I have a definition for a column like that:
#Column
private String my_column;
And by default in Postgres database type for this field is character varying(255).
Now, I want to change the data type for this column.
How I can do this without entry in database and alter table?
I tried this:
#Lob
#Column
private String my_column;
And
#Column(columnDefinition = "TEXT")
private String my_column;
But, without results.
The thing is, that JPA does not handle Schema changes.
JPA maps your existing DB to Java Classes, it does not manage the database it self.
As for schema changes managment.
A common practice is to have a schema migration tool to handle that, for example Flyway and Liquibase are a popular solutions.
There you can write a SQL script, to change the DB column type to "text"
and it will apply those changes when you run the DB migration process.
Or you can always just access your DB and modify it manually.
Related
The only link I found that's close to what I am experiencing is this one :
How do you synchronize the id of a java object to its associated db row?
and there's not much of a solution in it.
My problem is that my Java objects aren't updated after being added to my database despite the .commit()
em.getTransaction().begin();
System.out.println(eleve.getID());
em.persist(eleve);
em.getTransaction().commit();
System.out.println(eleve.getID());
which refers to this class
public class Eleve {
private String _nom;
private String _prenom;
private float _ptsMerite;
#Id
private int _IDEleve;
and yields this output :
0
0
I think I've done everything properly when it comes to the persistence since it does create the object in the database (mySQL) with correct ID's which I've set to be autoincrement.
I am using javax.persistence for everything (annotations and such).
Did you try to add the #GeneratedValue annotation at your ID field?
There are four possible strategies you can choose from:
GenerationType.AUTO: The JPA provider will choose an appropriate strategy for the underlying database.
GenerationType.IDENTITY: Relies on a auto-increment column in your database.
GenerationType.SEQUENCE: Relies on a database sequence
GenerationType.TABLE: Uses a generator table in the database.
More info: https://www.baeldung.com/jpa-strategies-when-set-primary-key
If you ever change to a more powerful framework it is likely that this manages your transactions (CMT) so you can't (or don't want) commit everytime you want to access the ID for a new entity. In these cases you can use EntityManager#flush to synchronize Entity Manager with database.
I have a column in a MySQL database defined as LONGBLOB. This is the java code used on its mapping:
#Type(type = "org.hibernate.spatial.GeometryType")
#Column(columnDefinition = "LONGBLOB")
private Point latlng;
I want now to share this definition in an HSQLDB (for in-memory testing), but unfortunately HSQLDB doesn't have the LONGBLOB type.
I know about the HSQLDB alternatives such as LONGVARBINARY, but how I can instruct Hibernate to use LONGBLOB on MySQL and LONGVARBINARY on HSQLDB?
(I can't replace the #Column with #Lob; I tried that and Hibernate uses by default a "geometry" type instead of "longblob". Changing the current MySQL mapping is not an option.)
XML mappings with orm.xml overwrites annotated mappings.
So, you could include XML mapping file for this entity in /src/test/resources/ and define the proper datatype for this column.
I'm trying make an entity work with Oracle (11.2) and PostgreSQL(9.4) in a Spring Boot (1.4.4) application.
My entity contains a long text field (over 4000 characters).
The appropriate data type in Oracle is CLOB and the corresponding type in PostgreSQL is TEXT.
I'm able to make it work with PostgreSQL
#Column(name = "LONG_TEXT", columnDefinition="TEXT")
private String longText;
However it would fail with Oracle in hibernate validation stage since CLOB requires #Lob annotation.
The following code works with Oracle
#Lob
#Column(name = "LONG_TEXT")
private String longText;
However this time it fails when reading from PostgreSQL with the following exception:
PSQLException: Large Objects may not be used in auto-commit mode
Stack overflow suggests performing queries in transactions. Disregarding questionable requirement to invoke transaction in select queries, adding #Transactional to query methods didn't help.
Any thoughts are more than welcomed.
The solution we came to is to adopt the #Lob and #Transactional approach.
The main issue was with the placement of the #Transactional annotation, causing the PSQLException. Once fixed, we were able to work with both types of DBs.
I've wasted too much time on this ...
I'm using oracle and I have a sequence (MY_TABLE_SEQ) defined which increments by 1.
In my Pojo I have:
#SequenceGenerator(name = "MY_SEQ", sequenceName="MY_TABLE_SEQ", allocationSize=50)
#GeneratedValue(strategy=GenerationType.SEQUENCE, generator="MY_SEQ")
This gives me a unique constraint issue. From my understanding I need to set the following property:
hibernate.id.new_generator_mappings=true
I've tried setting in my hibernate.cfg.xml file but it does not seem to make any difference. I've come across server post to place in persistance.xml but this is a standalone app, no webcontainer.
Setting allocationSize=1 works but of course it hits the db on each insert to get the next sequence. Setting the above property is suppose to resolve it.
I haven't tried Oracle, but I had similar issues to yours inserting into an AS400 DB2 table.
I had to remove the identity flag on the id column on DB2 table - and instead used a custom jpa/hibernate sequence generator. This is set up on the pojo/entity annotation of the #ID entity field as you've done.
DB2 had been giving me errors about missing SYSIBM.SYSSEQUENCES table, so evidently hibernate (version 5.2), doesn't recognize the native DB2 identity designation. A custom sequence was and effective workaround.
On the #ID entity field:
#GeneratedValue(generator = "table", strategy=GenerationType.TABLE)
#TableGenerator(name = "table", allocationSize = 20)
This example allocates a pool of 20 sequence numbers each time it queries the table.
Next, create the required table Hibernate needs with columns that match the hibernate5 API - must be in lower case ... so put quotes around the names to work around the auto-upper casing that DB2 defaults to. The API will error out if these names are in caps.
Table:
"hibernate_sequences"
example of 2 Columns used:
"sequence_next_hi_value" (integer, not nullable, 0 default)
"sequence_name" (character, sample length 20, not nullable, natural default)
In the configuration code for the dialect used - ex: Spring Boot programmatically, add these properties:
properties.put("hibernate.supportsSequences","false");
properties.put("hibernate.id.new_generator_mappings","false");
and in the *.properties file:
spring.jpa.properties.hibernate.dialect.supportsSequences=false
spring.jpa.properties.hibernate.id.new_generator_mappings=false
Database systems are case-sensitive for schema/table/field names. Also watch for typos everywhere, incl. property names.
Be sure your pojo/entity only contains private fields that will be mapped to the table. Static finals such as serialVersionUID are ok.
I will be doing someething similar for SQL Server soon.
For MySQL, I had no issues using an identity column as defined in a table ID field to insert records, so didn't have to make all these changes. A simpler setup since hibernate recognizes the identity designation in MySQL.
#GeneratedValue(strategy=GenerationType.IDENTITY)
was all that was needed in the pojo.
I'm a newbie at all this, so always looking for better ways ... but this worked for now.
I set the property like this in the hibernate.cfg.xml file and it works !
<property name="hibernate.jpa.compliance.global_id_generators" value="true"/>
I am using liquibase:diff to update my database if one entity is modified.
How can I do in my Java entity if I want to transform VARCHAR(255) to TEXT in the MySQL column type.
In Java I only have a String type for my property.
Thank you.
If you're using JPA/Hibernate annotations, you can do this
#Column(columnDefinition = "TEXT")
but this would be database specific, and not portable across databases which don't have a "TEXT" column type.
A more portable solution would be to use the #lob annotation like
#Lob
private String text;
this should generate TEXT or LONGTEXT data type.