I have two separate queries that both return the same IQueryable, and I'd like to combine them prior to projection. It looks like neither Union or Concat are implemented in Linq to NHibernate? Does anyone know how I might go about achieving this?
It's not possible. You'll have to do it on the client.
Example:
var allItems = queryable1.AsEnumerable().Concat(queryable2)
#Diago Mijelshon gives a good answer, but I would like to add that depending on what you're doing with the data, you may need to first cast it to an array or list so that NHibernate doesn't try to do any funny stuff with your operations.
I've used Entity Framework for years and I'm well familiar with this, and I've only used NHibernate a little bit, but the two tools appear to be similar in this regard.
Related
Having failed to find a satisfying solution, let me post this here:
We're using NHibernate as our ORM and are just beginning to use Sql Server temporal tables. We therefore need some kind of extension to IQueryable (or the HQL Builder or an InterceptingProvider or something) that will allow us to add the "AS OF" clause to our queries, something like
var results = session.Query<Company>
.Where(c => c.Name == "FogCreek")
.AsOf(DateTime.Today.AddYears(-1));
I've been struggling with it too and gave up as I lost too much time trying to find better approach...
So far I've injected FOR SYSTEM_TIME AS OF into SQL using custom HqlGeneratorForMethod but this gave me invalid SQL expression. So I had to fix it in OnPrepareStatement. This is hacky and not elegant solution but works for most simple cases.
Please look at my solution here and feel free to reply if you find better solution
Ayende describes a really great way to get page count, and a specific page of data in a single query here:
http://ayende.com/blog/2334/paged-data-count-with-nhibernate-the-really-easy-way
His method looks like:
IList list = session.CreateQuery("select b, rowcount() from Blog b")
.SetFirstResult(5)
.SetMaxResults(10)
.List();
The only problem is this example is in HQL, and I need to do the same thing in an ICriteria query. To achieve the equivalent with ICriteria, I need to do something like:
IList list = session.CreateCriteria<Blog>()
.SetFirstResult(5)
.SetMaxResults(10)
.SetProjection(Projections.RootEntity(), Projections.SqlFunction("rowcount", NHibernateUtil.Int64))
.List();
The problem is there is no such thing as Projections.RootEntity(). Is there any way to select the root entity as one of the projections in a projection list?
Yes, I know I could just use CriteriaTransform.TransformToRowCount() but that would require executing the query twice - once for the results and once for the row count. Using Futures may help a little by reducing it to one round-trip, but it's still executing the query twice on the SQL Server. For intensive queries this is unacceptable. I want to avoid the overhead, and return the row count and the results in the same query.
The basic question is: using ICriteria, is there any way to select the root entity AND some other projection at the same time?
EDIT: some related links:
https://nhibernate.jira.com/browse/NH-1372?jql=text%20~%20%22entity%20projection%22
https://nhibernate.jira.com/browse/NH-928
I implemented a RootEntityProjection. You can try the code, which you can find at: http://weblogs.asp.net/ricardoperes/archive/2014/03/06/custom-nhibernate-criteria-projections.aspx.
Let me know if it helped.
Is is possible to add a comment to generated by queryover query in Visual Studio's output?
Previously when we were using ICriteria, there was simple SetComment method and we could set the query name so it was much easier to find specific query in output full of long (almost the same) queries. If it is possible we would prefere to add such comments without converting query to ICriteria.
I don't think there is a direct way of doinf it, but you can try with:
QueryOver<Entity>()
.Where(...
.UnderlyingCriteria.SetComment("....")
do you know anything about Hibernate and its ability to generate dynamic sql queries with HQL?
I you have any links I would appreciate posting, I can't find nothing about it in Hibernate`s documentation.
Best regards
Gabe
//edit
so maybe I will precise what I mean. I am wondering if some HQL code generates SQL queries which uses something like EXECUTE (for postgres)
Not sure what you're aiming for here? HQL in Hibernate will always generate SQL, and you can put your HQL together differently based on input. It will always generate new SQL for each permutation and run. You can make Hibernate precompile/cache queries but that's just a performance optimization and shouldn't be your first concern.
I would also consider looking into the Criteria API which lets you stay a lot more object oriented instead of working with tons of strings.
If you're talking about static queries using dynamic arguments, the syntax is
select f from Foo f where f.bar = ? and f.zim = ?
or, with named parameters
select f from Foo f where f.bar = :bar and f.zim = :zim
If you're talking about completely dynamically created queries based on a set of criteria, then the API to use is... the Criteria API.
Both are largely covered in the Hibernate reference documentation.
I'm trying to reproduce the HqlQuery style 'select new ObjectToProjectOut' functionality. i.e. take a list of columns returned from a query and return as a list of ObjectToProjectOut types that are instantiated using a Constructor with as many parameters as the columns in the query.
This is in effect what 'select new ObjectToProjectOut' achieves in Hql.... but clearly that's not available in SqlQuery. I think I need to set a result transform and use either PassThroughResultTransformer, DistinctRootEntityResultTransformer etc to get it to work.
Anyone know what I should use ?
ok.... after looking at the NHibernate code it seems that I was looking for AliasToBeanConstructorResultTransformer.... of course!
However I may have found an nHibernate bug. If you have the same column name returned twice from two different tables (market.name and account.name, say) then by the time nHibernate returns the array from the db to the transformer, the first occurance of 'Name' will be used for both. Nasty.
Work around is to uniquely alias. With Hql, the sql generated is heavily aliased, so this is only a bug with SqlQuery.
Grrrr. Today must be my day, also found another nHibernate bug/issue I've posted to StackOverflow for comment.
You could use the AddEntity method to fill entities from a SQL query.
Here are two examples from the NHibernate docs:
sess.CreateSQLQuery("SELECT * FROM CATS")
.AddEntity(typeof(Cat));
sess.CreateSQLQuery("SELECT ID, NAME, BIRTHDATE FROM CATS")
.AddEntity(typeof(Cat));