im building a Spring Boot web app with MySQL and till now i used the
spring.jpa.hibernate.ddl-auto=create-drop
in my properties file, and now i want to move to production and i cant use this line anymore because as u all know its saving the data on the memory and the worst thing its destroying all the data and create a new table every deploy.
for dev purposes its wonderful but what i need to do next cause i want it to behave exactly as i was on the ddl-auto but to persistently save the data and most inportantly never to drop the data.
P.S. the hibernate.ddl-auto has nothig to do with the JPA Repository?
cause i use Crud Repository alot and i need this to continue working with Crud Repository, will it?
the best thing to do, according to me, is:
use the option spring.jpa.hibernate.ddl-auto=create-drop to create
the DB schema and the default data (if any) in development environment
export the created DB schema in a normal DDL
give the DDL to DBAs to check if any improvement must be done (e.g.
add some indexes, review some FK etc..)
adapt JPA models after DBAs review
give the final DDL to the "production DBAs" in order to create the
final correct schema in production environment too
Regarding to your question:
the hibernate.ddl-auto has nothig to do with the JPA Repository? cause
i use Crud Repository alot and i need this to continue working with
Crud Repository, will it?
You can of course use the crud repository; this option will not influence your business logic
I hope it's useful
Angelo
You don't want to be sending DDLs around. You will end up trying to invent version control system for your scripts, by naming them specifically or putting them in folders, you will struggle communicating with DBAs, scripts breaking..
You want your database definition code to be a part of your code base so you can put it under version control (yes, git).
Try to use Liquibase for this. It will help you do automatic updates of the schema, data, everything db related, and it knows how to migrate your app's db, lets say, from 1.1 to 1.2 but also from 1.1 to 1.6. There are also other db migration tools like Flyway, you can look them up and play around.
Related
We have a java application which uses spring boot and hibernate.
There are many changes on entities and fields. That's why, I want to follow changes and rollback mechanism. So that, I need a version control system over database. I checked flyway and liquibase, but I think those don't solve my problem. Because my table creations and updates are handled by hibernate.
Is there any way to see which queries are executed by hibernate to change the database and which changes have occurred since the latest database change (I mean new table, column creation or refactoring)?
One way to do it (how we do it):
Use 2 databases. A reference database and a development database.
On the development database use hibernate to let it create the strucutre.
Once a development cycle is done you run liquibase diffChangelog on the reference database. It will create a changelog.xml with all changes that have been done by hibernate on the development db. Manually correct it (names, etc).
When your happy with changelog file and the development cylce is done apply the changelog onto the reference database.
Start your next development cycle and repeat.
That way you can combine the advantages of letting hibernate generate the schema and still use liquibase to have a versioned DB-Schema that is re-creatable.
Use those tools as those are dedicated for this purpose. Personally, I like Liquibase more but it's your choice.
Hibernate's schema creation mechanism should not be used in production as then your Java description of the entity would drive the creation of the tables resulting in an inefficient structure.
That feature is only there for testing purposes.
I have a much used project that I am working on currently updating. There are several places where this project can be installed, and in the future it is not certain what version is used where and to what version one might be updated to in the future. Right now they are all the same, though.
My problem stems from the fact that there might be many changes to the hibernate entity classes, and it must be easy to update to a newer version without any hassle, and no loss of database content. Just replace WAR and start and it should migrate itself.
To my knowledge Hibernate does no altering of tables unless hibernate.hbm2ddl.auto=create, but which actually throws away all the data?
So right now when the Spring context has fully loaded, it executes a bean that will migrate the database to the current version by going through all the changes from versionX to versionY (what version it previously was is saved in the database), and manually alter the table.
It's not much hassle doing a few hard-coded ALTER TABLE to add some columns, but when it comes to adding complete new tables, it feels silly to have to write all that...
So my question(s) is this:
Is there any way to send an entity class and a dialect to Hibernate
code somewhere, and get back a valid SQL query for creating a table?
And even better, somehow create an SQL string for adding a column to a table, dialect-safe?
I hope this is not a silly question, and I have not missed something obvious when it comes to Hibernate...
have you tried
hibernate.hbm2ddl.auto=update
it retains all the database with the data and append only columns and tables you have changed in entity.
I don't think you'll be able to fully automate this. Hibernate has the hbm2ddl tool (available as an ant task or a maven plugin) to generate the required DDL statements from your hibernate configuration to create an empty database but I'm not aware of any tools that can do an automatic "diff" between two versions. In any case you're probably better off doing the diff carefully by hand, as only you know your object model well enough to be able to pick the right defaults for new properties of existing entities etc.
Once you have worked out your diffs you can use a tool like liquibase to manage them and handle actually applying the updates to a database at application start time.
Maybe you should try a different approach. In stead of generating an schema at runtime update, make one 'by hand' (could be based on a hibernate generated script though).
Store a version number in the database and create an update script for every next version. The only thing you have to do now is determine in which version the database currently is and sequentially run the necessary update scripts to get it to the current version.
To make it extra robust you can make a unit/integration test which runs every possible database update and checks the integrity of the resulting database.
I used this method for an application I build and it works flawlessly. An other example of an implementation of this pattern is Android. They have an upgrade method in their API
http://developer.android.com/reference/android/database/sqlite/SQLiteOpenHelper.html#onUpgrade(android.database.sqlite.SQLiteDatabase, int, int)
Don't use Hibernate's ddl. It throws away your data if you want to migrate. I suggest you take a look at Liquibase. Liquibase is a database version control. It works using changesets. Each changeset can be created manually or you can let Liquibase read your Hibernate config and generate a changeset.
Liquibase can be started via Spring so it should fit right in with your project ;-)
We are doing a project in which we have planned to use JPA Persistence. We think that once the project goes live, there is a small chance that changes in the data model might be required.
My query is that what are the different strategies available to handle such a change. Particularly I have following questions:
With updated JPA classes, what are the best practices to incorporate them in the existing database schema?
With JPA, are there any best practices to, archive old data, update database schema, and again migrate the database to the new schema?
What are the various kinds of changes (broadly speaking) that will make such a migration impossible?
In RHQ (http://rhq-project.org/ ) we have some dbutils that have a schema description in XML that serves to populate the initial schema on an empty database and then another xml file that registers changes to this base schema as individual "diffs" of DDL and DML statements.
Whenever a JPA class is changed (in a schema relevant way), both XML files are updated. On the next run of the installer, it will look at the existing database, gather its version and then play all the update steps from the version in the DB to the most current one.
This dbutils code is available in git.
There are other frameworks around like liquibase that can help you here.
You can also take a look at this framework:
http://flywaydb.org
Advertised as: "The agile database migration framework for Java"
In my experience, migrations are not the problem (hibernate can do them automatically), but rollbacks are, if you are dealing with destructive changes. For example, if you remove a column, there's no way to rollback that change, unless you have the data from that column backed up somewhere. Best way do such backups probably depends on your DB vendor.
I was learning some JPA to teach to some java friends and I was wondering, how do you handle updates that comes after the creation of the db in JPA? Let's say I have a production environment where there's data that I cannot lose.
Some changes comes in and how do I apply that on my production environment? It there a way that JPA would only update the changes on the database?
Or do I need to manually create a SQL script to update my database?
Is there any other options?
[]'s
Rodrigo Dellacqua
Some changes comes in and how do I apply that on my production environment? It there a way that JPA would only update the changes on the database?
Nothing standardized. In other words, that would be a provider specific feature. For example, Hibernate has a SchemaUpdate tool that can (in theory) safely update a database schema. In practice, many don't use that on a production database (including me).
Or do I need to manually create a SQL script to update my database?
Using migration scripts (and maybe a database migration tool) is IMO the safe way to handle this and is the way to go on real life projects.
And again, some migration tools might provide support for a given JPA provider. For example, liquibase does offer Hibernate support and can diff your Entities against a database to generate a change script.
I'm currently working on a desktop application using JPA/Hibernate to persist data in a H2 database. I'm curious what my options are if I need to make changes to the database schema in the future for some reason. Maybe I'll have to introduce new entities, remove them or just change the types of properties in an entity.
Is there support in JPA/Hibernate to do this?
Would I have to manually script a solution?
I usually let Hibernate generate the DDL during development and then create a manual SQL migration script when deploying to the test server (which I later use for UAT and live servers as well).
The DDL generation in Hibernate does not offer support for data migration at all, if you only do as much as adding a non-null field, DDL generation cannot help you.
I have yet to find any truely useful migration abstraction to help with this.
There are a number of libraries (have a look at this SO question for examples), but when you're doing something like splitting an existing entity into a hierarchy using joined inheritance, you're always back to plain SQL.
Maybe I'll have to introduce new entities, remove them or just change the types of properties in an entity.
I don't have any experience with it but Liquibase provides some Hibernate Integration and can compare your mappings against a database and generate the appropriate change log:
The LiquiBase-Hibernate integration records the database changes required by your current Hibernate mapping to a change log file which you can then inspect and modify as needed before executing.
Still looking for an opportunity to play with it and find some answers to my pending questions:
does it work when using annotations?
does it require an hibernate.cfg.xml file (although this wouldn't be a big impediment)?
Update: Ok, both questions are covered by Nathan Voxland in this response and the answers are:
yes it works when using annotations
yes it requires an hibernate.cfg.xml (for now)
There are two options:
db-to-hibernate - mirror DB changes to your entities manually. This means your DB is "leading"
hibernate-to-db - either use hibernate.hbm2ddl.auto=update, or manually change the DB after changing your entity - here your object model is "leading"