I'm working with the criteria API, querying against a mapping file that I cannot really change. There is a root entity with many child entities joined to it and certain queries have required us to add
criteria.SetResultTransformer(CriteriaSpecification.DistinctRootEntity);
in order to avoid getting duplicate entities when there are multiple SQL result-lines due to the joins. The problem is that now I also want to apply an alias-to-bean transformer, like so:
criteria.SetResultTransformer(Transformers.AliasToBean(typeof(MyDto)));
Using either one of these works great. However, I need to combine them: I want to load only the required columns into a DTO object, and also get only distinct root entities. How can I do this?
To load only required column into DTO you can use projection with DistinctEntityRootTransformer as follows
ICriteria criteria = session.CreateCriteria(typeof(YourEntity));
criteria.SetProjection(
Projections.Distinct(Projections.ProjectionList()
.Add(Projections.Alias(Projections.Property("Property"), "Property")));
criteria.SetResultTransformer(
new NHibernate.Transform.AliasToBeanResultTransformer(typeof(MyDto)));
IList list = criteria.List();
Related
I'm wondering if there is a simple way to get an ID list of all the target objects relating to a source object in a coldfusion component using ORM?
I can see that you can do a collection mapping for one-to-many relationships, but I am using many-to-many relationships. I don't want to have to get the array of objects and then loop over it to get each id.
Is there any built in function or property that could do this?
I think something like the code sample below is a little too heavy since it is getting the whole query and then getting a single column from it.
valuelist( EntityToQuery( object.getRelationalFields() ).id )
Sometimes it doesn't make sense to use ORM, and this is the time. Use the good old <cfquery> for this!
I think ORMExecuteQuery may work for you, something like this:
result = ORMExecuteQuery("select id from Model as m where m.parent.id = :id", {id = 123});
Actual clause format depends on the relationship definition.
In a result you'll have the array of model PKs.
I have a table, CityComplete, with columns "USPSCITY", "STATE" and "ZIPCODE"
I have an existing SQLQuery that distinctly selects USPSCITY and STATE based on a fuzzy search. However, when I call list() I get an exception:
19. ResultSet.getString(ZIPCODE)
java.sql.SQLException: Column 'ZIPCODE' not found.
The SQLQuery's entity is set to the CityComplete object.
Is there any way to have Hibernate not try and get ZIPCODE, or have it be part of the result set in some way?
What's the best way to resolve this, other than using Criteria, setting a virtual column with null data, or just getting a full result set and handling distinction on the code side?
When you perform a regular Hibernate query (HQL or Criteria), Hibernate will try to map the resultset based on the properties of the entities which you specified in the mapping. If you are not bringing the "promised" data from the database, you'll need to handle the mapping by yourself, using a ResultTransformer. In this case, you'd still use your CityComplete, but they will be without a ZIPCODE. Unfortunately, there's not much documentation about how to use a ResultTransformer, but you can take a look at the Hibernate's JavaDoc and see if there's one that you could use. If not, you'd need to implement your own:
http://docs.jboss.org/hibernate/core/3.6/javadocs/org/hibernate/transform/ResultTransformer.html
I have a number of database table that looks like this:
EntityId int : 1
Countries1: "1,2,3,4,5"
Countries2: "7,9,10,22"
I would like to have NHibernate load the Country entities identifed as 1,2,3,4,5,7,9 etc. whenever my EntityId is loaded.
The reason for this is that we want to avoid a proliferation of joins, as there are scores of these collections.
Does fetching the countries have to happen as the entity is loaded - it is acceptable that you run a query to fetch these? (You could amend your DAO to run the query after fetching the entity.) The reason I ask is that simply running a query compared to having custom code invoked when entities are loaded requires less "plumbing" and framework innards.
After fecthing your entity, and you have the Country1,Country2 lists, You can run a query like:
select c from Country c where c.id in (:Country1)
passing :Country1 as a named parameter. You culd also retrieve all rows for both sets of countries
select Entity e where e.id in (:Country1, :Country2)
I'm hoping the country1 & country2 strings can be used as they are, but I have a feeling this won't work. If so, you should convert the Strings to a collection of Integers and pass the collection as the query parameter.
EDIT: The "plumbing" to make this more transparent comes in the form of the IInterceptor interface. This allows you to plug in to how entities are loaded, saved, updated, flushed etc. Your entity will look something like this
class MyEntity
{
IList<Country> Country1;
IList<Country> Country2;
// with public getter/setters
String Country1IDs;
String Country2IDs;
// protected getter and setter for NHibernate
}
Although the domain object has two representations of the list - the actual entities, and the list of IDs, this is the same intrusion that you have when declaring a regular ID field in an entity. The collections (country1 and Country2) are not persisted in the mapping file.
With this in place, you provide an IInterceptor implementation that hooks the loading and saving. On loading, you fetch the value of the countryXID property an use to load the list of countries (as I described above.) On saving, you turn the IList of countries into an ID list, and save this value.
I couldn't find the documentation for IInterceptor, but there are many projects on the net using it. The interface is described in this article.
No you cannot, at least not with default functionality.
Considering that there is no SPLIT string function in SQL it would be hard for any ORM to detect the discreet integer values delimited by commas in a varchar column. If you somehow (custom sql func) overcame that obstacle, your best shot would be to use some kind of component/custom user type that would still make a smorgasbond of joins on the 'Country' table to fetch, in the end, a collection of country entities...
...but I'm not sure it can be done, and it would also mean writing from scratch the persistence mechanism as well.
As a side note, I must say that i don't understand the design decision; you denormalized the db and, well, since when joins are bad?
Also, the other given answer will solve your problem without re-designing your database, and without writing a lot of experimental plumbing code. However, it will not answer your question for hydration of the country entities
UPDATE:
on a second thought, you can cheat, at least for the select part.
You could make a VIEW the would split the values and display them as separate rows:
Entity-Country1 View:
EntityId Country
1 1
1 2
1 3
etc
Entity-Country2 View:
EntityId Country
1 7
1 9
1 10
etc
Then you can map the view
I am fairly new to nHibernate and DDD, so please bear with me.
I have a requirement to create a new report from my SQL table. The report is read-only and will be bound to a GridView control in an ASP.NET application.
The report contains the following fields Style, Color, Size, LAQty, MTLQty, Status.
I have the entities for Style, Color and Size, which I use in other asp.net pages. I use them via repositories. I am not sure If should use the same entities for my report or not. If I use them, where I am supposed to map the Qty and Status fields?
If I should not use the same entities, should I create a new class for the report?
As said I am new to this and just trying to learn and code properly.
Thank you
For reports its usually easier to use plain values or special DTO's. Of course you can query for the entity that references all the information, but to put it into the list (eg. using databinding) it's handier to have a single class that contains all the values plain.
To get more specific solutions as the few bellow you need to tell us a little about your domain model. How does the class model look like?
generally, you have at least three options to get "plain" values form the database using NHibernate.
Write HQL that returns an array of values
For instance:
select e1.Style, e1.Color, e1.Size, e2.LAQty, e2.MTLQty
from entity1 inner join entity2
where (some condition)
the result will be a list of object[]. Every item in the list is a row, every item in the object[] is a column. This is quite like sql, but on a higher level (you describe the query on entity level) and is database independent.
Or you create a DTO (data transfer object) only to hold one row of the result:
select new ReportDto(e1.Style, e1.Color, e1.Size, e2.LAQty, e2.MTLQty)
from entity1 inner join entity2
where (some condition)
ReportDto need to implement a constructor that has all this arguments. The result is a list of ReportDto.
Or you use CriteriaAPI (recommended)
session.CreateCriteria(typeof(Entity1), "e1")
.CreateCriteria(typeof(Entity2), "e2")
.Add( /* some condition */ )
.Add(Projections.Property("e1.Style", "Style"))
.Add(Projections.Property("e1.Color", "Color"))
.Add(Projections.Property("e1.Size", "Size"))
.Add(Projections.Property("e2.LAQty", "LAQty"))
.Add(Projections.Property("e2.MTLQty", "MTLQty"))
.SetResultTransformer(AliasToBean(typeof(ReportDto)))
.List<ReportDto>();
The ReportDto needs to have a proeprty with the name of each alias "Style", "Color" etc. The output is a list of ReportDto.
I'm not schooled in DDD exactly, but I've always modeled my nouns as types and I'm surprised the report itself is an entity. DDD or not, I wouldn't do that, rather I'd have my reports reflect the results of a query, in which quantity is presumably count(*) or sum(lineItem.quantity) and status is also calculated (perhaps, in the page).
You haven't described your domain, but there is a clue on those column headings that you may be doing a pivot over the data to create LAQty, MTLQty which you'll find hard to do in nHibernate as its designed for OLTP and does not even do UNION last I checked. That said, there is nothing wrong with abusing HQL (Hibernate Query Language) for doing lightweight reporting, as long as you understand you are abusing it.
I see Stefan has done a grand job of describing the syntax for that, so I'll stop there :-)
I'm developing a web- application using NHibernate. Can you tell me how to write a NHibernate Query for the following SQL query:
SELECT v1.Id
FROM VIEW v1
LEFT JOIN VIEW v2 ON v1.SourceView = v2.Id
ORDER BY v1.Position
It's basically a auto-join but I don't know how to write this in Nhibernate. Lets say the property names are the same as the table column names.
You could just perform the select on the original entity and make the association between the two objects "lazy = false". As long as the entities are mapped then both will be returned and you wont get a lazyloadingexception when trying to access the object.
If you don't want to map "lazy=false" then you can also iterate through the results and perform some sort of operation (such as asking if it is null; if(v1.AssocatedObject == null){}) to ensure the data is loaded while the session is open.
Update:
I think there is actually a better one than that in, NHibernateUtil.Initialise() that can initialise a collection without having to wander through it.