We are working on a project in school and we trying to use entity JPA.
We have several tables in our Mysql database and the one we are using is taxonomy, term, campaign and term_campaign_relationship.
We have made an entity for campaign, term, and taxonomy. We would like to get all the terms that are related to a campaign and filtered by taxonomy id.
We have used the #ManyToMany JPQL with #JoinTable and joinColumns
With that we have received all the terms that are related with the campaign.
But how do we get the result filtered by the taxonomy id only?
The sql statement below shows the result we are looking for...
SELECT
t.id, t.term_name, t.taxonomy_id
FROM
term t
INNER JOIN
taxonomy ty ON ty.id = t.taxonomy_id
INNER JOIN
campaign c ON c.id IN (SELECT
tc.campaign_id
FROM term_campaign_relationship tc
WHERE tc.term_id = t.id
)
WHERE c.id = 1 AND ty.id = 1;
This is from our campaign entity in java
#ManyToMany()
#JoinTable(
name="term_campaign_relationship",
joinColumns={#JoinColumn(name="campaign_id", referencedColumnName="id")},
inverseJoinColumns={#JoinColumn(name="term_id", referencedColumnName="id")})
private Collection<Term> programTypes;
Please advise if we are missing anything...
Is this the solution you looked for?
Query query = entityManager.createQuery("Select tax from taxonomy tax where tax.id = :arg1");
query.setParameter("arg1", 1);
Related
Here are my entity:
#Entity
public class ProductStateEntity {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id", nullable = false)
private Integer id;
#OneToOne
#JoinColumn(name = "product_id", nullable = false)
private ProductEntity product;
// other fields
}
#Entity
public class ProductEntity {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id", nullable = false)
private Integer id;
// other fields
}
If I make a request this way:
session.get(ProductStateEntity.class, 10);
SQL is formed this way:
SELECT product_states.id, product_states.product_id, products.id, -- other columns
FROM product_states
INNER JOIN products ON product_states.product_id=products.id
WHERE product_states.id=10
So far, so good, using INNER JOIN.
If you make a request in this way:
session.createQuery("from ProductStateEntity where id = :id")
.setParameter("id", 10)
.list()
SQL is formed this way:
SELECT product_states.id, product_states.product_id, -- other columns
FROM product_states
WHERE product_states.id=10;
SELECT products.id, -- other columns
FROM products
WHERE products.id=10
In this case, 2 requests are made. First a query is made in product_states, and then in products.
That's not all, now we will make such a request, which receives 4 records of 4 id at once:
session.createQuery("from ProductStateEntity where id in :ids")
.setParameter("ids", Arrays.asList(10, 11, 12, 13))
.list();
SQL is formed this way:
SELECT product_states.id, product_states.product_id, -- other columns
FROM product_states
WHERE product_states.id IN (10, 11, 12, 13);
SELECT products.id, -- other columns
FROM products
WHERE products.id=10;
SELECT products.id, -- other columns
FROM products
WHERE products.id=11;
SELECT products.id, -- other columns
FROM products
WHERE products.id=12;
SELECT products.id, -- other columns
FROM products
WHERE products.id=13;
In this case, 5 requests are made. First, a request is made in the product_states, the id of all products is obtained, and then it is done on 1 request to receive each of 4 products.
Add join fetch to the previous query:
session.createQuery("from ProductStateEntity p join fetch p.product where p.id in :ids")
.setParameter("ids", Arrays.asList(10, 11, 12, 13))
.list();
SQL is formed this way:
SELECT product_states.id, products.id, product_states.product_id, -- other columns
FROM product_states
INNER JOIN products ON product_states.product_id=products.id
WHERE product_states.id IN (10, 11, 12, 13)
Thus, only 1 request is made with INNER JOIN, which is what I want to achieve.
And so the questions are:
Why do you need to specify join fetch explicitly in createQuery? Could this default behavior be made? After all, a single query with join is better than a lot.
Why, without specifying join fetch, additional select queries are not combined into one with id in (...)? Instead, Hibernate makes selects one at a time. Can this be customized?
n+1 fetching strategy is default one for Hibernate - just because, as stated in documentation
These defaults make sense for most associations in the majority of applications
to change this behaviour globally you can set hibernate.default_batch_fetch_size, and you will find some topics in the internet about how to set proper value and why
And one more thing - it's common opinion that fetch join is a solution for every problem but it's not. We must remember about Cartesian Product Problem.
The fetching strategy depends on how our application works, what's the environment setup (e.g. latency in DB connections), what data model do we use and many many other things. There is no one good solution for everyone, that's why we have many fetching strategies in Hibernate
I have a tables with One-Many Relationships as follows
City->School->Teacher->Children
and my JPQL for retrieving children from a city is as below
#Query("Select c from Children c where c.teacher.school.city=:city")
Set<Children> findChildrenFromCity(#Param("city") City city);
This reference here about Where clause says that
"Compound path expressions make the where clause extremely powerful."
However, upon observing the logs I realise that the above query is doing strange things like
Generate multiple Selects instead of one Select
Some cross joins can be seen in the logs
I am trying to understand if I am defining my query correctly and if the compound Where is indeed so powerful, why is my query so inefficient.
You can use the following method:
Set<Children> findAllByTeacherSchoolCity(String city);
assuming, that your class Children has field Teacher teacher, Teacher has School school and School has String city.
In case there are differences, please ask in comments for clarification.
Try this
#Query("Select c from City city join city.schools s join s.teachers t join t.childrens c where city = :city")
Set<Children> findChildrenFromCity(#Param("city") City city);
This query is running exactly one Select query to fetch the Children entities. Check the below mentioned logs.
HIBERNATE: SELECT childrens3_.id AS id1_0_,
childrens3_.date_created AS date_cre2_0_,
childrens3_.date_updated AS date_upd3_0_,
childrens3_.NAME AS name4_0_,
childrens3_.teacher_id AS teacher_5_0_ FROM city city0_
INNER JOIN school schools1_
ON city0_.id = schools1_.city_id
INNER JOIN teacher teachers2_
ON schools1_.id = teachers2_.school_id
INNER JOIN children childrens3_
ON teachers2_.id = childrens3_.teacher_id WHERE city0_.id = ?
Now what you have is an n+1 issue. To fix such issue you can use join fetch instead of simple joins.
If you want use Query annotation try this approach
#Query("Select c from Children c join fetch c.teacher t join fetch t.school s join fetch s.city ct where ct.id = :id")
I've the following DB model:
Category -< ProductCategory >- Product -< Variant
(Category has many-to-many relationship with Product and Product has one-to-many relationship with Variant)
Now I need to get all Category records that have product with active variants. I'm getting these objects via the following JPQL query:
#Query("select distinct c from Category c join c.products as p join p.variants as pv where pv.active = true")
It works well - returns categories accurately - however every single Category contains all the products - not only these with active variants.
How can I filter out the products (or variants) that are inactive in a single query?
Here's a postgres script that with database struct and sample data. For given data two categories (CAT 1, CAT 2), two products (PROD 1, PROD 2) and three variants (VAR 1, VAR 2, VAR 3) should be returned.
I had exactly the same problem and it took me a while to find out how this works. The child list should be filtered when you add FETCH after your JOIN like this:
SELECT DISTINCT c FROM Category c JOIN FETCH c.products as p join p.variants as pv where pv.active = true
I have the same problem on it, and I found that the FetchType in the #OneToMany annotation is important. It need to be set as Lazy mode. If it is Eager mode, jpa will create the sql query to fetch the data from the table for your child collection and won't filter it for you.
I have 2 entity classes Product and ProductAltID with no #OnetoMany mapping defined between them.
I want to do something like this
select p from ProductAltid inner join Product pai
where p.id = pai.id
How can I achieve this?
Add this method to the ProductAltId repository (choosing that one because the query returns ProductAltIds):
#Query("select pai from ProductAltId as pai "
+ "where pai.id in (select p.id from Product as p)")
List<ProductAltId> findForAllProducts();
I switched the aliases around, they seem backward in your example.
I keep trying variations of this query and can't seem to make this happen. I've also referenced this post: Path Expected for Join! Nhibernate Error and can't seem to apply the same logic to my query. My User object has a UserGroup collection.
I understand that the query needs to reference entities within the object, but from what I'm seeing I am...
#NamedQuery(
name = "User.findByGroupId",
query =
"SELECT u FROM UserGroup ug " +
"INNER JOIN User u WHERE ug.group_id = :groupId ORDER BY u.lastname"
)
select u from UserGroup ug inner join ug.user u
where ug.group_id = :groupId
order by u.lastname
As a named query:
#NamedQuery(
name = "User.findByGroupId",
query =
"SELECT u FROM UserGroup ug " +
"INNER JOIN ug.user u WHERE ug.group_id = :groupId ORDER BY u.lastname"
)
Use paths in the HQL statement, from one entity to the other. See the Hibernate documentation on HQL and joins for details.
You need to name the entity that holds the association to User. For example,
... INNER JOIN ug.user u ...
That's the "path" the error message is complaining about -- path from UserGroup to User entity.
Hibernate relies on declarative JOINs, for which the join condition is declared in the mapping metadata. This is why it is impossible to construct the native SQL query without having the path.
You'll be better off using where clauses. Hibernate does not accept inner joins for tables where the PK/FK relationship is not there between Entities
do
SELECT s.first_name, s.surname, sd.telephone_number FROM Student s, StudentDetails sd WHERE s.id = sd.student_id
instead of
SELECT s.first_name, s.surname, sd.telephone_number FROM Student s INNER JOIN StudentDetails sd on s.id = sd.student_id
The latter will only work if Student's id (s.id) is referenced as FK on StudentDetails (sd.student_id)) table design / erd