I have a Person class. A person class contains a collection of Friends (also Person objects). A person class also has a LatestLogin property which is the LatestLogin time.
For a given person, I want to return their first 10 friends ordered by descending LatestLogin.
HQL I can do no problem:
select friends from Person person inner join person.Friends friends where person = :person order by friends.LatestLogin desc
How do I write this in a Criteria Query? I don't want the containing person object, just a List of the person's friends ordered by LatestLogin.
Here it is:
var cachedPosts = Session.CreateCriteria<Person>("main")
.CreateCriteria("Friends", "f")
.Add(Restrictions.Eq("f.Id", person.ID))
.AddOrder(Order.Desc("main.LatestLogin"))
.List<Person>();
Related
I have 2 nodes:
Students and Subjects.
I want to be able to add multiple student names to multiple subjects at the same time using cypher query.
So far I have done it by iterating through the list of names of students and subjects and executing the query for each. but is there a way to do the same in the query itself?
This is the query I use for adding 1 student to 1 subject:
MATCH
(s:Student)-[:STUDENT_BELONGS_TO]->(c:Classroom),
(u:Subjects)-[:SUBJECTS_TAUGHT_IN]->(c:Classroom)
WHERE
s.id = ${"$"}studentId
AND c.id = ${"$"}classroomId
AND u.name = ${"$"}subjectNames
AND NOT (s)-[:IN_SUBJECT]->(u)
CREATE (s)-[:IN_SUBJECT]->(u)
So I want to be able to receive multiple subjectNames and studentIds at once to create these connections. Any guidance for multi relationships in cypher ?
I think what you are looking for is UNWIND. If you have an array as parameter to your query:
studentList :
[
studentId: "sid1", classroomId: "cid1", subjectNames: ['s1','s2'] },
studentId: "sid2", classroomId: "cid2", subjectNames: ['s1','s3'] },
...
]
You can UNWIND that parameter in the beginning of your query:
UNWIND $studentList as student
MATCH
(s:Student)-[:STUDENT_BELONGS_TO]->(c:Classroom),
(u:Subjects)-[:SUBJECTS_TAUGHT_IN]->(c:Classroom)
WHERE
s.id = student.studentId
AND c.id = student.classroomId
AND u.name = in student.subjectNames
AND NOT (s)-[:IN_SUBJECT]->(u)
CREATE (s)-[:IN_SUBJECT]->(u)
You probably need to use UNWIND.
I haven't tested the code, but something like this might work:
MATCH
(s:Student)-[:STUDENT_BELONGS_TO]->(c:Classroom),
(u:Subjects)-[:SUBJECTS_TAUGHT_IN]->(c:Classroom)
WITH
s AS student, COLLECT(u) AS subjects
UNWIND subjects AS subject
CREATE (student)-[:IN_SUBJECT]->(subject)
Using these tables:
*student {'s_id','s_name,'...} , class {'c_id','c_name',...} student2class {'s_id','c_id'}, grades {'s_id','c_id','grade'}*
Is it possible to perform a query (nested query?) put class name as subtitle and then all students (of that class) and grades, next class name as subtitle ...
The result I need is:
Maths
John .... C
Anna .... B
[...]
Biology
Anna .... C
Jack .... A
[...]
For each row from class I'll have a subquery fetching all data related with this class
No need of any sub-query. You can get your data this way:
SELECT c_name, s_name_, grade
FROM student, class, grades
WHERE student.s_id = grades.s_id and class.c_id = grades.c_id
ORDER BY c_name
The presentation of results depends on your system/tools, as others already said. This is a link to the solution for Microsoft Access:
http://office.microsoft.com/en-001/access-help/create-a-grouped-or-summary-report-HA001159160.aspx
The solution should be implemented in your client side code and not in the database. From database you should just get a simple table formatted data (subject, student, grade)
Then convert the above recordset to the format you want:
For an example in C# you could convert the recordset into lookup
var Lookup = DataSet.Tables[0].Rows.ToLookup(x => x["subjectColumn"]);
now you can loop through the lookup and format your result
foreach (var grade in Lookup)
{
subject = grade.Key;
...
}
I'm struggling with following scenario: Let's assume I have the two entities Classroom and Member, mapped with many-to-many. Classroom has the collection Members, containing the entities Member.
I would like to get the classrooms which do have members of a certain count. That would result in something like:
FROM Classroom cr WHERE cr.Members.size < 10
Now I have a Type on Classroom. I'd like to filter first on Type, then the size. This won't work:
FROM Classroom cr WHERE cr.Members.size < 10 AND cr.Members.Type = 1
Results in: illegal attempt to dereference collection
How could I write such a query?
I would imagine you need to do a join
from Classroom as cr left join cr.Members as m
where cr.Members.size < 10 and m.Type = 1
I have a simple test object model in which there are schools, and a school has a collection of students.
I would like to retrieve a school and all its students who are above a certain age.
I carry out the following query, which obtains a given school and the children which are above a certain age:
public School GetSchoolAndStudentsWithDOBAbove(int schoolid, DateTime dob)
{
var school = this.Session.CreateCriteria(typeof(School))
.CreateAlias("Students", "students")
.Add(Expression.And(Expression.Eq("SchoolId", schoolid), Expression.Gt("students.DOB", dob)))
.UniqueResult<School>();
return school;
}
This all works fine and I can see the query going to the database and returning the expected number of rows.
However, when I carry out either of the following, it gives me the total number of students in the given school (regardless of the preceding request) by running another query:
foreach (Student st in s.Students)
{
Console.WriteLine(st.FirstName);
}
Assert.AreEqual(s.Students.Count, 3);
Can anyone explain why?
You made your query on the School class and you restricted your results on it, not on the mapped related objects.
Now there are many ways to do this.
You can make a static filter as IanL said, however its not really flexible.
You can just iterate the collection like mxmissile but that is ugly and slow (especially considering lazy loading considerations)
I would provide 2 different solutions:
In the first you maintain the query you have and you fire a dynamic filter on the collection (maintaining a lazy-loaded collection) and doing a round-trip to the database:
var school = GetSchoolAndStudentsWithDOBAbove(5, dob);
IQuery qDob = nhSession.CreateFilter(school.Students, "where DOB > :dob").SetDateTime("dob", dob);
IList<Student> dobedSchoolStudents = qDob.List<Student>();
In the second solution just fetch both the school and the students in one shot:
object result = nhSession.CreateQuery(
"select ss, st from School ss, Student st
where ss.Id = st.School.Id and ss.Id = :schId and st.DOB > :dob")
.SetInt32("schId", 5).SetDateTime("dob", dob).List();
ss is a School object and st is a Student collection.
And this can definitely be done using the criteria query you use now (using Projections)
Unfortunately s.Students will not contain your "queried" results. You will have to create a separate query for Students to reach your goal.
foreach(var st in s.Students.Where(x => x.DOB > dob))
Console.WriteLine(st.FirstName);
Warning: That will still make second trip to the db depending on your mapping, and it will still retrieve all students.
I'm not sure but you could possibly use Projections to do all this in one query, but I am by no means an expert on that.
You do have the option of filtering data. If it there is a single instance of the query mxmissle option would be the better choice.
Nhibernate Filter Documentation
Filters do have there uses, but depending on the version you are using there can be issues where filtered collections are not cached correctly.
I'm having difficulties with multiple joins in the NHibernate Criteria search. Say I had a pet table, and I wanted to return all pets where the pet category was Dog, and the owner gender was female, ordered by the pet birthday. I've tried a bunch of permutations for how I can get this but haven't been able to figure it out. My latest iteration is as follows:
var recentPets = session.CreateCriteria(typeof(Pet))
.AddOrder(Order.Desc("PetBirthday"))
.CreateCriteria("PetType", "pt", JoinType.InnerJoin)
.CreateCriteria("PetOwnerId", "po", JoinType.InnerJoin)
.Add(Expression.Eq("pt.PetTypeName", petType))
.Add(Expression.Eq("po.PersonGender", gender))
.List<Pet>();
Thanks so much for the help!
Is there a reason you are not using the Hibernate/Java persistence query language to perform the query?
select p from Pet p
join p.owner o
where o.gender = :gender
and p.type.name = :petType
order by p.birthday