I have an entity with a lot of attributes, relationships inside. In a few cases I just need 2 simple attributes, not the rest. I tried using entity graphs, but I always get the complete entries, with all attributs, relationships...
The entity graph in my EECase-entity:
#NamedQueries({
#NamedQuery(name = EECase.QUERY_ALLCASES, query = "SELECT DISTINCT c FROM EECase c")
})
#NamedEntityGraph(name = "Case.forDropdown", attributeNodes = {
#NamedAttributeNode("caseNumber"),
#NamedAttributeNode("firstNames"),
#NamedAttributeNode("lastName")
})
In my bean I try to get the filtered cases with:
public List<EECase> getCasesForDropdown() {
TypedQuery<EECase> query = getManager().createNamedQuery(EECase.QUERY_ALLCASES, EECase.class);
EntityGraph<EECase> graph = (EntityGraph<EECase>) getManager().getEntityGraph("Case.forDropdown");
query.setHint("javax.persistence.fetchgraph", graph);
List<EECase> queryEntity = (List<EECase>) query.getResultList();
return queryEntity;
}
It seems the setHint is getting ignored?
Even if you define a hint, its still an optional thing.
I would suggest a small alternative in the form of a result class in the select being a projection (advised option if you do not plan to update the entity afterwards):
#NamedQueries({
#NamedQuery(name = EECase.QUERY_ALLCASES
, query = "SELECT new com.domain.EECase(c.caseNumber, c.firstName, c.lastName)
FROM EECase c")
})
Keep in mind to place a proper constructor to accept the columns of the projection in a given order.
You can also use a separate POJO to map the results of that query. Not necessarily the entity class itself.
Also keep in mind that you wont be able to select entire dependent entity.. only plain attributes (i assumed that is the case).
Related
I'm using a legacy database. In my example, we retrieve a product which have some characteristics. In the db, we can find a product table, a characteristic table and a jointable for the manyToMany association.
The only field i need is the label of the characteristics. So, my Product entity will contains a list of characteristics as String. I would like to not create to many entities in order to not overload my sourcecode. Let's see the example :
#Entity
#Table(name = "product")
public class Product implements Serializable {
#Id
#Column(name = "id")
private Long id;
// all field of Product entity
#ElementCollection(targetClass = String.class)
#Formula(value = "(SELECT characteristic.label FROM a jointable JOIN b characteristic ON jointable.characteristic_id = characteristic.id WHERE jointable.product_id = id)")
private Set<String> characteristics = new HashSet<>();
// Getter / setter
}
To represent my characteristics, i tried to use the association of #Formula and #ElementCollection. As you can see, the names of tables (a and b in the query) does not match with my representation of these datas.
But, when I try to load a product, I get an error like "PRODUCT_CHARACTERISTICS table not found".
Here the generated SQL query executed by hibernate :
SELECT product0_.id AS id1_14_0_,
-- Other fields
characteri10_.product_id AS product_1_15_1__,
(SELECT characteristic.label
FROM a jointable JOIN b characteristic ON jointable.characteristic_id = characteristic.id
WHERE jointable.product_id = id) AS formula6_1__,
FROM product product0_
-- Other Joins
LEFT OUTER JOIN product_characteristics characteri10_ ON product0_.cdprd = characteri10_.product_cdprd
WHERE product0_.id = ?;
In the FROM part, we can refind the call of product_characteristics table (which not exist in the database).
So, my main question is the following : How can I get the list of characterics as entity attribute ? Can I reach this result with #Formula ?
Edit
In other words, i would like to load only one attribute from Many to Many mapping. I found an example here but it works only with the id (which can find in the jointable)
I assume that what you want to achieve here is reducing the amount of data that is fetched for a use case. You can leave your many-to-many mapping as it is, since you will need DTOs for this and I think this is a perfect use case for Blaze-Persistence Entity Views.
I created the library to allow easy mapping between JPA models and custom interface or abstract class defined models, something like Spring Data Projections on steroids. The idea is that you define your target structure(domain model) the way you like and map attributes(getters) via JPQL expressions to the entity model.
A DTO model for your use case could look like the following with Blaze-Persistence Entity-Views:
#EntityView(Product.class)
public interface ProductDto {
#IdMapping
Long getId();
String getName();
#Mapping("characteristics.label")
Set<String> getCharacteristicLabels();
}
Querying is a matter of applying the entity view to a query, the simplest being just a query by id.
ProductDto a = entityViewManager.find(entityManager, ProductDto.class, id);
The Spring Data integration allows you to use it almost like Spring Data Projections: https://persistence.blazebit.com/documentation/entity-view/manual/en_US/index.html#spring-data-features
Page<ProductDto> findAll(Pageable pageable);
The best part is, it will only fetch the state that is actually necessary!
Given the following domain model, I want to load all Answers including their Values and their respective sub-children and put it in an AnswerDTO to then convert to JSON. I have a working solution but it suffers from the N+1 problem that I want to get rid of by using an ad-hoc #EntityGraph. All associations are configured LAZY.
#Query("SELECT a FROM Answer a")
#EntityGraph(attributePaths = {"value"})
public List<Answer> findAll();
Using an ad-hoc #EntityGraph on the Repository method I can ensure that the values are pre-fetched to prevent N+1 on the Answer->Value association. While my result is fine there is another N+1 problem, because of lazy loading the selected association of the MCValues.
Using this
#EntityGraph(attributePaths = {"value.selected"})
fails, because the selected field is of course only part of some of the Value entities:
Unable to locate Attribute with the the given name [selected] on this ManagedType [x.model.Value];
How can I tell JPA only try fetching the selected association in case the value is a MCValue? I need something like optionalAttributePaths.
You can only use an EntityGraph if the association attribute is part of the superclass and by that also part of all subclasses. Otherwise, the EntityGraph will always fail with the Exception that you currently get.
The best way to avoid your N+1 select issue is to split your query into 2 queries:
The 1st query fetches the MCValue entities using an EntityGraph to fetch the association mapped by the selected attribute. After that query, these entities are then stored in Hibernate's 1st level cache / the persistence context. Hibernate will use them when it processes the result of the 2nd query.
#Query("SELECT m FROM MCValue m") // add WHERE clause as needed ...
#EntityGraph(attributePaths = {"selected"})
public List<MCValue> findAll();
The 2nd query then fetches the Answer entity and uses an EntityGraph to also fetch the associated Value entities. For each Value entity, Hibernate will instantiate the specific subclass and check if the 1st level cache already contains an object for that class and primary key combination. If that's the case, Hibernate uses the object from the 1st level cache instead of the data returned by the query.
#Query("SELECT a FROM Answer a")
#EntityGraph(attributePaths = {"value"})
public List<Answer> findAll();
Because we already fetched all MCValue entities with the associated selected entities, we now get Answer entities with an initialized value association. And if the association contains an MCValue entity, its selected association will also be initialized.
I don't know what Spring-Data is doing there, but to do that, you usually have to use the TREAT operator to be able to access the sub-association but the implementation for that Operator is quite buggy.
Hibernate supports implicit subtype property access which is what you would need here, but apparently Spring-Data can't handle this properly. I can recommend that you take a look at Blaze-Persistence Entity-Views, a library that works on top of JPA which allows you map arbitrary structures against your entity model. You can map your DTO model in a type safe way, also the inheritance structure. Entity views for your use case could look like this
#EntityView(Answer.class)
interface AnswerDTO {
#IdMapping
Long getId();
ValueDTO getValue();
}
#EntityView(Value.class)
#EntityViewInheritance
interface ValueDTO {
#IdMapping
Long getId();
}
#EntityView(TextValue.class)
interface TextValueDTO extends ValueDTO {
String getText();
}
#EntityView(RatingValue.class)
interface RatingValueDTO extends ValueDTO {
int getRating();
}
#EntityView(MCValue.class)
interface TextValueDTO extends ValueDTO {
#Mapping("selected.id")
Set<Long> getOption();
}
With the spring data integration provided by Blaze-Persistence you can define a repository like this and directly use the result
#Transactional(readOnly = true)
interface AnswerRepository extends Repository<Answer, Long> {
List<AnswerDTO> findAll();
}
It will generate a HQL query that selects just what you mapped in the AnswerDTO which is something like the following.
SELECT
a.id,
v.id,
TYPE(v),
CASE WHEN TYPE(v) = TextValue THEN v.text END,
CASE WHEN TYPE(v) = RatingValue THEN v.rating END,
CASE WHEN TYPE(v) = MCValue THEN s.id END
FROM Answer a
LEFT JOIN a.value v
LEFT JOIN v.selected s
My latest project used GraphQL (a first for me) and we had a big issue with N+1 queries and trying to optimize the queries to only join for tables when they are required. I have found Cosium
/
spring-data-jpa-entity-graph irreplaceable. It extends JpaRepository and adds methods to pass in an entity graph to the query. You can then build dynamic entity graphs at runtime to add in left joins for only the data you need.
Our data flow looks something like this:
Receive GraphQL request
Parse GraphQL request and convert to list of entity graph nodes in the query
Create entity graph from the discovered nodes and pass into the repository for execution
To solve the problem of not including invalid nodes into the entity graph (for example __typename from graphql), I created a utility class which handles the entity graph generation. The calling class passes in the class name it is generating the graph for, which then validates each node in the graph against the metamodel maintained by the ORM. If the node is not in the model, it removes it from the list of graph nodes. (This check needs to be recursive and check each child as well)
Before finding this I had tried projections and every other alternative recommended in the Spring JPA / Hibernate docs, but nothing seemed to solve the problem elegantly or at least with a ton of extra code
Edited after your comment:
My apologize, I haven't undersood you issue in the first round, your issue occurs on startup of spring-data, not only when you try to call the findAll().
So, you can now navigate the full example can be pull from my github:
https://github.com/bdzzaid/stackoverflow-java/blob/master/jpa-hibernate/
You can easlily reproduce and fix your issue inside this project.
Effectivly, Spring data and hibernate are not capable to determinate the "selected" graph by default and you need to specify the way to collect the selected option.
So first, you have to declare the NamedEntityGraphs of the class Answer
As you can see, there is two NamedEntityGraph for the attribute value of the class Answer
The first for all Value without specific relationship to load
The second for the specific Multichoice value. If you remove this one, you reproduce the exception.
Second, you need to be in a transactional context answerRepository.findAll() if you want to fetch data in type LAZY
#Entity
#Table(name = "answer")
#NamedEntityGraphs({
#NamedEntityGraph(
name = "graph.Answer",
attributeNodes = #NamedAttributeNode(value = "value")
),
#NamedEntityGraph(
name = "graph.AnswerMultichoice",
attributeNodes = #NamedAttributeNode(value = "value"),
subgraphs = {
#NamedSubgraph(
name = "graph.AnswerMultichoice.selected",
attributeNodes = {
#NamedAttributeNode("selected")
}
)
}
)
}
)
public class Answer
{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(updatable = false, nullable = false)
private int id;
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "value_id", referencedColumnName = "id")
private Value value;
// ..
}
I am currently using hibernate 5.0.7 and due to limitations in HQL queries (mainly the lack of a TOP or LIMIT ability) I have come to the point where I am trying to implement a native SQL query.
Due to the way that our repositories are wired up as spring beans from interfaces we are currently using a combination of annotated queries and functional queries to obtain data.
A sample of my query is as follows
#Query(value = "SELECT * FROM some_table where (id = ?1)", nativeQuery = true)
Stream<MyObject> getMyObjectByIds(String userId);
however; my real query is more complex and makes use of GroupBy (something functional queries don't seem to have) and Top (something that direct HQL queries don't seem to have)
All of the tables and items in our database are mapped entities, and all of the data that is currently in the database has been put there by these hibernate entities to begin with. Now, when I run my query I actually get a result back that looks very much like it should be my data I end up getting back
{2, 3, 5, Whatever, null}
and in my data base I have the exact some row values
{2, 3, 5, Whatever, NULL}
however, when I try to access the stream object that I have my function type set as from my native query I end up with the error
org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.Object[]] to type [com.myorg.models.MyObject] for value '{2, 3, 5, Whatever, null}'; nested exception is org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [java.lang.Integer] to type [com.myorg.models.MyObject]
Now from what I've looked up people seem to suggest that there is an SqlResultSetMapping mapping that isn't in place somewhere, and if I look on my entity there is indeed no such mapping
#Entity
#NamedEntityGraph(
name = "MyObject.withChildren",
attributeNodes = #NamedAttributeNode(value = "objectChildren")
)
#Getter
#Setter
#Table(name = "object_table", schema = "my_table")
public class MyObject implements Serializable {
I actually even looked some stuff up and tried to implement a mapping
#SqlResultSetMapping(
name = "ObjectMapping",
entities = {
#EntityResult(
entityClass = MyObject.class,
fields = {
#FieldResult(name = "id", column = "id"),
#FieldResult(name = "childId", column = "child_id"),
#FieldResult(name = "someNumber", column = "some_numbur"),
#FieldResult(name = "someString", column = "some_string"),
#FieldResult(name = "someNullableType", column = "null_type_column")
}
)
}
)
and stuck on my entity class, but I really don't even know how/why/if this is necessary, and worse it didn't even work. Granted that this is a rather obfuscated description of my code/problem is there something simple I'm missing, or does anyone know what I may be doing wrong?
I am thankful for any and all help people are willing to provide!
In the end I've managed to get this working by attaching a #NamedNativeQuery to my entity object itself
#NamedNativeQuery(
name = "MyEntity.complexSqlQuery",
query = "SELECT TOP 10 * FROM my_table WHERE (my_table.id = ?1)",
resultClass = MyEntity.class
and then adding
#Query(nativeQuery = true)
List<MyEntity> complexSqlQuery(String whatever);
to my interface style repository. I don't know if this is ideal as it seems like dumping a crap load of queries onto the entity itself isn't exactly best practice, and I was really hoping for some annotated tag I could just throw on the query already existing in my repository (it seems like the resultClass is exactly what the #Query annotation needs to support this in my case), but it seems no such option exists.
None the less, I did get this solved, just not necessarily in the way I liked.
If anyone has some insight into what I may have missed, I would be very open to hear it, otherwise this is the solution I have come up with until then.
I would like to query audit entity in my JPA environment.
At first I do AuditQuery and it works well, but now I need more advance query witch I can't do with AuditQuery.
Now I need something like
this.em.createQuery("FROM ENTITY_AUD").getResultList();
but I get error :
QuerySyntaxException: ENTITY_AUD is not mapped [ENTITY_AUD]
I understand that this is due that I don't have entity with all properties, but I don't want to have entity because it is audit entity.
Is there a way around it? For me it would be ok to get List of Object.
You can always create native SQL query in JPA. Replace createQuery with createNativeQuery in your code:
List<Object[]> list =
this.em.createNativeQuery("SELECT * FROM ENTITY_AUD").getResultList();
Add a NamedQuery in your Audit class
#Entity
#Table(name = "ENTITY_AUD")
#NamedQueries({
#NamedQuery(name = "Audit.findAll", query = "SELECT a FROM Audit a")})
public class Audit implements Serializable {
...
}
then use the named query
List<Audit> auditList = entityManager.createNamedQuery("Audit.findAll").getResultList();
Read : Implementing a JPA Named Query
I have just recently decided to redesign my database and I used annotated objects instead of hbm files. The problem is that now I am unable to build a configuration in order to check my queries. Any ideas?
edit: By hibernate perspective I mean the Hibernate Console Perspective you can find in 3.9.1 of the following link:
http://docs.jboss.org/tools/2.1.0.Beta1/hibernatetools/html/plugins.html
You can define named queries like this
#Entity
#Table(name = "yourTable")
#NamedNativeQueries(value = {
#NamedNativeQuery(name="nativeSelectName",
query = "select blah blah blah", resultClass = YourEntityClass.class)
})
#NamedQueries(value = {
#NamedQuery(name = "hqlQuery",
query = "from YourEntityClass where ...")