I have been working on EER diagram model for my Mysql base for the last 7 days. It is a rather complicated model with lots of connections and attributes. Now i know spring boot automatically creates tables based on your entity classes(including foreign keys and other settings) if you use spring.jpa.hibernate.ddl-auto = update in your application.properties, but is it possible to create entity classes after providing good credentials to DataSource object based on tables withing schema?
Point is i would probably need another 3-4 days of back-end coding to create all the classes with all the attribute, relationships etc.
Given the fact it can only be done in one correct way, based on schema tables and it is not really rocket science. Why not do the thing just once?
There is this question Automatically create Entities from database
but 1. i am using spring boot not JPA project and second blog is no longer active.
Any hints?
Just figured it out. I used the hibernate perspective in eclipse to connect to a database, create a cfg.xml and run the project as hibernate configurations, create a new reveng.xml config and that will work. More detailed answer can be found in the article below.
http://o7planning.org/en/10125/using-hibernate-tools-generate-entity-classes-from-tables
Hope it will help someone!!
There is this question Automatically create Entities from database but
1. i am using spring boot not JPA project and second blog is no longer active.
Under the woods, Spring boot uses JPA and more specifically Hibernate since it has bad compatibility with other JPA implmentations such as EclipseLink.
Why don't you use Dali Eclipse plugin ?
https://www.eclipse.org/webtools/dali/docs/3.2/user_guide/tasks006.htm
It has a wizard with many options and it addresses well this kind of need. The real drawback when I use it and we cannot store our orm configuration. So, since you have many tables, I advise you to generate it in an incremental way your entities.
Related
My database background comes from the Django framework (python). In Django, getting started with database migrations was easy: Django migrations. The Django framework provided tool for creating the migrations based on your models, and also a tool to apply the migrations on your database. I think this way of doing worked in both development and in production. You did not have to write migrations by yourself, the framework created them for you.
Now I have started a project with Spring Boot and Hibernate. I configure my application to use hibernate with JPA. With these settings, I now would need to know how does my framework handle database migrations? I mean if I change a column, either it's type, or even might remove it, then how do I migrate the database to the change? I know that spring boot will automatically detect column changes on startup, and create columns that do not exist based on the models (Entity's). I guess it has something to do with variable
spring.jpa.hibernate.ddl-auto
But how does it handle the existing database objects? Does it add the column to them too, and with what value? The default value I set? What if I change the column type? Can it then handle the change? These settings and spring-boot automated database management probably are not enough in the long run?
What I want to know is, that what are the best practices on how to handle database migrations with Spring Boot and hibernate combination? I believe there is a standard how most of the people with this combination handle the migrations? I hope it is as easy as with Django... I know about flyway, but don't know if I really need it, or if it is used much with this combination of mine (including spring boot and hibernate).
Liquibase or Flyway are the two main options for versioning/handling database migrations. ddl-auto is quick and dirty, but it does not, nor can it, take into account everything that needs to be handled. THere's also the chance of race-conditions (two instances trying to update the DDL at the same time).
This answer goes into more detail about ddl-auto in a production environment, and why you shouldn't.
Hibernate: hbm2ddl.auto=update in production?
https://www.credera.com/blog/technology-insights/java/liquibase-fed-inconsistent-schemas/ has bit more info on the why/concepts.
I'm new with Spring and I would like to use Spring Data with Jpa, Maven and Mysql in Eclipse environment. Then I'm going to use Tomcat as application server
I read a lot of tutorial but all of them are different from each other therefore don't understand what I have really to do. At the moment I'm confusing between these technology and DAO/DAL structure
Must I use Hibernate?
I have to use it with java JPA and then I have to add Spring data?
If anyone has an example or a tutorial I thank him.
Official spring data link
For spring-data-jpa,maven,mysql,hibernate,eclipse example tutorial
Hibernate is optional, it depends on your use case what you want to do. Its a ORM for mapping your db tables into java objects and have lot of other features like session caching, second level caching, criteria queries, validation, search/filters etc.
If you are just testing queries to load data you can use spring jpa queries directly, you will find examples in spring-data-jpa link
I have to modify design of the existing application according to following manner,
According to above design each project contains it's own schema and that mapping table (project_schema_table) is under main schema. All schemas are under one Postgresql database and in future users will create another new schemas (on demand) for their new projects.
Before displaying login window I have to list all existing projects and once user select his project I have to direct to that project with relevant schema. Other than main schema all other project base schemas are exactly the same.
This is a desktop application developed with latest versions of java technologies JavaFX, Spring and JPA with Postgresql database. Currently it has only one project related schema and I have to introduce main schema and all other subsequent project base schemas.
I have found similar stack overflow post but it didn't contains any solution. Whether I can accomplish this task with Spring AbstractRoutingDataSource ? or is there any other mechanism. Thanks.
The feature you are looking for is called Multi-Tenancy and Hibernate supports this out of the box from version 4.x onwards. Please see this post on how to use this feature.
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"
may i know in eclipse, is there any feature that will auto generate domain objects with all table relationship properly mapped in class?
can provide me with some reference articles on this?
You can use something like Hibernate to accomplish this
This plugin set for Eclipse called Hibernate Tools for Eclipse and ANT will do most of the work for you.
In particular it will do Reverse Engineering: The most powerful feature of Hibernate Tools is a database reverse engineering tool that can generate domain model classes and Hibernate mapping files, annotated EJB3 entity beans, HTML documentation or even an entire JBoss Seam application in seconds!
Telosys code generator does this kind of job.
It's an Eclipse plugin, it uses the database schema to create a light model
that is used to generate the Java code.
There are some predefined templates available on GitHub (for JPA, POJO, Documentation, Spring MVC, etc )
See http://www.telosys.org
and http://marketplace.eclipse.org/content/telosys-tools
Templates : https://github.com/telosys-templates-v3
Articles about code generation with Telosys :
https://modeling-languages.com/telosys-tools-the-concept-of-lightweight-model-for-code-generation/
https://dzone.com/articles/telosys-a-code-generation-tool-by-laurent-guerin
You can use Hibernate Tools 3.0.0.GA either via Eclipse or ANT to auto-generate your hibernate domain entities directly from your database tables.
See tutorial here :
http://docs.jboss.org/tools/3.0.0.GA/en/hibernatetools/html_single/index.html
I have a solution for you i.e to create auto generate domain objects with all table relationship properly mapped in class ...Try Dal4j yes you can find it in sourceforge.net/p/dal4j/wiki/ DAL4j is a Command Line and Framework tool that can be used to reverse engineer a MySQL or SQLServer database schema into a set of JPA Entity Beans.
DAL4j can be useful for scenarios where there is an existing database schema but a technology other that JPA is used by applications to interact with the database. DAL4j can provide an easy way to migrate your code base from other technologies such as JDBC or Hibernate to JPA.
The beans generated can be 1 or two types: Simple or Framework. Simple beans are standard pojo classes managed by your application using JPA semantics. Framework generated pojos use the DAL4j framework DAO generic to simplify CRUD operations.
DAL4j provides optional hooks to allow you integrate encryption/decryption of data fields that must be encrypted in the database.
Last, DAL4j provides a set of Generic classes that can be used to simplify creation of Session Beans which perform CRUD operations using generated Entities.
I think you will find this article feasible....
You want an object relational mapping of which Hibernate is the most popular for Java. The hibernate tools are typically better for taking annotated classes and using them to generate a schema, as opposed to vice versa, which is what you sound like you're doing. I suspect you'll be doing a lot of hand-annotating if you're working with a legacy DB schema.
if you use grails, you can generate domain objects with GRAG http://sourceforge.net/projects/grag
I use eclipse for java development, but when it comes to generating domain entities I use Net beans.
Create an EJB module, and then right click and generate entities.
You need to set up the database also you can select the tables you want visually.
Regards
Lyju
It feels like another rather common question that people always run into.
The link below links to a blog detailed enough for me to learn how to generate entities from database schema the first time.
http://shengwangi.blogspot.com/2014/12/how-to-create-java-classes-from-tables.html
Just in case, the following link refers to eclipse help page. This link should never expire:
http://help.eclipse.org/juno/index.jsp?topic=%2Forg.eclipse.jpt.doc.user%2Ftasks021.htm
I downloaded JBoss and failed to understand how it works. I think the plugin that I used is Hibernate Tools but I am not sure as I did not install any new plugin for this purpose. I am using Eclipse Luna for EE.
Hope this helps.
I got so tired of manually coding this kind of stuff so I made a tool to generate models, dao, and dao implementation from a schema. It's oriented towards spring boot and only tested on MySQL, but for those that don't want to use Hibernate and just want to work with jdbc/sql and JdbcTemplate, or just want POJOs with getter/setters generated for tables, then this could perhaps be something to kick off the coding.
Called Jassd (Java Automated Spring Source-code for Databases generator), I'm "jazzed" to introduce this tool: https://github.com/aforslund/jassd