what is the easiest way to map POJO to/from PostgreSQL user-defined types?
Wait until Hibernate 6.2 is released. This will happen soon (within 2022) and will come with support for mapping embeddables as structs. Also see https://hibernate.atlassian.net/browse/HHH-15327
Related
In our project we are using kotlin with JPA. All of our entities are immutable so, it is not possible to set fields of our entities directly. You have to create a new instance by using the copy method. If you want these changes to be reflected to database, you must persist this newly created entity with an explicit function call.
In the beginning, this approach looks perfect to us. However, nowadays we are having some problems like some of our instances are changing unexpectedly in the memory.
val instance1 = repository.findById(entityId)
repository.save(instance1.copy(deletedAt = Instant.now()))
..
..
assertNull(instance1.deletedAt())
In the code snipped above, instance1 is retrieved from database and its deletedAt field is set with copy method and the new instance which is created with this copy method is passed to save method of the repository. We don't set any field of instance1, we create a new instance to do these changes. However, the result on assert line is unexpectedly not-null.
It seems, There is a confliction on JPA persistence context (first level cache) and kotlin's immutable and copy method logic.
Is anyone facing this problem or any suggestion or best practices when using JPA and immutable Kotlin entities?
I suspect the problem is that you're ignoring the return value from save(). Its docs say:
Saves a given entity. Use the returned instance for further operations as the save operation might have changed the entity instance completely.
But you're not doing that; you're instead continuing to use the original instance which (as that says) may have changed.
Instead, store the return value from save(), and use that thereafter. (Either by making instance1 a var, or creating a new val and not referring to instance1 afterward.)
(This isn't a Kotlin-specific problem, and is exactly the same in Java. JPA , Spring, &c work their magic by futzing with the bytecode, so can do things your code can't — such as changing immutable values. Most of the time you can ignore it, but this case makes it obvious.)
Immutable types are not compatible on how JPA works.
JPA works around the concept of UnitOfWork, which mean objects retrieved from the database lives in a PersistedContext (1st level cache) and they get discarded once the EntityManager is closed (on a web application at the end of the HTTP request).
When using the copy method in an entity you just retrieved from the database, the copied object is considered detached from the current session meaning that changes on it cannot be tracked by JPA and the underlying implememtation (Hibernate / EclipseLink) have hard time figuring out which SQL statement needs to be fired (Insert/Update/Delete ????)
Things got way more complex when you have complex object graph with OneToMany associations and cascading options.
So my recommendation is unfortunately is to avoid Immutable types when using JPA.
I'm building a PHP application and I'm using Doctrine 2.5 to map my objects into the database. My database choice is PostgreSQL 10.
Instead of using the default schema (public), I've tagged all my classes with #ORM\Table(schema="my-schema") so it uses this schema instead of the default one. This works as intended: all the tables are created on that schema.
But I've found that tables for ManyToMany relations are not being created in my schema; instead they're created on the default one
(I suppose this is occurring because they're not backed up with a class on my model).
Then my question is if it's possible to configure somewhere the default schema I want Doctrine to use (this would also allow me to get rid of all the #ORM\Table(schema="my-schema") annotations). Maybe that is a bug on Doctrine, I don't know. Any kind of workaround to prevent this also would be appreciated.
Is there a straightforward way to generate rdbms ddl, for a set of scala classes?
I.e. to derive a table ddl for each class (whereby each case class field would translate to field of the table, with a corresponding rdbms type).
Or, to directly create the database objects in the rdbms.
I have found some documentation about Ebean being embedded in Play framework, but was not sure what side-effects may enabling Ebean in play have, and how much taming would Ebean require to avoid any of them. I have never even used Ebean before...
I would actually rather use something outside of Play, but if it's simple to accomplish in Play I would dearly like to know a clean way. Thanks in advance!
Is there a straightforward way to generate rdbms ddl, for a set of
scala classes?
Yes
Ebean
Ebean a default orm provided by play you just have to create entity and enable evolution(which is set to enable as default).It will create a (dot)sql file in conf/evolution/default directory and when you hit localhost:9000 it will show you apply script .But your tag say you are using scala so you can't really use EBean with Scala .If you do that you will have to
sacrifice the immutability of your Scala class, and to use the Java
collections API instead of the Scala one.
Using Scala this way will just bring more troubles than using Java directly.
Source
JPA
JPA (using Hibernate as implementation) is the default way to access and manage an SQL database in a standard Play Java application. It is still possible to use JPA from a Play Scala application, but it is probably not the best way, and it should be considered as legacy and deprecated.Source
Anorm(if you want to write ddl)
Anorm is Not an Object Relational Mapper so you have to manually write ddl. Source
Slick
Function relation mapping for scala .Source
Activate
Activate is a framework to persist objects in Scala.Source
Skinny
It is built upon ScalikeJDBC library which is a thin but powerful JDBC wrapper.Details1,Details2
Also check RDBMS with scala,Best data access option for play scala
We have a requirement in which we have to call a stored procedure from JPA (eclipselink) which takes list of oracle object as input.
Is there a way to achieve this?
EclipseLink does provide a way to pass Java Object to Stored Procedures.
http://wiki.eclipse.org/EclipseLink/Examples/JPA/PLSQLStoredFunction
and have a look at this as well
http://en.wikibooks.org/wiki/Java_Persistence/Advanced_Topics#Stored_Procedures_in_JPA_2.0
I have classes for entities like Customer, InternalCustomer, ExternalCustomer (with the appropriate inheritance) generated from an xml schema. I would like to use JPA (suggest specific implementation in your answer if relevant) to persist objects from these classes but I can't annotate them since they are generated and when I change the schema and regenerate, the annotations will be wiped. Can this be done without using annotations or even a persistence.xml file?
Also is there a tool in which I can provide the classes (or schema) as input and have it give me the SQL statements to create the DB (or even create it for me?). It would seem like that since I have a schema all the information it needs about creating the DB should be in there. I am not talking about creating indexes, or any tuning of the db but just creating the right tables etc.
thanks in advance
You can certainly use JDO in such a situation, dynamically generating the classes, the metadata, any byte-code enhancement, and then runtime persistence, making use of the class loader where your classes have been generated in and enhanced. As per
http://www.jpox.org/servlet/wiki/pages/viewpage.action?pageId=6619188
JPA doesn't have such a metadata API unfortunately.
--Andy (DataNucleus)