I have the following question/problem:
I'm using JPQL (JPA 2.0 and eclipselink) and I wanna create a query that gives me the results sorted the following way:
At first the results sorted ascending by the best matches. After that should appear the inferior matches.
My objects are based on a simple class called 'Person' with the attributes:
{String Id,
String forename,
String name}
For example if I'm searching for "Picol" the result should look like:
[{129, Picol, Newman}, {23, Johnny, Picol},{454, Picolori, Newta}, {4774, Picolatus, Larimus}...]
PS: I already thought about using two queries, the first is searching with "equals" and the second with "like", although I'm not quite sure how to connect both queryresults...?
Hope for your help and thanks in advance,
Florian
If, as your question seem to imply, you only have two groups (first group : forename or name equals searched string; second group : forename or name contains searched string), and if all the persons of a given group have the same "match score", then using two queries is indeed a good solution.
First query :
select p from Person p where p.foreName = :param or p.name = :param
Second query :
select p from Person p where (p.foreName like :paramSurroundedWithPercent
or p.name like :paramSurroundedWithPercent)
and p.foreName != :param
and p.name != :param
Execute both queries (each returning a List<Person>), and add all the elements of the second list to the first one (using the addAll() method)
Related
I'm new to Scala and slick. My use case is like this. I have name, school, and gradeList. Name and school are string values. GradeList is a map where i have subject as key and grade as value. I need to write a search query for this scenario. And also name and school columns are in one table and subject and grade columns are in another table. So i need to join them too. I can make the query work when a string value is given for subject and grade. But I cannot figure out a way to iterate through the map where all the subject, grade key pair is considered for the query.
So far my code is as below.
val innerJoin = for {
(a, _) <- nameQuery.join(gradeQuery).on(_.id === _.studentId)
.filter(result =>
(result._1.name.toLowerCase.like(s"%$name%") &&
(result._1.school.toLowerCase.like(s"%$school%") &&
result._2.subject.toLowerCase.like(s"%$subject%") &&
result._2.grade.toLowerCase.like(s"%$grade%"))
} yield a
innerJoin.distinctOn(_.id).take(limit).result
name, school, gradeList are my parameters to the function.
Can someone help me in finding a solution for this? Thanks in advance.
I am experiencing various things while studying JPA, but I am too unfamiliar with it, so I would like to get some advice.
The parts I got stuck in during my study were grouped into three main categories. Could you please take a look at the code below?
#Repository
public interface TestRepository extends JpaRepository<TestEntity,Long> {
#Query(" SELECT
, A.test1
, A.test2
, B.test1
, B.test2
FROM TEST_TABLE1 A
LEFT JOIN TEST_TABLE2 B
ON A.test_no = B.test_no
WHERE A.test3 = ?1 # Here's the first question
if(VO.test4 is not null) AND B.test4 = ?2") # Here's the second question
List<Object[] # Here's the third question> getTestList(VO);
}
First, is it possible to extract test3 from the VO received when using native sql?
Usually, String test1 is used like this, but I wonder if there is any other way other than this.
Second, if extracting is possible in VO, can you add a query in #QUERY depending on whether Test4 is valued or not?
Thirdly, if I use List<Object[]>, can the result of executing a query that is not in the already created entity (eg, test1 in TEST_TABLE2, which is not in the entity of TEST_TABLE1) can be included?,
First, is it possible to extract test3 from the VO received when using native sql? Usually, String test1 is used like this, but I wonder if there is any other way other than this.
Yes, it is possible.
You must use, eg where :#{[0].test3} is equals vo.test3
[0] is position the first param, past for method annotated with #Query
#Query(value = "SELECT a.test1, a.test2, b.test1, b.test2
FROM test_table1 a
LEFT JOIN test_table2 b ON a.test_no = b.test_no
WHERE a.test3 = :#{[0].test3}", nativeQuery = true)
List<Object[]> getList(VO);
Second, if extracting is possible in VO, can you add a query in #QUERY depending on whether Test4 is valued or not?
You can use a trick eg:
SELECT ... FROM table a
LEFT JOIN table b ON a.id = b.id
WHERE a.test3 = :#{[0].test3}
AND (:#{[0].test4} IS NOT NULL AND b.test4 = :#{[0].test4})
Thirdly, if I use List<Object[]>, can the result of executing a query that is not in the already created entity (eg, test1 in TEST_TABLE2, which is not in the entity of TEST_TABLE1) can be included?
Sorry, but I not understand the third question.
Maybe this tutorial will help you: https://www.baeldung.com/jpa-queries-custom-result-with-aggregation-functions
I'm trying make a query with HQL that will stay with the same order as given list of IDs. I know it's possible with SQL but I can't find any way to do it with HQL (and I cannot do it with native SQL because I got many joins)
Example
fingerIds = [3,1,10,4]
SELECT p FROM People p
JOIN FETCH p.fingers f
WHERE f.id IN :fingerIds
DB: PostgreSQL 10.4
Hibernate: 4.3.11.Final
Eg. Given list of IDs: [3,1,10,4]
Actual result's order: [1,3,4,10]
Expected result's order: [3,1,10,4]
You can obtain the order by adding to your query the keyword FIELD, in your example:
SELECT p FROM People p
JOIN FETCH p.fingers f
WHERE f.id IN :fingerIds
ORDER BY FIELD(f.ID,3,1,10,4)
Ofc you can replace the numbers with your variable :fingerIds
You can find more about that command here.
Returns the index (position) of str in the str1, str2, str3, ... list. Returns 0 if str is not found.
I'm using Flask-SQLAlchemy with PostgreSQL. I have the following two models:
class Course(db.Model):
id = db.Column(db.Integer, primary_key = True )
course_name =db.Column(db.String(120))
course_description = db.Column(db.Text)
course_reviews = db.relationship('Review', backref ='course', lazy ='dynamic')
class Review(db.Model):
__table_args__ = ( db.UniqueConstraint('course_id', 'user_id'), { } )
id = db.Column(db.Integer, primary_key = True )
review_date = db.Column(db.DateTime)#default=db.func.now()
review_comment = db.Column(db.Text)
rating = db.Column(db.SmallInteger)
course_id = db.Column(db.Integer, db.ForeignKey('course.id') )
user_id = db.Column(db.Integer, db.ForeignKey('user.id') )
I want to select the courses that are most reviewed starting with at least two reviews. The following SQLAlchemy query worked fine with SQlite:
most_rated_courses = db.session.query(models.Review, func.count(models.Review.course_id)).group_by(models.Review.course_id).\
having(func.count(models.Review.course_id) >1) \ .order_by(func.count(models.Review.course_id).desc()).all()
But when I switched to PostgreSQL in production it gives me the following error:
ProgrammingError: (ProgrammingError) column "review.id" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT review.id AS review_id, review.review_date AS review_...
^
'SELECT review.id AS review_id, review.review_date AS review_review_date, review.review_comment AS review_review_comment, review.rating AS review_rating, review.course_id AS review_course_id, review.user_id AS review_user_id, count(review.course_id) AS count_1 \nFROM review GROUP BY review.course_id \nHAVING count(review.course_id) > %(count_2)s ORDER BY count(review.course_id) DESC' {'count_2': 1}
I tried to fix the query by adding models.Review in the GROUP BY clause but it did not work:
most_rated_courses = db.session.query(models.Review, func.count(models.Review.course_id)).group_by(models.Review.course_id).\
having(func.count(models.Review.course_id) >1) \.order_by(func.count(models.Review.course_id).desc()).all()
Can anyone please help me with this issue. Thanks a lot
SQLite and MySQL both have the behavior that they allow a query that has aggregates (like count()) without applying GROUP BY to all other columns - which in terms of standard SQL is invalid, because if more than one row is present in that aggregated group, it has to pick the first one it sees for return, which is essentially random.
So your query for Review basically returns to you the first "Review" row for each distinct course id - like for course id 3, if you had seven "Review" rows, it's just choosing an essentially random "Review" row within the group of "course_id=3". I gather the answer you really want, "Course", is available here because you can take that semi-randomly selected Review object and just call ".course" on it, giving you the correct Course, but this is a backwards way to go.
But once you get on a proper database like Postgresql you need to use correct SQL. The data you need from the "review" table is just the course_id and the count, nothing else, so query just for that (first assume we don't actually need to display the counts, that's in a minute):
most_rated_course_ids = session.query(
Review.course_id,
).\
group_by(Review.course_id).\
having(func.count(Review.course_id) > 1).\
order_by(func.count(Review.course_id).desc()).\
all()
but that's not your Course object - you want to take that list of ids and apply it to the course table. We first need to keep our list of course ids as a SQL construct, instead of loading the data - that is, turn it into a derived table by converting the query into a subquery (change the word .all() to .subquery()):
most_rated_course_id_subquery = session.query(
Review.course_id,
).\
group_by(Review.course_id).\
having(func.count(Review.course_id) > 1).\
order_by(func.count(Review.course_id).desc()).\
subquery()
one simple way to link that to Course is to use an IN:
courses = session.query(Course).filter(
Course.id.in_(most_rated_course_id_subquery)).all()
but that's essentially going to throw away the "ORDER BY" you're looking for and also doesn't give us any nice way of actually reporting on those counts along with the course results. We need to have that count along with our Course so that we can report it and also order by it. For this we use a JOIN from the "course" table to our derived table. SQLAlchemy is smart enough to know to join on the "course_id" foreign key if we just call join():
courses = session.query(Course).join(most_rated_course_id_subquery).all()
then to get at the count, we need to add that to the columns returned by our subquery along with a label so we can refer to it:
most_rated_course_id_subquery = session.query(
Review.course_id,
func.count(Review.course_id).label("count")
).\
group_by(Review.course_id).\
having(func.count(Review.course_id) > 1).\
subquery()
courses = session.query(
Course, most_rated_course_id_subquery.c.count
).join(
most_rated_course_id_subquery
).order_by(
most_rated_course_id_subquery.c.count.desc()
).all()
A great article I like to point out to people about GROUP BY and this kind of query is SQL GROUP BY techniques which points out the common need for the "select from A join to (subquery of B with aggregate/GROUP BY)" pattern.
I am looking at some EF examples and trying to decipher what 'Query Projection' exactly equates to when doing LINQ to Entities or EntitySQL. I believe it is when the query results are filtered and projected into an anonymous type but not 100% sure.
Can someone please define this and maybe provide a small L2E query that uses an example of it?
Projection is when the result of a query is output to a different type than the one queried. Another article defined it as : the process of transforming the results of a query
Projection can be to an anonymous type, but could also be to a concrete type. If you come from a SQL world, it is akin to the columns listed in your SELECT clause.
Example selecting a sub-set of an object into an concrete type:
ParentObj.Select(x=> new ParentSlim { ParentID = x.ParentID, Name = x.Name } );
.
Example merging to object into a 3rd anonymous type:
Note: the select new portion is the projection.
from P in ParentObj.AsQueryable()
join C in ChildObj.AsQueryable() on P.ParentID == C.ParentID
select new { // <-- look ma, i'm projecting!
ParentID = P.ParentID,
Name = P.Name,
SubName = C.Name
RandomDate = DateTime.UtcNow()
}