I have some problem with hibernate. when I add a column age into the file mapping of Client.xml, hibernate update my table client and add the column, but when a delete the same column age from Client.xml and client.java, and I run my application, I found that the column still in my table client.
can anyone have a clue why hibernate couldn't delete the column age from table client
thank you ^_^
Hibernate follow two approach
1. Schema first
2. Code first
In Schema first Java entities are created based on your database design and in Code first approach database is created with all java entities annotated with #Entity.
In your case you are following Code first approach, when you add any new column in java entity hibernate will create column on your behalf if hibernate.hbm2ddl.auto is update. if your database contains more tables hibernate has no issue with it that's why hibernate is not deleting any column if you delete it from Java Entity.
Related
Is there any way to change the column property from unique=true to unique=false without dropping the table?
Now I am stuck in the situation where tables has been created earlier and these table are containing data too. When I changed unique=true to unique=false it doesn't making any changes in table.
You can easily do this thing in the database. Suppose I have a table Person with Person_name having a unique constraint.
ALTER TABLE Person
DROP INDEX Person_name;
or
ALTER TABLE Persons
DROP CONSTRAINT Person_name;
If you try to achieve the same thing using hibernate, hibernate will try to drop and create the table again, which you do not want to happen.
Hmm... I don't know if you can allow yourself on database drop but you can try in your application properties file use:
spring.jpa.hibernate.ddl-auto=update
or
spring.jpa.hibernate.ddl-auto=create-drop
For more info:
https://docs.spring.io/spring-boot/docs/current/reference/html/howto-database-initialization.html
Also if you know that you will have a lot of changes in database schema and you want to make it easy to work you should get familiar with
https://www.liquibase.org/
Hibernate won't update to implement constraints on the table because there is a possibility of having an error as the existing table might have inconsistencies.
I am new to hibernate and am using xml file for mapping. I want to map more than 8 tables, is it possible or not ?
I am using mysql for DB. In all that mapping examples they use maximum 3 tables in mapping. If I change the value in one table that has to reflect it on to next one.
For Example I am giving the Username in my Employee Table and use that one in my login table. If I am mapping 2 tables it means, the username in employee table can automatically update to my login table. Is this correct ?
And how many tables am I able to map in single xml file.
A hibernate component may be your solution. Also hibernate definitions can be in separate files and hibernate will figure it out.
https://www.google.com/search?q=hibernate+components
is there any method to support my mapping anyways in Hibernate?
I mean to correct my mapping automatically, when changs in Database were made?
The best would be that hibernate woud conform to DB, so DB is leader and Hibernate only maps and dont make any changes.
Example:
Yesterday a Table named "Phones" had the columns:
id
Number
Today that table got a Update and now it looks like:
id
Number
customerID
PhoneListId
is there any option that hibernate correct this automatically?
i changed some of my entity classes. I added some more columns and changed some of column names. I want to learn that how can i update my sql tables according to these entities or how can i re-create these tables from my entity classes.Thanks for your help.
add this line in hibernate mapping:
<property key="hibernate.hbm2ddl.auto">create</property>
but your app would be recreate your table each time you start app.
Also you can read this chapter
I'm interested in getting the "Description" property of a table column. Is it possible to do via Hibernate? I'm using Sql Server 2008.
Edit: I'm trying to map the column description found in information_schema to the corresponding column (JPA column entity)
I think the simplest solution would be mapping of informatio_schema in way that will provide the information for columns. If you are using annotations you easily can access to information like Table name and Column name, that can be used in Criteria to fetch the description.
This is probably re-coding some available feature and non platform depend. But if you will not succeed in research is always some solution.