Issues with NHibernate QueryOver and Subqueries

Question

I have the following model:

public class User
{
    public virtual int Id { get; set; }
    public virtual string Username { get; set; }
    public virtual string Password { get; set; }
    public virtual string Email { get; set; }
    public IList<SubmissionNote> Notes { get;set; }
}

public class SubmissionNote
{
    public virtual Int64 Id { get; set; }
    public virtual string Text { get; set; }
    public virtual DateTime CreatedOn { get; set; }
    public virtual User Creator { get; set; }
    public virtual Submission BelongsTo { get; set; }
}

public class Submission
{
    public virtual Int64 Id { get; set; }
    public virtual DateTime HappenedOn { get; set; }
    public virtual int StatusCode { get; set; }
}

I would like to write a query that brings all the Submissions whose last note was entered by some user or a list of users (identified by their names). I would appreciate your help for building this query using NHibernate QueryOver API. I have been able to create a query to bring all the last notes as follows:

SubmissionNote alias = null;
var lastNote = session.QueryOver<SubmissionNote>()
    .SelectList(list => list.
        SelectGroup(x => x.BelongsTo).WithAlias(() => alias.BelongsTo).
        SelectMax(x => x.CreatedOn).WithAlias(() => alias.CreatedOn).
        Select(x => x.Creator).WithAlias(() => alias.Creator).
        Select(x => x.Id).WithAlias(() => alias.Id).
        Select(x => x.Text).WithAlias(() => alias.Text))
    .TransformUsing(Transformers.AliasToBean<SubmissionNote>())
    .List();

Can I use the specified query as a subquery to produce the required result? Or do you suggest another solution?

jbl · Accepted Answer · 2013-01-16 13:07:51Z

3

I would try something like this with a subquery (not tested though)

SubmissionNote subNoteAlias = null, subNoteAliasMax =null;
User userAlias = null;
String[] userNames = new[]{"John","Joe"};

var subquery =
    QueryOver.Of(() => subNoteAliasMax)
       .Where(subNote => subNote.BelongsTo.Id == subNoteAlias.BelongsTo.Id)
       .Select(Projections.Max<SubmissionNote>(subNote => subNote.CreatedOn));

var result = session
 .QueryOver<SubmissionNote>(() => subNoteAlias)
 .WithSubquery.WhereProperty(subNote=>subNote.CreatedOn).Eq(subquery)
 .JoinQueryOver(
      subNote=>subNote.Creator
      ,()=>userAlias
      ,JoinType.InnerJoin
      ,Restrictions.In(Projections.Property(() => userAlias.Username ), userNames))
  .List();

The generated SQL query would (very) roughly look like :

SELECT SubmissionNote.*
  FROM SubmissionNote INNER JOIN User
  ON SubmissionNote.creatorId = User.userId
  AND User.userName in ('john','joe')
  WHERE SubmissionNote.CreatedOn = (SELECT MAX(CreatedOn) FROM SubmissionNote snAlias     
     WHERE snAlias.SubmissionId = SubmissionNote.SubmissionId)

Hope this will help. There might be issues with the subquery returning a date instead of an id. LMK and I will give it a look.

edited Jan 16, 2013 at 13:07

answered Jan 16, 2013 at 9:57

jbl

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2 Comments

Ikaso Over a year ago

I tried the query and it seems to work. I am kind of overwhelmed with your query since my intuition told me I will have to use a group by for my task. Can you explain your logic for this query?

jbl Over a year ago

@Ikaso I updated my answer with a sketch of the generated SQL Query. Maybe you can achieve the same result with an intermediate DTO for storing the result of the group by. I would be interested in the answer

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