Is there a way to achieve SQL like this with NHibernate ICriteria or QueryOver?
select *
from [BlogPost] b
inner join (select blogpost_id, count(*) matchCount
from [Tag]
where name in ('tag X', 'tag Y')
group by blogpost_id
) tagmatch
on tagmatch.blogpost_id = b.Id
order by tagmatch.matchCount desc
The aim is to rank blog posts by the number of matching tags so that a post with both tag X and tag Y comes above posts with just tag X.
I've got this so far:
DetachedCriteria
.For<Tag>("tag")
.Add(Restrictions.In(Projections.Property<Tag>(x => x.Name), tags.ToArray()))
.SetProjection(Projections.Group<Tag>(t => t.BlogPost))
.CreateCriteria("BlogPost")
.SetFetchMode("BlogPost", FetchMode.Eager)
.AddOrder(Order.Desc(Projections.RowCount()));
However, the resulting query doesn't join fetch BlogPost. Instead it returns just the ids, which leads to select n+1 when the BlogPosts are iterated.
public class BlogPost
{
...
ISet<Tag> Tags {get; set;}
}
public class Tag
{
BlogPost BlogPost { get; set; }
string Name { get; set; }
}
This looks like a similar issue.
Is this now possible with NHibernate 3?
If not, is there an alternative solution?
I can change schema & domain model if necessary. I don't want to use SQL or HQL if possible.
I know this question was put some time ago, but I want to do about the same thing, please take a look to my question here, and this guy here, maybe you can use the idea.
Related
How to setup NHibernate criteria to perform such query?
SELECT
COUNT(1) AS CNT,
l.CAMPAIGN_ID AS CAMPAIGN_ID,
MAX(mc.NAME) AS CAMPAIGN_NAME
FROM
SA_LEADS l
INNER JOIN
SA_CAMPAIGNS mc
ON
l.CAMPAIGN_ID = mc.ID
GROUP BY
CAMPAIGN_SOURCED_ID
ORDER BY
CNT DESC
I have mappings for both tables SA_LEADS and SA_CAMPAIGNS.
For me I would start with the element that I am trying to group by so I would start with a
base of campaign. I can't tell from your query but I would assume that your mappings have a way of moving from campaign to sales lead. I have assumed this is called "SALES_LEAD_LIST"
I also like to make a small class to receive the projection result so would create something to hold the result.
public class CAMPAIGN_PERFORMANCE
{
public CAMPAIGN_PERFORMANCE() {}
public int CP_ID {get; set;}
public string CP_NAME {get; set;}
public int CP_NO_OF_SALES_LEADS {get; set;}
}
Once you have something to put your projection result in you can create a standard criteria and just push it into you new class through a projection
ICriteria criteria = base.Session.CreateCriteria(typeof(SA_CAMPAIGNS));
criteria.CreateAlias("SALES_LEADS_LIST", "SA_LEADS", JoinType.InnerJoin);
criteria.SetProjection(Projections.ProjectionList()
.Add(Projections.Property("ID"), "CP_ID")
.Add(Projections.Property("CAMPAIGN_NAME"), "CP_NAME")
.Add(Projections.CountDistinct("SA_LEADS.ID"), "CP_NO_OF_SALES_LEADS")
.Add(Projections.GroupProperty("ID"));
.Add(Projections.GroupProperty("CAMPAIGN_NAME")));
IList<CAMPAIGN_PERFORMANCE> cpProjections = criteria
.SetResultTransformer(
new AliasToBeanResultTransformer(typeof(CAMPAIGN_PERFORMANCE)))
.List<CAMPAIGN_PERFORMANCE>();
I have two entities, Location and Industry, and a link-table between them. I've configured a many-to-many relationship, in both directions, between the two entities.
In a search query, I'm trying to select Locations that are associated with a list of industries.
After days and days of trying to wrangle the criteria API, I've decided to drop down to HQL and abandon the criteria API. But even that isn't going well for me - it seems, regardless of whether I hand-write this HQL query, or let the criteria API do it, I end up with the same result.
I managed to produce the right result in two ways - like this:
var q = Data.Query("select distinct loc from Location loc join loc.Industries ind where ind in (:ind)");
q.SetParameterList("ind", new Industry[] { Data.GetIndustry(4), Data.GetIndustry(5) });
And (better) like that:
var q = Data.Query("select distinct loc from Location loc join loc.Industries ind where ind.id in (:ind)");
q.SetParameterList("ind", new int[] { 4, 5 });
Unfortunately, both result in a sub-optimal query:
select distinct
location0_.Id as Id16_,
location0_.Name as Name16_,
(etc.)
from Location location0_
inner join LocationIndustry industries1_
on location0_.Id=industries1_.LocationId
inner join Industry industry2_
on industries1_.IndustryId=industry2_.Id
where
industry2_.Id in (? , ?)
Why the extra join?
Is NH not smart enough to know that the Industry.Id property, being the only Industry-property involved in the query, is stored in the LocationIndustry link-table, and there is no need for the extra join to the Industry table itself?
Or am I doing something wrong?
Ideally, the most intuitive thing for me would be to write:
from Location loc where loc.Industries in (:ind)
This does not work - it throws an error and says it does not know about the Industries property. I guess because Industries, being a "property" in programming terms, is actually a "relationship" in terms of DBMS.
What is the simplest and most efficient way to write this query in HQL?
Thanks!
I'm not sure you can avoid this extra join given the mapping strategy you have used.
You could avoid it by using an intermediary class but this would mean you would need a class structure like this:
public class Industry {
//Other stuff
public virtual List<LocationIndustry> LocationIndustries {get; set:;}
}
public class LocationIndustry {
public virtual Location Location {get; set;}
public virtual Industry Industry {get; set;}
}
public class Location {
//normal stuff
public virtual IList<LocationIndustry> LocationIndustries {get; set;}
}
Then you can query on the LocationIndustry class and avoid the join to Location.
I’m having a problem with translating T-SQL query into Nhibernate query – or writing query that will return same results but will be properly written in NH query language (HQL, Criteria, QueryOver, LINQ – I don’t truly care).
I would like to execute similar query from NHibernate:
SELECT
lic.RegNo,
lic.ReviewStatus
FROM
Licence lic
WHERE
lic.RegNo IN
(
SELECT
grouped.RegNo
FROM
(
SELECT
g.[Type],
g.Number,
MAX(g.Iteration) AS [Iteration],
MAX(g.RegNo) AS [RegNo]
FROM
Licence g
GROUP BY
g.[Type],
g.Number
) as grouped
)
ORDER BY
lic.RegNo desc
It returns the top most licenses and fetch their review status if exists. RegNo is created from Type, Number and Iteration (pattern: {0}{1:0000}-{2:00}). Each license can have multiply iterations and some of them can contains ReviewStatus, for instance:
W0004-01 NULL
W0001-03 1
P0004-02 3
P0001-02 4
If iteration part is greater than 1 it means that there are multiply iterations (n) for specific licence.
I’ve manage to create NH query by going twice to database:
LicenceInfoViewModel c = null;
var grouped = session.QueryOver<Licence>()
.SelectList(l => l
.SelectGroup(x => x.Type)
.SelectGroup(x => x.Number)
.SelectMax(x => x.Iteration)
.SelectMax(x => x.RegNo).WithAlias(() => c.RegNo)
).TransformUsing(Transformers.AliasToBean<LicenceInfoViewModel>())
.Future<LicenceInfoViewModel>();
var proper = session.QueryOver<Licence>()
.Select(x => x.RegNo, x => x.ReviewStatus)
.WhereRestrictionOn(x => x.RegNo)
.IsIn(grouped.Select(x => x.RegNo).ToArray())
.TransformUsing(Transformers.AliasToBean<LicenceInfoViewModel>())
.List<LicenceInfoViewModel>();
// ...
public class LicenceInfoViewModel
{
public string RegNo { get; set; }
public LicReviewStatus? ReviewStatus { get; set; }
}
public enum LicReviewStatus
{
InProgress,
Submitted,
Validated,
RequestForInformation,
DecissionIssued
}
However this solution is not good as it require to download all grouped licences from database, and there could be a thousands of them.
Is there a better way to write this query or is there a way to translate provided above T-SQL query into NHibernate?
adding nhibernate and hibernate tags as IMO if this can be done in hibernate it should be easily translated into nh
I don't think that SQL does what you think it does. Iteration is not used for anything.
In any case, it seems unnecessary. You can change the WHERE to the following, and you'll have both valid SQL and HQL:
lic.RegNo IN
(
SELECT
MAX(g.RegNo)
FROM
Licence g
GROUP BY
g.Type,
g.Number
)
public class City
{
virtual public long Id { get; set; }
virtual public string Name { get; set; }
}
City table contains duplicated Names and I want to remove duplicates. I also want the results to be ordered by Id.
First I thought about the following query.
select distinct Name from City order by Id;
But this breaks with 'ORDER BY items must appear in the select list if SELECT DISTINCT is specified.' exception. After seeing http://weblogs.sqlteam.com/jeffs/archive/2007/12/13/select-distinct-order-by-error.aspx I think I should do:
select Name from City group by Name order by min(Id)
So my question is how can I do this query with QueryOver?
This is possible in ICriteria:
var list =
session.CreateCriteria<City>()
.SetProjection(Projections.Group("Name"))
.AddOrder(Order.Asc(Projections.Min("Id")))
.List<string>();
But this is not currently possible in QueryOver, because the .OrderBy(IProjection) overload is missing. Once the missing overload has been added it should look something like:
var list =
s.QueryOver<City>()
.Select(Projections.Group<City>(p => p.Name))
.OrderBy(Projections.Min<City>(c => c.Id)).Asc
.List<string>();
Note that the Projections overloads are there just now, so you can write the following (typesafe) query in ICriteria:
var list =
session.CreateCriteria<City>()
.SetProjection(Projections.Group<City>(c => c.Name))
.AddOrder(Order.Asc(Projections.Min<City>(c => c.Id)))
.List<string>();
So, what I've found is pretty simple...
var query = session.QueryOver<MyModel>()
// Conditions here
.OrderBy(m => m.GetThisDistinctField).Desc() // ...or Asc()...
.SelectList(m => m.SelectGroup(g => g.GetThisDistinctField));
var result = query.List<FieldDataType>().ToList();
return result;
To get an ordered query in queryover, start with a query that includes whatever criteria you need, but then add the SelectList/SelectGroup setup in order to get the distinct list. In other words, it's sort of like NHibernate can take a regular query, and then do special stuff to make it a select distinct query.
This is a solution I'm using in a current project I'm working on; I hope it helps someone else too.
I have a nHibernate query like this
ICriteria query = session.CreateCriteria(typeof(MyResult))
.Add(Expression.Eq("ResultTypeId", myResult.ResultTypeId))
Problem is that users add results all the time and I want to show a table of all the latest results for all the diferent ResultTypes I have.
The MyResult class has a property ResultDate. My question is, what do I add to the query to get it to only return the latest result for the given result type. There is nothing to say that the results will be in date order in the database.
Thanks,
Mark
You can order the result by ResultDate using the AddOrder method, as below:
ICriteria query = session.CreateCriteria(typeof(MyResult))
.Add(Expression.Eq("ResultTypeId", myResult.ResultTypeId))
.AddOrder(Order.Desc("ResultDate"))
.List<MyResult>();
If you want to limit the number of MyResult instances you get back, you can use the SetMaxResults method, like so:
ICriteria query = session.CreateCriteria(typeof(MyResult))
.Add(Expression.Eq("ResultTypeId", myResult.ResultTypeId))
.AddOrder(Order.Desc("ResultDate"))
.SetMaxResults(20)
.List<MyResult>();
If I understand the question well, Mark wants to see an overview of all the last results for each type.
Which means that, for every result type, he only wants to see only one row, and that is the Result which has last been added for that type.
I think that, the easiest way to achieve this, would be to create an additional class, which we can call 'MyResultOverview' for instance:
public class MyResultOverview
{
public int ResultId {get; set;}
public int ResultTypeId {get; set;}
public DateTime ResultDate {get; set;}
}
This class should not be mapped, but NHibernate should be aware that this class exists. Therefore, we'll have to import it:
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" >
<import class="MyResultOverview" />
</hibernate-mapping>
Then, we can create an ICriteria which will populate instances of MyResultOverview (and which will also generate the most efficient SQL Query in order to get this overview).
It should look something like this:
ICriteria criteria = session.CreateCritera (typeof(MyResult));
criteria.SetProjection (Projections.ProjectionList ()
.Add (Projections.Property("Id"), "ResultId")
.Add (Projections.Property("ResultType"), "ResultType")
.Add (Projections.Max("ResultDate"), "ResultDate"));
criteria.SetResultTransformer (Transformers.AliasToBean (typeof(MyResultOverview)));
IList<MyResultOverview> results = criteria.List<MyResultOverview>();
This should give you a list of MyResultOverview instances which represent the MyResults that you're looking for.
Then, in order to retrieve the MyResult itself, you can simply do this by retrieving the MyResult instance for that particalur ResultId that you've retrieved as well.
I haven't tested this, nor did i compile it, but this is the path that I would follow to achieve this.
Order by ResultDate (descending) and select top whatever you feel appropriate.
In HQLthis might work:
select item, tag
from MyItem item
join item.Tags tag
where tag.Id = (
select max(tag2.Id)
from MyItem item2
join item2.Tags tag2
where item2.Id = item.Id
group by item2.Id
)