I have three tables with entities in hibernate. DB - MySQL. I need to get fields from entity "Item" where ModelsMm.id has some value. At first I tried to do separate queries, it was huge amount of requests in sum. So, i tried to do complex query, but it became a very long run.
I think there is a simpler way, but I do not know what.
My query and entities.
List<Item> itemIds = session.createQuery("select it from Item it where :id in elements(it.mmPrice.modelsMm)");
#Entity (name = "MODELS_MM")
public class ModelsMm {
#Id
private int Id;
#ManyToMany(cascade=CascadeType.ALL, fetch = FetchType.LAZY)
#JoinTable(name="parth_mm", joinColumns={#JoinColumn(name="MODEL_ID", referencedColumnName="ID")}, inverseJoinColumns={#JoinColumn(name="PART_ID", referencedColumnName="ID")})
private List<MmPrice> mmPrices;
#Entity (name = "MM_PRICE")
public class MmPrice {
#Id
private int id;
private String article;
#OneToOne(optional = true, fetch = FetchType.LAZY)
#JoinColumn(name = "article", referencedColumnName = "article",insertable = false, updatable = false)
private Item item;
#ManyToMany
#JoinTable(name="parth_mm", joinColumns={#JoinColumn(name="PART_ID", referencedColumnName="ID")}, inverseJoinColumns={#JoinColumn(name="MODEL_ID", referencedColumnName="ID")})
private List<ModelsMm> modelsMm;
#Entity
#Table(name="SHOP_ITEMS")
public class Item implements Serializable {
#Id
private int id;
private String article;
#OneToOne(optional = true, fetch = FetchType.LAZY)
#JoinColumn(name = "article", referencedColumnName = "article",insertable = false, updatable = false)
private MmPrice mmPrice;
In console i have that query
Hibernate: select item0_.ID as ID0_, item0_.ARTICLE as ARTICLE0_, item0_.article as article0_ from SHOP_ITEMS item0_ cross join MM_PRICE mmprice1_ where item0_.article=mmprice1_.article and (? in (select modelsmm2_.MODEL_ID from parth_mm modelsmm2_ where mmprice1_.ID=modelsmm2_.PART_ID))
Thanks.
First, you'll have to fix your mapping. In a bidirectional association, one side MUST be the inverse side, and thus use the mappedBy attribute. For example, if you choose ModelsMm to be the inverse side, then its mmPrices attribute should be declared as
#ManyToMany(mappedBy = "modelsMm")
private List<MmPrice> mmPrices;
You should also forget about CascadeType.ALL on ManyToMany associations: it makes no sense. You don't want to delete all the courses of a student when you delete a student, since the course is also followed by several other students.
Now, regarding your query, it's not very clear what you want to do. If you want to select all the items which have a price which have at least one model whose ID is in a collection of IDs, then you simply need the following query:
select distinct i from Item i
join i.mmPrice p
join p.modelsMm m
where m.id in :modelIds
Side note: please fix your naming. This inconsistent and unnecessary usage of mm as a prefix or suffix makes the code unreadable. Name your class Price, the fields of type Price price, and the collections of prices prices. Just as you would do in English: an Item has a price, and a price has models.
Related
I got following tables. Lets ignore the fact that the relation is done wrong here. I cannot change that.
Each company can have multiple employes and each employe belongs to only one company.
Table: Company
ID
EMPLOYE_ID
10
100
Table: Employe
ID
NAME
100 (Same as EMPLOYE_ID)
John
Now i want to create a relation #OneToMany between Company -> Employe . My entities look as follow
class Company {
#Id
#Column(name = "id", unique = true, nullable = false)
private String id;
#OneToMany(fetch = FetchType.LAZY)
#JoinColumn(name = "EMPLOYE_ID", referencedColumnName = "ID")
private Set<Employe> employees;
}
No matter if i try to create a uniderectional, or biderection relationship by adding also #ManyToOne on my Employe class, when using Criteria api to select all Company entities and their Employes i always end up with a wrong generated SQL query at the point where it joines the tables. The above relation for example creates following:
FROM company company0
INNER JOIN employe employe0 ON company0.id = employe0.employe_id
I tried several approaches, but i end up almost with the same error. It tries either to access a column which does not exist on the table, or joins wrong columns (e.g. id = id). Or by the following exception
Caused by: org.hibernate.MappingException: Repeated column in mapping
for entity: com.Employe column: id (should be mapped with
insert="false" update="false")"}}
What is a simple approach to create a bidrectional relation with the above table structure?
Note: I finally ended up changing the DB schema. Still, it would be interesting if someone could provide an answer for such a case, even if it is based on a not well formed
The central problem is that the described table structures do not allow a 1:n relationship from Company to Employee. According to the table design (especially the design of PKs) above, a company can only have one employee.
However, if the DB design cannot be changed, the following approach using the JoinColumnOrFormula annotation may lead to partial success.
The #JoinColumnOrFormula annotation is used to customize the join between a child Foreign Key and a parent row Primary Key when we need to take into consideration a column value as well as a #JoinFormula.
See https://docs.jboss.org/hibernate/stable/orm/userguide/html_single/Hibernate_User_Guide.html#associations-JoinColumnOrFormula for details.
More concretely with these Entities
#Entity
#Table(name="t_company")
public class Company {
#Id
#Column(name="id")
private Integer id;
#Column(name="employee_id")
private Integer employeeId;
#OneToMany(mappedBy = "company")
private List<Employee> employees;
// ..
}
#Entity
#Table(name = "t_employee")
public class Employee {
#Id
#Column(name = "id")
private Integer id;
#Column(name = "name")
private String name;
#ManyToOne
#JoinColumnOrFormula( column =
#JoinColumn(
name = "id",
referencedColumnName = "employee_id",
insertable = false,
updatable = false
)
)
private Company company;
// ..
}
and this custom repository
#Repository
public class EmployeeRepository {
#Autowired
EntityManager entityManager;
List<Employee> findAll() {
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Employee> cq = cb.createQuery(Employee.class);
Root<Employee> root = cq.from(Employee.class);
Join<Employee, Company> joinCompany = root.join("company");
TypedQuery<Employee> query = entityManager.createQuery(cq);
return query.getResultList();
}
}
you get the following query:
select
employee0_.id as id1_1_,
employee0_.name as name2_1_
from t_employee employee0_
inner join t_company company1_ on employee0_.id=company1_.employee
I have tables:
users (id, name, email, password)
user_statuses (user_id, is_premium, is_advanced, user_rank_id)
user_ranks (id, name, ordinal)
So the relation between User and UserStatus is 1-1, and I have following entity clasess:
#Entity
#Table(name = "users")
#Getter
#Setter
#NoArgsConstructor
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private long id;
private String name;
private String email;
private String password;
#OneToOne(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private UserStatus status;
}
#Entity
#Table(name = "user_statuses")
#Getter
#Setter
#NoArgsConstructor
public class UserStatus {
#Id
private long id;
#MapsId
#OneToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "user_id")
private User user;
private boolean isPremium;
private boolean isAdvanced;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "user_rank_id")
private UserRank rank;
}
#Entity
#Table(name = "user_ranks")
#Getter
#Setter
#NoArgsConstructor
public class UserRank {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private long id;
private String name;
private int ordinal;
}
Then i created endpoint "/users/{id}" which should return user's email address as a string:
#GetMapping("/users/{id}")
public String getUserEmail(#PathVariable("id") long userId) {
User user = service.getUser(userId);
return user.getEmail();
}
When I call above endpoint I get user's email address as a response, however looking at the console log I see that hibernate executed 2 queries but noone asked him to do so:
First one for fetching the user:
SELECT
user0_.id AS id1_2_0_,
user0_.email AS email2_2_0_,
user0_.name AS name3_2_0_,
user0_.password AS password4_2_0_
FROM
users user0_
WHERE
user0_.id = 1;
And second one for fetching User Status that is associated with this User object:
SELECT
userstatus0_.user_id AS user_id1_1_0_,
userstatus0_.is_advanced AS is_advan2_1_0_,
userstatus0_.is_premium AS is_premi3_1_0_,
userstatus0_.user_rank_id AS user_ran4_1_0_
FROM
user_statuses userstatus0_
WHERE
userstatus0_.user_id = 1;
So I am confused: Why is hibernate running second query when I set fetch = FetchType.LAZY on each relation... It looks like that LAZY is ignored for #OneToOne annotation?
I do not use EntityGraph.
How to stop hibernate for running second query?
EDIT
So, it turns out Hibernate ignores my Lazy hint because it needs to decide should it initialize property with NULL or ProxyObject which makes sense. This link explains it well:
https://thorben-janssen.com/hibernate-tip-lazy-loading-one-to-one/
However this link also suggests that the best way to model this is Unidirectional One to One and it says that I can always fetch UserStatus based on User's ID (because both tables "shares" primary key)
However this confuses me a little bit, because I can fetch both rows using single query (SELECT * FROM users LEFT JOIN user_statuses ON users.id = user_statuses.user_id), but with approach described in the link I need 2 queries, and as far as I know (which I might be wrong) is 1 query is better than executing 2 queries, also if I want to fetch 25 users and their User Statuses, then I would also need 2 queries, one for fetching users and then fetching corespoinding user statuses and finally write nested for each loops to join these objects. I could have just executed one single query to fetch everything...
It is possible to make OTO lazy even if it's not the owning side. You just need to mark it as optional = false. This way Hibernate will know that it can safely a create proxy (and null is not possible) as the association always exists. Note, though it really must be non-optional - the 2nd entity must always exist. Otherwise you'll get an exception once Hibernate tries to load it lazily.
As for the number of queries, with native Hibernate (not JPA!) you can select org.hibernate.annotations.FetchMode. Which gives options to:
Use a separate select
Or use a join to load association
Alternatively, you can stay with JPA and write a JPQL query and use fetch join to keep it as a single query.
PS: before doing additional select Hibernate will check if the element already exists within the Session. If it is, then no select is going to be issued. But with fetch join or FetchMode.JOIN you won't have this luxury - join will always happen.
For one to one relation in hibernate it is always loading reference object whether you keep Fetch type Lazy or Eager. So alternate solution is select only those columns which are needed, it should not contain that reference column. So in this case hibernate will not fire another query.
Query for below class will be :
#Query("select new Example(id,field1) from Example")
#Entity
#Table(name = "example")
class Example implements Serializable {
private static final long serialVersionUID = 1L;
public Example(Long id, String field1) {
this.id = id;
this.field1 = field1;
}
#Id
#Column(name = "id", nullable = false, updatable = false)
private Long id;
#OneToOne(mappedBy = "example", fetch = LAZY, cascade = ALL)
private CustomerDetails customerDetails;
#Column(name = "field1", nullable = false, updatable = false)
private String field1;
}
I am trying to fetch with one query list of objects and its associations, unfortuantely, either I cause N+1 requests to database, or get hit with exception "org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list".
Please let me walk you through my case.
Below is my Data Model:
#Table(name = "first_table")
public class FirstObject {
#Id
#Column(nullable = false, name = "first_id")
private Long id;
#Column(nullable = false, name = "first_param")
private String param1;
#ManyToOne
#JoinColumn(nullable = false, name = "second_id")
private SecondObject second;
...other columns...
}
#Table(name = "second_table")
public class SecondObject {
#Id
#Column(nullable = false, name = "second_id")
private Long id;
#Column(nullable = false, name = "second_param")
private Long param2;
#ManyToOne
#JoinColumn(nullable = false, name = "third_id")
private ThirdObject third;
...other columns...
}
#Table(name = "third_table")
public class ThirdObject {
#Id
#Column(nullable = false, name = "third_id")
private Long id;
...other columns...
}
It is true to database relations, also exactly how I want it on FE.
All I am trying to achieve is to fetch all the associations with one query, giving 2 conditions:
ConditionBuilder condition = new ConditionBuilder()
.and(FirstObject.second.param2.eq(some_number))
.and(FirstObject.param1.eq(some_string));
return from(FirstObject)
.join(FirstObject.second).fetchJoin()
.join(FirstObject.second.third).fetchJoin()
.where(condition.generate())
.fetch();
Unfortunately this code throws exception:
org.hibernate.QueryException: query specified join fetching, but the
owner of the fetched association was not present in the select list
I can make it work, but with N+1 queries, but it is acceptable only for development phase, as will cause performance issue.
...
.join(FirstObject.second).fetchJoin()
.join(FirstObject.second.third)
...
same here:
...
.join(FirstObject.second)
.join(FirstObject.second.third)
...
What I am trying to figure out is how to make hibernate to create one simple query like that:
select
*
from
first_table table1
inner join
second_table table2
on table1.second_id=table2.second_id
inner join
third_table table3
on table2.third_id=table3.third_id
where
table1.first_param="some_string"
table2.second_param=some_number
All the help is very much appreciated, I've been fighting this for some time now, and really counting on community. Thank you very much.
You should be mapping both sides of the entity relationship:
for instance, in FirstObject you have this:
#ManyToOne
#JoinColumn(nullable = false, name = "second_id")
private SecondObject second;
So in SecondObject you should have this:
#OneToMany(mappedBy = "second") // this is the name of the field in the class that defines the join relationship
Collection<FirstObject> firstObjects;
In ThirdObject you should have this:
#OneToMany(mappedBy = "third") // this is the name of the field in the class that defines the join relationship
Collection<SecondObject> secondObjects;
In my Java programm I got two entities Invoice and Category (like insurance, salary, car,...). Each Invoice belongs to exactly one Category. Now I want to display a table which lists all existing categories and the number if times they are actually used for an invoice. Like this:
The SQL would look like this:
select categories.name, categories.id, count(invoice.id) as usages
from categories
left join invoice on categories.id = invoice.category_id
group by categories.id
As I'm pretty new to Hibernate I studied the official documentation, but the documentation does only show examples based on a Person and Address relationship. However in my case Category does not have a direct linking to Invoice (it is the other way around: each invoice has a category id). So I played around with the code and came up with the following source code. Which obviously has one serious drawback as I do not get the categories without invoices:
CriteriaBuilder criteriaBuilder = session.getCriteriaBuilder();
CriteriaQuery<CategoryWrapper> criteria = criteriaBuilder.createQuery(CategoryWrapper.class);
Root<Invoice> invoiceRoot = criteria.from(Invoice.class);
Join<Invoice, Category> invoiceJoin = invoiceRoot.join(Invoice_.category);
criteria.select(
criteriaBuilder.construct(
CategoryWrapper.class,
invoiceJoin.get(Category_.id),
invoiceJoin.get(Category_.name),
criteriaBuilder.count(invoiceRoot.get(Invoice_.id))
)
);
criteria.groupBy(invoiceJoin.get(Category_.id));
return session.createQuery(criteria).getResultList();
My question is: How can I get all categories with the number of usages even if no invoice exists for a specific category?
Entities
#Entity
#Table(name = "categories")
public class Category {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private int id;
#Column(name = "name")
private String name;
[... getter and setter ]
}
#Entity
#Table(name = "invoice")
public class Invoice {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private int id;
#Column(name = "date")
private Date date;
#ManyToOne
#JoinColumn(name = "category_id")
private Category category;
#Column(name = "description")
private String description;
#Column(name = "amount")
private String amount;
#Column(name = "income", columnDefinition = "BOOLEAN")
private boolean income;
[...getter and setter...]
}
EDIT1
updated the SQL to use a left join. However using a LEFT join in the java code does not work.
Join<Invoice, Category> invoiceJoin = invoiceRoot.join(Invoice_.category, JoinType.LEFT);
I only get the categories with invoices (as shown in the image above). But in the database more categories are available:
EDIT2
As invoices is the left table and categories is the right table I tried to use RIGHT join
Join<Invoice, Category> invoiceJoin = invoiceRoot.join(Invoice_.category, JoinType.RIGHT);
but that did not work
Caused by: java.lang.UnsupportedOperationException: RIGHT JOIN not
supported
EDIT3
I checked the console output: even if I use a JoinType.LEFT (as shown in EDIT1) the programm will still use a INNER join:
select category1_.id as col_0_0_, category1_.name as col_1_0_, count(invoice0_.id) as col_2_0_ from invoice invoice0_ inner join categories category1_ on invoice0_.category_id=category1_.id group by category1_.id
But why?
I have a Person class that has a collection of Contacts. Everything works ok, I get the list of persons with their contacts. However, in log I see that a separate query is made to read collection of every person. That is too bad.
How to make hibernate make a join to read all the data in one query? I use JPA.
This is the person class:
#Entity
#Table(name = "tbl1")
public class PersonItem implements Serializable{
#Id
#Column(name="col1")
private String guid;
.....
#ElementCollection(targetClass = ContactItem.class,fetch=FetchType.EAGER)
#CollectionTable(name="tbl2",joinColumns=#JoinColumn(name="col2"))
private List<ContactItem> contacts;
....
}
This is the contact class
#Embeddable
#Table(name = "tbl2")
public class ContactItem implements Serializable {
#Column(name="col1")
private String guid;
#Column(name="col3")
private String info;
}
This is the way I get the list of persons:
Query query = em.createQuery("Select p from PersonItem p WHERE p.guid IN (:guids)");
query.setParameter("guids", guids);
List<PersonItem> list=query.getResultList();
And this what I see in log (I have three persons in DB):
Hibernate: select personitem0_.col1 as col1_0_, personitem0_.col4 as col2_0_, personitem0_.col2 as col3_0_, personitem0_.col3 as col4_0_ from tbl1 personitem0_ where personitem0_.col1 in (? , ? , ?)
Hibernate: select contacts0_.col2 as col1_1_0_, contacts0_.col1 as col2_1_0_, contacts0_.col3 as col3_1_0_ from tbl2 contacts0_ where contacts0_.col2=?
Hibernate: select contacts0_.col2 as col1_1_0_, contacts0_.col1 as col2_1_0_, contacts0_.col3 as col3_1_0_ from tbl2 contacts0_ where contacts0_.col2=?
Hibernate: select contacts0_.col2 as col1_1_0_, contacts0_.col1 as col2_1_0_, contacts0_.col3 as col3_1_0_ from tbl2 contacts0_ where contacts0_.col2=?
Please, begin from a more simple mapping. Use plural names, and column prefixes.
#Entity
#Table(name = "persons")
public class Person {
#Id
#Column(name = "f_guid")
private String guid;
#OneToMany(mappedBy = "person", fetch = FetchType.EAGER)
private List<Contact> contacts;
}
#Entity
#Table(name = "contacts")
public class Contact {
#Id
#Column(name = "f_guid")
private String guid;
#Column(name = "f_info")
private String info;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "fk_person")
private Person person;
}
Person is associated to contacts by a foreign key fk_person in the contacts table.
Update
Looks like JPQL overrides a default fetching strategy. You need to specify a fetch explicitly
select p from PersonItem p left join fetch p.contacts WHERE p.guid IN (:guids)
If you have duplicates, cause of joins, you can use distinct
select distinct p from PersonItem p left join fetch p.contacts WHERE p.guid IN (:guids)
Try #Fetch on your relation.
Also i would suggest to use #OneToMany relation int this case
#OneToMany(mappedBy = "person", fetch = FetchType.EAGER)
#Fetch(FetchMode.JOIN) //You can use SUBSELECT as well
private List<ContactItem> contacts;
You can read more about fetching strategies here
fetch-“join” = Disable the lazy loading, always load all the collections and entities.
fetch-“select” (default) = Lazy load all the collections and entities.
batch-size=”N” = Fetching up to ‘N’ collections or entities, Not record.
fetch-“subselect” = Group its collection into a sub select statement.