't you just update it outside of NHib using some custom SQL?
My preferred solution would be to update my model, but you've said that that's a last resort for you.
If you want to use NHibernate, then the concession you must make is:
Write object-oriented code.
If your particular case is arduous to express in an object-oriented manner, then you should not be using NHibernate for that case.
For your case, you should:
create a new instance of a class deriving Schedule, and permit it to have a new ID
copy the relevant properties from the old Schedule instance
delete the old Schedule instance from the Session and ensure that the Job instance in question does not reference it
add the new Schedule instance to the Session and ensure that the Job instance in question references it
This will end up, at the database level, as a delete and insert, rather than an update.
This is not a last resort. This should have been your first resort. This is the right way to do it from an object-oriented perspective.
I am wondering how can one delete an entity having just its ID and type (as in mapping) using NHibernate 2.1?
If you are using lazy loading, Load only creates a proxy.
session.Delete(session.Load(type, id));
With NH 2.1 you can use HQL. Not sure how it actually looks like, but something like this: note that this is subject to SQL injection - if possible use parametrized queries instead with SetParameter()
session.Delete(string.Format("from {0} where id = {1}", type, id));
Edit:
For Load, you don't need to know the name of the Id column.
If you need to know it, you can get it by the NH metadata:
sessionFactory.GetClassMetadata(type).IdentifierPropertyName
Another edit.
session.Delete() is instantiating the entity
When using session.Delete(), NH loads the entity anyway. At the beginning I didn't like it. Then I realized the advantages. If the entity is part of a complex structure using inheritance, collections or "any"-references, it is actually more efficient.
For instance, if class A and B both inherit from Base, it doesn't try to delete data in table B when the actual entity is of type A. This wouldn't be possible without loading the actual object. This is particularly important when there are many inherited types which also consist of many additional tables each.
The same situation is given when you have a collection of Bases, which happen to be all instances of A. When loading the collection in memory, NH knows that it doesn't need to remove any B-stuff.
If the entity A has a collection of Bs, which contains Cs (and so on), it doesn't try to delete any Cs when the collection of Bs is empty. This is only possible when reading the collection. This is particularly important when C is complex of its own, aggregating even more tables and so on.
The more complex and dynamic the structure is, the more efficient is it to load actual data instead of "blindly" deleting it.
HQL Deletes have pitfalls
HQL deletes to not load data to memory. But HQL-deletes aren't that smart. They basically translate the entity name to the corresponding table name and remove that from the database. Additionally, it deletes some aggregated collection data.
In simple structures, this may work well and efficient. In complex structures, not everything is deleted, leading to constraint violations or "database memory leaks".
Conclusion
I also tried to optimize deletion with NH. I gave up in most of the cases, because NH is still smarter, it "just works" and is usually fast enough. One of the most complex deletion algorithms I wrote is analyzing NH mapping definitions and building delete statements from that. And - no surprise - it is not possible without reading data from the database before deleting. (I just reduced it to only load primary keys.)
I've got a parent and child object. Depending on a value in the parent object changes the table for the child object. So for example if the parent object had a reference "01" then it will look in the following table "Child01" whereas if the reference was "02" then it would look in the table "Child02". All the child tables are the same as in number of columns/names/etc.
My question is that how can I tell Fluent Nhibernate or nhibernate which table to look at as each parent object is unique and can reference a number of different child tables?
I've looked at the IClassConvention in Fluent but this seems to only be called when the session is created rather than each time an object is created.
I found only two methods to do this.
Close and recreate the nhibernate session every time another dynamic table needs to be looked at. On creating the session use IClassConvention to dynamically calculate the name based on user data. I found this very intensive as its a large database and a costly operation to create the session every time.
Use POCO object for these tables with custom data access.
As statichippo stated I could use a basechild object and have multiple child object. Due to the database size and the number of dynamic table this wasn't really a valid option.
Neither of my two solutions I was particularly happy with but the POCO's seemed the best way for my problem.
NHibernate is intended to be an object relational mappers. It sounds like you're doing more of a scripting style and hoping to map your data instead of working in an OOP manner.
It sounds like you have the makings of an class hierarchy though. What it sounds like you're trying to create in your code (and then map accordingly) is a hierarchy of different kinds of children:
BaseChild
--> SmartChild
--> DumbChild
Each child is either smart or dumb, but since they all have a FirstName, LastName, Age, etc, they all are instances of the BaseChild class which defines these. The only differences might be that the SmartChild has an IQ and the DumbChild has a FavoriteFootballTeam (this is just an example, no offense to anyone of course ;).
NHibernate will let you map this sort of relationship in many ways. There could be 1 table that encompasses all classes or (what it sounds like you want in your case), one table per class.
Did I understand the issue/what you're looking for?