I set up a Database Application with Spring an Hibernate and I'm using a Many-To-Many-Relationship.
Here's the code:
Author.java
#ManyToMany(cascade = {CascadeType.ALL})
#JoinTable(name = "writes", joinColumns = {#JoinColumn(name = "authorId")}, inverseJoinColumns = {#JoinColumn(name = "publicationId")})
private Set<Publication> publications = new HashSet<Publication>();
Publication.java
#ManyToMany(mappedBy = "publications")
private Set<Author> authors = new HashSet<Author>();
these lines of code generate a connection-table named writes, but when I try to run a query over all Tables int gives me the error, named above.
this is the method, that schould run the query:
#Transactional
public List<Author> findAuthorByLastname(String lastName) {
String hql = "from Author a, Publication p, writes w where a.id = w.authorId and p.id = w.publicationId and a.lastname = :lastName";
Query q = sessionFactory.getCurrentSession().createQuery(hql);
q.setParameter("lastName", lastName);
List<Author> result = q.list();
return result;
}
You don't need to mention connection table explicitly in HQL queries (moreover, you even cannot mention them - only mapped entities). You need to use join on mapped relationships instead.
Also, it's not quite clear what you want to achieve.
If you want to fetch Authors with eagerly filled collections of their Publications in one query, use join fetch:
select distinct(a) from Author a join fetch a.publications where a.lastName = :lastName
If you want to fetch a list of pairs (Author, Publication), use regular join:
select a, p from Author a join a.publications p where a.lastName = :lastName
Related
My problem is the following,
There are two entity classes, let's call them Entity1 and Entity2 with One-to-Many relationship in between, i.e. one Entity1 contains multiple Entity2s, and Entity2 may have only one Entity1:
#Entity
#Table(name = "entity1")
public class Entity1 {
int x;
int y;
...
#LazyCollection(LazyCollectionOption.TRUE)
#OneToMany(mappedBy = "e1", cascade = CascadeType.ALL, orphanRemoval = true)
private Set<Entity2> entity2s = new HashSet<>();
}
#Entity
#Table(name = "entity2")
public class Entity2 {
int a;
int b;
...
#ManyToOne
#JoinColumn(name = "entity1_id")
#JsonBackReference
private Entity1 e1;
}
Now I would like to issue a query for retrieving Entity2s with WHERE conditions for both Entity2 and its corresponding Entity1:
#Query("SELECT " +
" e2 " +
"FROM " +
" Entity2 e2 " +
"WHERE " +
" e2.a = '<val1>' AND e2.b = '<val2>' AND e2.e1.x = '<val3>' AND e2.e1.y ='<val4>'")
List<Entity2> findMyEntity2s(
#Param...,
#Param...,
);
So the problem with this approach is that, it indeed gets desired Entity2s by cross joining entity1 and entity2 tables with specified WHERE conditions BUT it fetches e1s for each of those Entity2s in the result with a separate query.
So for example if the result of join is 5 Entity2s, there will be 5 additional queries to entity1 table.
I tried to set #ManyToOne in Entity2 as #ManyToOne(fetch = FetchType.LAZY) but it didn't help. I guess that's expected because LAZY would simply postpone the retrieval of e1s but wouldn't eliminate it completely.
Next, I read about #EntityGraph, and added it to Entity2:
#Entity
#Table(name = "entity2")
#NamedEntityGraph(name = "graph.entity2.entity1",
attributeNodes = { #NamedAttributeNode("e1") })
public class Entity2 {
int a;
int b;
...
#ManyToOne
#JoinColumn(name = "entity1_id")
#JsonBackReference
private Entity1 e1;
}
and in the repository, I added it as:
#EntityGraph(value = "graph.entity2.entity1")
#Query("SELECT " +
" e2 " +
"FROM " +
" Entity2 e2 " +
"WHERE " +
" e2.a = '<val1>' AND e2.b = '<val2>' AND e2.e1.x = '<val3>' AND e2.e1.y ='<val4>'")
List<Entity2> findMyEntity2s(
#Param...,
#Param...,
);
In this case, the separate SQL queries disappear, EntityGraph does left join and its result contains columns from both entity1 and entity2, BUT because the conditions for e2.e1 are still in WHERE clause, it adds ONE MORE unnecessary cross join with entity1 table (e2.e1 conditions are checked in that cross join).
I couldn't find a way to get rid of that extra cross join, so now I'm using the following query:
#EntityGraph(value = "graph.entity2.entity1")
#Query("SELECT " +
" e2 " +
"FROM " +
" Entity2 e2 " +
"WHERE " +
" e2.a = '<val1>' AND e2.b = '<val2>'")
List<Entity2> findMyEntity2s(
#Param...,
#Param...,
);
So basically I get Entity2s and in the application I filter out based on conditions of Entity1 (e2.e1.x = '<val3>' AND e2.e1.y ='<val4>').
Is there a way to make it work with a single join only, for both entity's conditions, not only Entity2 conditions? The way I'm doing it now, does not seem correct and efficient to me, and I feel there's a way to do that using repository method only, without involving the app. Would appreciate any help on this
UPD. Read about nativeQuery option (nativeQuery = true) for #Query annotation, which allows specifying a raw query and thus bypassing entity-based query, but the query still fetches many-to-one e1 field, using entity1_id (entity graph was disabled). I tried to enable entity graph but it dropped exception stating that entity graph cannot be used with native query, which is expected
This is the classic n + 1 query problem.
You can read the detail here: https://vladmihalcea.com/n-plus-1-query-problem/
In your query, append:
LEFT JOIN FETCH e2.e1 e2e1
This will fetch e1 with e2 in the first and single query.
Don't forget; always use FetchType.LAZY and fetch your entities with JOIN FETCH. Otherwise, you will get into a big mass while the scope of the project enlarges.
In addition, why do you use Jaxson annotations in your Entity classes? Use entities for only DAO access and map them to another DTOs to use elsewhere.
that's fragment of my Employee entity/class:
#Entity
#Table
public class Employee {
...
#ManyToOne(.....)
#JoinColumn(name="department_id")
private Department department;
}
Now, I want to fetch all Employees from specific Department (employees with specific department_id):
CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Employee> criteriaQuery = builder.createQuery(Employee.class);
Root<Employee> employeeRoot = criteriaQuery.from(Employee.class);
criteriaQuery.select(employeeRoot);
criteriaQuery.where(builder.equal(employeeRoot.get(????????????), id));
There's my problem. How do I access Department.id? I know i have to get({specific field}) but i dunno how. Should I somehow join those tables first? Looking forward for your answers!
You need create a join with your relationed table.
Ex:
CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Employee> criteriaQuery = builder.createQuery(Employee.class);
Root<Employee> employeeRoot = criteriaQuery.from(Employee.class);
Join<Employee, Departament> join = from.join("department", JoinType.INNER);
criteriaQuery.where(builder.equal(join.get("specific_fied"), your_specific_fied));
TypedQuery<Employee> typedQuery = session.createQuery(criteriaQuery);
List<Employee> employees = typedQuery.getResultList();
for (Employee e : employees) {
System.out.println(e.getName());
}
session.getTransaction().commit();
session.close();
entityManagerFactory.close();
If you want anything same as this query:
SELECT c, p.name FROM Country c LEFT OUTER JOIN c.capital p
you can build this:
CriteriaQuery<Country> q = cb.createQuery(Country.class);
Root<Country> c = q.from(Country.class);
Join<Country> p = c.join("capital", JoinType.LEFT);
q.multiselect(c, p.get("name"));
If you what build anything same as this query:
SELECT c FROM Country c JOIN FETCH c.capital
you can build this:
CriteriaQuery<Country> q = cb.createQuery(Country.class);
Root<Country> c = q.from(Country.class);
Fetch<Country,Capital> p = c.fetch("capital");
q.select(c);
For more exemples see FROM clause (JPQL / Criteria API)
I'm using Spring Boot v1.5.3
In my code, I have a search operation with a lot of conditions.
public Page<ParentObject> search(Pageable pageable) {
Specification<ParentObject> specification = (root, cq, cb) -> {
Predicate p = cb.and(
cb.equals(root.get("child").get("id"), "someValue"),
// a lot of predicates appended by conditions
);
return p;
};
Sort newSort = pageable.getSort().and(new Sort(Sort.Direction.ASC, "child.id"));
pageable = new PageRequest(pageable.getPageNumber(), pageable.getPageSize(), newSort)
Page<ParentObject> result = parentObjectRepository.findAll(specification, pageable);
return result;
}
The problem is that my parent table contains child_id field with index. And I want SQL to be like:
SELECT .... FROM parent p INNER JOIN child c ON c.id = p.child_id WHERE ...
ORDER BY p.child_id ASC;
But in result I have:
SELECT .... FROM parent p INNER JOIN child c ON c.id = p.child_id WHERE ...
ORDER BY c.id ASC;
Pay attention to ORDER BY clause. If I have c.id index is not involved and the search is slow. If I have ORDER BY p.child_id it works much faster.
I tried to use
Sort newSort = pageable.getSort().and(new Sort(Sort.Direction.ASC, "child"));
but it does not work as expected.
Entity:
public class ParentObject {
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "child_id", referencedColumnName = "id")
private ChildObject child;
}
I can't replace this by native SQL, because this search specification contains 30+ if/else statements and it will take a lot of time to rewrite the code.
How can I solve this problem? Thanks in advance for your answers.
Finally, I found a solution. As we know, ORM works with database thru entities.
All my entities have String (UUID) values as ids. So, I have added the following code into my ParentObject:
public class ParentObject {
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "child_id", referencedColumnName = "id")
private ChildObject child;
#Column(name = "child_id", insertable = false, updatable = false)
private String childId;
}
As you see, here I have added simple field that contains id of child object. It's important to mark this field as insertable = false, updatable = false and we can't change this field in the code, this is read-only field. But this allows us to sort results by parent.child_id, not by child.id. If we need to replace child object, need just call setChild(newValue).
And finally, my search method now looks like:
public Page<ParentObject> search(Pageable pageable) {
Specification<ParentObject> specification = (root, cq, cb) -> {
Predicate p = cb.and(
cb.equals(root.get("child").get("id"), "someValue"),
// a lot of predicates appended by conditions
);
return p;
};
// IMPORTANT change in next line
Sort newSort = pageable.getSort().and(new Sort(Sort.Direction.ASC, "childId"));
pageable = new PageRequest(pageable.getPageNumber(), pageable.getPageSize(), newSort)
Page<ParentObject> result = parentObjectRepository.findAll(specification, pageable);
return result;
}
And in result I have the following SQL query:
SELECT .... FROM parent p INNER JOIN child c ON c.id = p.child_id WHERE ...
ORDER BY p.child_id ASC;
Hope this would be useful for someone
I have a case statement in my Native query where I am attempting to override a field in my entity.
SELECT i.id, i.ONE_TO_ONE_ID, i.ANOTHER, CASE(WHEN condition THEN 'YES' WHEN another_condition THEN 'NO' ELSE 'MAYBE' END) as word ....
I am using this with JpaRepository as a native query, with pagination.
When I run the native query against my db directly, the result set looks as though I expect.
| id_value | MAPPED_ENTITY_ID_value | another value | word_value (YES) |
When I run the native query from my JpaRepository, everything works there, except word is always null. I cant' seem to figure out how to map the additional String word result to a field in my Entity.
Is there a way to get this to map? Or will I have to create an entire #SqlResultSetMapping() for all of my fields coupled with a native query? (hoping not)
UPDATE: 1
I was generalizing above. Here is my Query.
#Query(
name = "listPagedMapping",
value = "SELECT DISTINCT i.ID, i.INSTANCE_ID, i.REGION, i.CNAME_STACK_ID, i.INSTANCE_STATE, i.IP_ADDRESS, i.EC2_ROLE_NAME, i.INSTANCE_OWNER, i.IS_MASTER, i.EC2_MASTER_ID, i.CNAME, i.EC2_START_TIMESTAMP, i.PRIVATE_DNS, i.INSTANCE_NAME, i.AUTO_TERMINATE, i.AUTO_TERMINATE_DATE, i.TERMINATION_ZONE, i.ADMIN_GROUP_AD_LDAP_ID, i.USER_GROUP_AD_LDAP_ID, (CASE WHEN i.INSTANCE_OWNER=:username THEN 'OWNER' WHEN i.ADMIN_GROUP_AD_LDAP_ID IN (g.AD_LDAP_ID) THEN 'ADMIN' WHEN i.USER_GROUP_AD_LDAP_ID IN (g.AD_LDAP_ID) THEN 'USER' END) as PERMISSION FROM USER u, USER_ACCESS_GROUPS g, EC2_PROVISIONING i WHERE i.INSTANCE_OWNER=:username and i.INSTANCE_STATE in (:instanceStates) or u.username=:username and i.INSTANCE_STATE in (:instanceStates) and g.USER_ID=u.USER_ID and (i.ADMIN_GROUP_AD_LDAP_ID IN (g.AD_LDAP_ID) or i.USER_GROUP_AD_LDAP_ID IN (g.AD_LDAP_ID))",
countQuery = "SELECT count(*) FROM (SELECT DISTINCT i.* FROM USER u, USER_ACCESS_GROUPS g, EC2_PROVISIONING i WHERE i.INSTANCE_OWNER=:username and i.INSTANCE_STATE in (:instanceStates) or u.username=:username and i.INSTANCE_STATE in (:instanceStates) and g.USER_ID=u.USER_ID and (i.ADMIN_GROUP_AD_LDAP_ID IN (g.AD_LDAP_ID) or i.USER_GROUP_AD_LDAP_ID IN (g.AD_LDAP_ID))) as ug",
nativeQuery = true)
Page<Ec2Instance> findAllByPermissionUserAdminOrOwnerAndInstanceStateIn(
#Param("username")final String username,
#Param("instanceStates") final Set<String> instanceStates,
final Pageable pageable);
}
Obviously a bit more complex.
I can get it to map to the entity field with using a named query, but then I loose all the default mappings:
#JsonInclude(JsonInclude.Include.NON_NULL)
#SuppressWarnings("unused")
#Data
#AllArgsConstructor
#NoArgsConstructor
#EqualsAndHashCode(exclude={"masterNode", "workers", "associatedBuckets"})
#Entity
#Table(name = "EC2_PROVISIONING")
#SqlResultSetMapping(
name="listPagedMapping",
columns = {
#ColumnResult(name = "permission", type = String.class)
}
)
#NamedNativeQuery(
name = "listAccessibleInstances",
query = ACCESSIBLE_QUERY,
resultSetMapping = "listPagedMapping"
)
public class Ec2Instance {
....
private String permission;
#column(name = "INSTANCE_ID")
private String instanceId;
#ManyToOne
#JoinColumn(name = "EC2_MASTER_ID")
private Ec2Instance masterNode;
#Setter(AccessLevel.NONE)
#ManyToMany(fetch = FetchType.EAGER)
#JoinTable(name = "WORKER_EC2_NODES", joinColumns = { #JoinColumn(name = "EC2_MASTER_ID") }, inverseJoinColumns = {
#JoinColumn(name = "ID") })
private Set<Ec2Instance> workers = new HashSet<>();
... More fields ..
}
I guess, I am hoping there is a way to provide a single mapping on-top of the default mapping that is done by ORM. The above code results in only a pageable of Content PERMISSION, rather than the whole entity + permission.
UPDATE: 2
Ok, so I am getting closer... Seems by removing the #ColumnResult I do get the default mapping, plus the PERMISSION field mapped over! Looks like this:
#SqlResultSetMapping(
name="listPagedMapping"
)
The last issue is it does not accept my CountQuery, and causes my tests to fail whenever a Pagination Query results with multiple pages. Looks like Spring try's to come up with its own CountQuery, which is not correct.
UPDATE: 3
To finish this off, looks like I can provide the Count Query as described here: Spring Data - Why it's not possible to have paging with native query
I will give this a go and update back.
I never got this to work quite how I wanted. I am sure I could by mapping my entire entity, but, that would have been painstaking. I ended up solving this by using NamedNativeQueries, with mapping for the additional Column as a result of my Case statement. My entity class is now annotated like:
#JsonInclude(JsonInclude.Include.NON_NULL)
#SuppressWarnings("unused")
#Data
#AllArgsConstructor
#NoArgsConstructor
#EqualsAndHashCode(callSuper = false)
#Entity
#Table(name = "EC2_PROVISIONING")
#SqlResultSetMappings({
#SqlResultSetMapping(
name = "listPagedMapping",
entities = {
#EntityResult(
entityClass = Ec2Instance.class
)
},
columns = {#ColumnResult(name = "permission", type = String.class)}
),
#SqlResultSetMapping(name = "listPagedMapping.count", columns = #ColumnResult(name = "cnt"))
})
#NamedNativeQueries({
#NamedNativeQuery(
name = "Ec2Instance.listAccessibleInstances",
query = ACCESSIBLE_QUERY,
resultClass = Ec2Instance.class,
resultSetMapping = "listPagedMapping"
),
#NamedNativeQuery(
name = "Ec2Instance.listAccessibleInstances.count",
resultSetMapping = "listPagedMapping.count",
query = ACCESSIBLE_QUERY_COUNT
)
})
We also dont need the permission field in this entity anymore. I removed that.
Then in my Repository:
Page<Object[]> listAccessibleInstances(
#Param("username")final String username,
#Param("instanceStates") final Set<String> instanceStates,
final Pageable pageable);
Thats it! Now the result of my case statement is returned with each entity.
Object[0] = original, default mapped entity.
Object[1] = permission
Trying to wrap my head around Criteria API (ouch). I have 3 classes: Devices, Offices, and SiteCodes. all joined
Devices.java
private Offices office;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "office_id")
public Offices getOffice() {
return office;
}
public void setOffice(Offices office) {
this.office = office;
}
Offices.java:
private List<SiteCodes> siteCodes;
#ManyToMany(cascade = CascadeType.PERSIST)
#JoinTable(name = "site_code_map", joinColumns = {
#JoinColumn(name = "office_id") }, inverseJoinColumns = {
#JoinColumn(name = "site_code_id") })
#OrderBy("siteCode ASC")
public List<SiteCodes> getSiteCodes() {
return this.siteCodes;
}
public void setSiteCodes(List<SiteCodes> siteCodes) {
this.siteCodes = siteCodes;
}
SiteCodes.java
private id;
private String siteCode;
<getters and setters>
I'm trying to find Devices.devId using the site code. The sql would look like this:
SELECT d.dev_id
FROM devices d, offices o, site_code_map s, site_codes ss
WHERE d.office_id=o.office_id
AND s.office_id=o.office_id
AND s.site_code_id=ss.site_code_id
AND ss.`site_code`='0S21'
I'm trying to use joins, but don't quite get how to do it. I got the following to compile:
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Integer> cq = cb.createQuery(Integer.class);
Root<Devices> d = cq.from(Devices.class);
Join<Devices, Offices> join1 = d.join(Devices_.office);
ListJoin<Offices,SiteCodes> join2 = join1.join(Offices_.siteCodes);
I couldn't figure how to use join2 so I used join1 and a path like this
ParameterExpression<SiteCodes> p = cb.parameter(SiteCodes.class, "sitecode");
Predicate pr = cb.isMember(p, join1.get(Offices_.siteCodes));
cq.where(pr);
and eventually
TypedQuery<Integer> tq = em.createQuery(cq);
<set parameter here to a SiteCode object>
List<Integer> idList = tq.getResultList();
It produces sql like the following. That subquery doesn't belong - I want it to use a join and anyway it throws a TransientObjectException even though all I'm doing is selecting:
select
devices0_.dev_id as col_0_0_
from
devices devices0_
inner join
offices offices1_
on devices0_.office_id=offices1_.office_id
inner join
site_code_map sitecodes2_
on offices1_.office_id=sitecodes2_.office_id
inner join
site_codes sitecodes3_
on sitecodes2_.site_code_id=sitecodes3_.site_code_id
where
? in (
select
sitecodes4_.site_code_id
from
site_code_map sitecodes4_
where
offices1_.office_id=sitecodes4_.office_id
And anyway it also throws this error (not including whole stack trace unless sopmeone wants to see it):
Caused by: org.hibernate.TransientObjectException: object references an
unsaved transient instance - save the transient instance before
flushing: dne.nmst.dac.model.SiteCodes
This confused me because I wasn't doing any saving, just selecting.
How do I get this to work? I want the criteria constructed properly and of course to not have an error occur.
I got this worked out. Hope it helps someone else. Still don't know why I got the error it did, but I figured out the join's and that made the query work correctly
Joins:
Root<Devices> d = cq.from(Devices.class);
Join<Devices, Offices> join1 = d.join(Devices_.office);
ListJoin<Offices,SiteCodes> join2 = join1.join(Offices_.siteCodes);
Parameter expression and Predicate:
ParameterExpression<String> p = cb.parameter(String.class, "sitecode");
Predicate pr = cb.equal(join2.get(SiteCodes_.siteCode),p);
Produced SQL like this:
select
devices0_.dev_i a col_0_0
from
devices devices0
inner join
office offices1
o devices0_.office_id=offices1_.office_i
inner join
site_code_map sitecodes2
o offices1_.office_id=sitecodes2_.office_i
inner join
site_code sitecodes3
o sitecodes2_.site_code_id=sitecodes3_.site_code_i
where
sitecodes3_.site_code=?