We decided to use hibernate inheritance mapping strategy with discriminator ( see 10.1.3 : https://docs.jboss.org/hibernate/orm/5.0/manual/en-US/html/ch10.html#inheritance-tablepersubclass-discriminator ) for loading of relatively small amount of read-only data ( ~ 20 000 rows in single table, 80 entity types, each row contains in average 100 characters).
When application starts hibernate loads these entities via ~80 queries + another ~150 queries is made to establish relationships between them. This is of course time consuming and unnecessary.
I would not mind to load whole table by single query, but how to get entity type mapping right as we use discriminator column ?
Of course there is always option to load & map it manually but we would like to stick with hibernate.
hibernate configuration of abstract entity :
#Entity
#DiscriminatorColumn(name = "DISCRIMINATOR_COLUMN", discriminatorType = DiscriminatorType.STRING, length = 30)
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
#Table(name = "MAIN_TABLE")
public abstract class ApplicationAbstractEntity
...
subclass configuration example :
#Entity
public class SomeSubEntity extends ApplicationAbstractEntity
...
Load entities for given subclass (this repeats for each subclass, 80 entity types = 80 queries) :
currentHibernateSession.createCriteria(SomeSubEntity.class);
Use setResultTransformer with your custom transformer to map result to your entities.
You can load all your entities with one query like
currentHibernateSession.createCriteria(ApplicationAbstractEntity.class).setResultTransformer(new CustomResultTransformer());
Related
I have a Room database where I want to run a basic UPDATE Table SET Column = ? WHERE Column2 = ?.
I can execute my query like so
val db = ... /// my room database
val sqlDb = db.openHelper.writableDatabase
sqlDb.execSQL(query.toString(), arrayOf(valueFor1, valueFor2))
However this didn't sit so great with me as I am not clear on whether I am meant to close the sqlDb after each query or I can leave it and let Room re-use it, as well as this feels like dropping down to lower-level API.
I tried using Room's own query method like so:
db
.query(SimpleSQLiteQuery(query.toString(), arrayOf(valueFor1, valueFor2)))
.close()
However, no update happens to the data in my db.
Is there any way for me to execute this query from RoomDatabase object directly?
Note: I do NOT want to use DAO at all. My query is dynamically created by inspecting columns in the db and I have about 100 tables in my database, I don't want to have to add this to every DAO.
In an #Dao annotated interface have a function:-
#Query("UPDATE Table SET Column=:newValue WHERE Column2=existingValue")
fun myUpdate(existingValue: String, newValue: String)
In the #Database annotated class you define an abstract function to get the #Dao annotated class. Which allows you to then get the Dao interface/abstract class and use the functions.
Then you would use something like:-
val db = ... /// my room database
val dao = getTheDao()
dao.myUpdate("OLD","NEW")
I am creating entity for table created outside of my system. I want to bind data from other table to entity field by using #SecondaryTable (or possibly better solution), but only to do so if condition is met. IE. my table has 1 row, I want to bind data from other table (oneToMany) where certain condition is met (exactly one match from other table(transform to one to one)). Can I use #Where annotation and how? If not is there alternative?
Edit: here is the entity and additional info on the related table
#Entity
#Table(name = "RE_STORAGE_INSTANCE")
public class Movie {
#Id
#Column(name="ID_")
private Long id;
...
//Column I want to fetch
private Date dueDate;
}
Table RE_VARIABLES manyToOne to table RE_STORAGE_INSTANCE, contains fields: re_key, re_value. I want to fetch re_value only if 're_key' equals dueDate. Even though it's manyToOne, only one row of RE_VARIABLES contains due date for each RE_STORAGE_INSTANCE row.
I have a domain object in Spring which I am saving using JpaRepository.save method and using Sequence generator from Postgres to generate id automatically.
#SequenceGenerator(initialValue = 1, name = "device_metric_gen", sequenceName = "device_metric_seq")
public class DeviceMetric extends BaseTimeModel {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "device_metric_gen")
#Column(nullable = false, updatable = false)
private Long id;
///// extra fields
My use-case requires to do an upsert instead of normal save operation (which I am aware will update if the id is present). I want to update an existing row if a combination of three columns (assume a composite unique) is present or else create a new row.
This is something similar to this:
INSERT INTO customers (name, email)
VALUES
(
'Microsoft',
'hotline#microsoft.com'
)
ON CONFLICT (name)
DO
UPDATE
SET email = EXCLUDED.email || ';' || customers.email;
One way of achieving the same in Spring-data that I can think of is:
Write a custom save operation in the service layer that
Does a get for the three-column and if a row is present
Set the same id in current object and do a repository.save
If no row present, do a normal repository.save
Problem with the above approach is that every insert now does a select and then save which makes two database calls whereas the same can be achieved by postgres insert on conflict feature with just one db call.
Any pointers on how to implement this in Spring Data?
One way is to write a native query insert into values (all fields here). The object in question has around 25 fields so I am looking for an another better way to achieve the same.
As #JBNizet mentioned, you answered your own question by suggesting reading for the data and then updating if found and inserting otherwise. Here's how you could do it using spring data and Optional.
Define a findByField1AndField2AndField3 method on your DeviceMetricRepository.
public interface DeviceMetricRepository extends JpaRepository<DeviceMetric, UUID> {
Optional<DeviceMetric> findByField1AndField2AndField3(String field1, String field2, String field3);
}
Use the repository in a service method.
#RequiredArgsConstructor
public class DeviceMetricService {
private final DeviceMetricRepository repo;
DeviceMetric save(String email, String phoneNumber) {
DeviceMetric deviceMetric = repo.findByField1AndField2AndField3("field1", "field", "field3")
.orElse(new DeviceMetric()); // create new object in a way that makes sense for you
deviceMetric.setEmail(email);
deviceMetric.setPhoneNumber(phoneNumber);
return repo.save(deviceMetric);
}
}
A word of advice on observability:
You mentioned that this is a high throughput use case in your system. Regardless of the approach taken, consider instrumenting timers around this save. This way you can measure the initial performance against any tunings you make in an objective way. Look at this an experiment and be prepared to pivot to other solutions as needed. If you are always reading these three columns together, ensure they are indexed. With these things in place, you may find that reading to determine update/insert is acceptable.
I would recommend using a named query to fetch a row based on your candidate keys. If a row is present, update it, otherwise create a new row. Both of these operations can be done using the save method.
#NamedQuery(name="getCustomerByNameAndEmail", query="select a from Customers a where a.name = :name and a.email = :email");
You can also use the #UniqueColumns() annotation on the entity to make sure that these columns always maintain uniqueness when grouped together.
Optional<Customers> customer = customerRepo.getCustomersByNameAndEmail(name, email);
Implement the above method in your repository. All it will do it call the query and pass the name and email as parameters. Make sure to return an Optional.empty() if there is no row present.
Customers c;
if (customer.isPresent()) {
c = customer.get();
c.setEmail("newemail#gmail.com");
c.setPhone("9420420420");
customerRepo.save(c);
} else {
c = new Customer(0, "name", "email", "5451515478");
customerRepo.save(c);
}
Pass the ID as 0 and JPA will insert a new row with the ID generated according to the sequence generator.
Although I never recommend using a number as an ID, if possible use a randomly generated UUID for the primary key, it will qurantee uniqueness and avoid any unexpected behaviour that may come with sequence generators.
With spring JPA it's pretty simple to implement this with clean java code.
Using Spring Data JPA's method T getOne(ID id), you're not querying the DB itself but you are using a reference to the DB object (proxy). Therefore when updating/saving the entity you are performing a one time operation.
To be able to modify the object Spring provides the #Transactional annotation which is a method level annotation that declares that the method starts a transaction and closes it only when the method itself ends its runtime.
You'd have to:
Start a jpa transaction
get the Db reference through getOne
modify the DB reference
save it on the database
close the transaction
Not having much visibility of your actual code I'm gonna abstract it as much as possible:
#Transactional
public void saveOrUpdate(DeviceMetric metric) {
DeviceMetric deviceMetric = metricRepository.getOne(metric.getId());
//modify it
deviceMetric.setName("Hello World!");
metricRepository.save(metric);
}
The tricky part is to not think the getOne as a SELECT from the DB. The database never gets called until the 'save' method.
I have entity like:
#Id
#Column_name = "abc"
int pk;
#Column_name = "def"
int id;
And I have Repository as:
interface fetchDataRepository extends jpaRepository<className, int> {
#Query("Select S_Test.nextVal from dual");
Long generateId();
}
In above example S_Test is hardcoded sequence name.
But the problem is that I want to pass sequence name dynamically as follows:
Long generateId(#Param("sequenceName") String sequenceName)
and use inside #Query annotation as:
#Query("Select :sequenceName.nextVal from dual");
Is there anyway to do that? Any suggestion would be appreciated.
Edit: Isn't there possible to use #(#entityName). If yes, then please tell me how?
Unfortunately you can only substitute in things that you could do in JDBC anyway (so, pretty much just values in the INSERT and WHERE clauses). No dynamic table, column, schema names are supported.
There is one exception that may apply, and that is a limited subset of SpEL can be used. There is one variable available - #entityName. So, assuming that the #Entity annotation on your entity class is named identically to the sequence, you could use an #Query like so:
#Query("Select #{#entityName}.nextVal from dual");
Otherwise, since your query is simple and does not involve any object relational mapping, you would probably need to Create a custom repository implementation and inject a JdbcTemplate into it in order to run the query.
Else you could inject an EntityManager and try using the JPA Criteria API - but again you arent actualy trying to map a resultset to an entity so JdbcTemplate will be simpler.
I am trying to get a sum with a one to many relationship, illustrated by the following relationship (only parent shown):
#Entity
#Table(name = "Parent")
public class Parent implements Serializable {
private static final long serialVersionUID = -7348332185233715983L;
#Id
#Basic(optional = false)
#Column(name = "PARENT_ID")
private Long parentId;
#OneToMany
#JoinColumn(name="CHILDREN", referencedColumnName="PARENT_ID")
private List<Child> children;
#Formula("(select sum(select height from children))")
private BicDecimal totalHeight
}
It is pretty straight forward with no restrictions and even with static restrictions. I am having trouble when the children list is restricted dynamically though.
In my case, I am using spring data and jpa. I am using specifications to restrict the children and am getting the appropriate list of children, but obviously the sum is still for unrestricted children because there is no where clause in the #Formula tag.
I do not want to iterate over the list in java for performance reasons and because the results are paginated. Also, the sum is not of the paginated results, but of all results.
I am new to Spring Data/JPA. Historically, I could build this query dynamically or use hibernate criteria. I am OK running a completley separate query to make this calculation. it is not required that I use the #Formula annotation as there is only 1 aggregation per call. In a hibernate framework, I could just state the select clause as "sum(field)" and build the criteria. In the Spring Data/JPA framework, I can build the specifications fine which covers the criteria, but I have no idea how to manipulate the select part of the query since it seems tied so tightly to the entity.
Using the #Query annotation on the repository works as its own query if I know which fields I need to restrict on, but often the fields are null and need to be ignored for the query. There are 8 possible fields, leaving me with 256 possible combinations (2^8). That is too many methods for this in the repository.
Any ideas outside of switching frameworks?
Posting an answer to this old question since I had a somewhat similar problem recently.
I decided to go with a custom repository with a method that does the aggregation based on any Specification passed into it. Specifications can be combined to compose dynamic criteria (see org.springframework.data.jpa.domain.Specifications)
So my repository to above Child height problem would look like below:
package something
import org.springframework.data.jpa.domain.Specification;
import org.springframework.stereotype.Repository;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Root;
#Repository
public class ChildHeightRepository {
#PersistenceContext
EntityManager entityManager;
public Long getTotalHeight(Specification<Child> spec) {
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery query = cb.createQuery(Long.class);
Root root = query.from(Child.class);
return ((Long) entityManager.createQuery(
query.where(spec.toPredicate(root, query, cb))
.select(cb.sum(root.get("height")))).getSingleResult());
}
}
Have you tried in JPQL
select sum(d.height) from Parent a join a.children d
If you dont want to ignore nulls
select sum(d.height) from Parent a left join a.children d
I think other question you have is how to filter depending on the properties . I mean if you need to have a where statement with several combinations.
Why you don't try to use a List and adding to the list all the predicates you want to apply depending on the combinations you want to have. Example
Create query
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery cq = cb.createQuery(Double.class);
Root<Parent> root = cq.from(Parent.class)
Join<Parent, Child> join = cq.join(("children"));
cq.select(cb.<Double>sum(join.get("height")));
Create the list of predicates
List<Predicates> listOfpredicates = new ArrayList<Predicates>();
if(property1 != null && !"".equals(property1){
PatameterExpression<String> p = cb.parameter(String.class, "valueOfproperty1")
listOfpredicates.add(cb.equal(join.get("property1"),p);
}
Then add to the CriteriaQuery
if(listOfPredicates.size() == 1)
cq.where(listOfPredicates.get(0))
else
cq.where(cb.and(listOfPredicates.toArray(new Predicate[0])));
Finally execute the query.
TypedQuery<Double> q = em.createQuery(cq);
q.getResultList();
This will create dynamically your query with any combination.
6 years late but it still took me a while to get it to work, here is how I would do it for your mapping:
#Formula("(select sum(children.height) from children_table children inner join Parent p on children.parent_id=p.id where children.parent_id=parent_id)")
private BicDecimal totalHeight
Stuff you need to take care of:
add () to the beginning and end of your formula otherwise the syntax of the sql wont be translated correctly.
the formula query is a native SQL query to my understanding and not a JPQL some one might want to correct me on this?.
properties are those of the tables and not what you name your properties in Java so the column names and table names have to actually be the table names.