I would like to know which alternatives exist to replace DDL utils from Apache.
I ask this because ddlutils project seams to be Dead, and also it does not support H2 Databases. I've searched for it, and I found suggestions like liquidbase or flyway.
My problem is: These frameworks run when project starts and change DB structure based on some XML files. They are really designed for Database Migration.
What I want is a framework to CREATE/ALTER Tables in Runtime, in a high abstraction level., i.e. supportting at least Mysql, Sqlserver, oracle, and H2.
For example I could tell to the engine that I want to create a table with a Field AGE with Type Number, and the framework would rephrase to:
create table MY( id bigint(20))
create table MY(id bigint)
create table MY (id, number)
depending on the underlying db engine.
Any suggestions?
I could see there is a patch for ddlutils, for it to support H2. However I wasn't able to patch my svn checkout...
Any help will be appreciated.
thanks in advance
rui
I know this is an old thread, but wanted to give a definitive answer.
Yes, DdlUtils is dead, hasn't seen an update in 2 years now.
However, it looks like the guys might have switched over to https://www.symmetricds.org. Their repo is https://github.com/JumpMind/symmetric-ds.
As soon as you scratch away at the surface, you'll find that the core of DdlUtils is still in there (even has some of the old Apache copyright notices).
Class names have changed, APIs have changed so there is not a 1-to-1 mapping, but it is getting regular updates and includes H2 and other database support. Honestly I'd rather be getting those things instead of keeping the old APIs.
You're not going to find a guide on using Symmetric DS in the same way as the old DdlUtils doco, but there is enough in the code that you should be able to piece it together.
Take a look on jOOQ it is very useful in generating DDL (and DML too)
create.createTable("table")
.column("column1", INTEGER)
.column("column2", VARCHAR(10).nullable(false))
.constraints(
constraint("pk").primaryKey("column1"),
constraint("uk").unique("column2"),
constraint("fk").foreignKey("column2").references("some_other_table"),
constraint("ck").check(field(name("column2")).like("A%"))
)
.execute();
This looks promising: https://bitbucket.org/aragot/play-sql-dialects/src
At least as a start.
Mogwai ERD designer might help though they do not formally support H2 but you could put H2 into compatibility mode with one of the supported DB systems: https://sourceforge.net/p/mogwai
Related
For the majority of the examples and tutorials I have seen it is always suggesting to execute SQL to Delete the table if it exists in the onUpgrade method.
Why would you want to delete the table as this would remove all the data, would it not be better to just replace the old DB version with the new version?
This would something that I could not understand and no where online outlined the reason.
Thanks
| Sam |
For simplicity. Dropping the old version and recreating a new version is simple and straightforward, though also destructive. In many cases, data loss like this is not a concern at development time.
Writing proper data migration code would be a topic for another example/tutorial as it inherently involves at least two versions of the database schema and thus the database helper. Including migration example in a simple do-this-to-get-started tutorial would just add unnecessary complexity.
Because they are tutorials: they assume you have no valuable data in them (or no data at all). In that case, the easiest way to upgrade a schema is to remove old tables and creating the new ones.
Don't take in mind it, you are right.
I got the following problem and no idea on how to solve it.
I am using SqlJet to access and manage a small Sqlite DB.
It's amazing the simplicity of this library! But now, I have to execute a complex query which cannot be expressed using the methods provided by the library. On the website, they say
SQLJet does not support SQL queries; there is an API to work with the
database on a lower level
And I was wondering, anybody of you know what is this lower level API to execute SQL queries?
As far as I can tell from my research, there is no support for arbitrary SQL queries in SQLJet. I first thought it was a sqlite wrapper, which it isn't, so there is also no way to use JDBC.
Other than the lookup rows by name and index stuff, the "lower level" API they are talking about on their page, seems just to be direct access to the internal DB representation, as mentioned in this post.
From a quick glance at the JavaDoc and sources, it might be the SqlJetDb.getSchema() and getTable() methods. There is no proper API documentation or Tutorials, there is even a complaint about this in the issue tracker.
Maybe you can describe what you want to do. Either there is a way to do it though the limited interface SQLJet offers, or I'm afraid I can't help.
Its also good idea to contact the developers directly, as it seems there is not much information to be found elsewhere.
I have with me a java app that uses mysql-- now I have converted the database to SQL Server- but I need to convert the code of the java app so that it now uses SQL Server.
This java app uses Struts and Hibernate
What all things do I have to keep in mind to make this conversion?
hibernate should make the transition seamless for you.
Make sure to choose the correct driver as some drivers might act differently.
I personally like jtds. It has vast documentation.
Look for native queries in your code because they might need some modifications.
Other than that, I don't think you should experience any problem.
I had an application that supported oracle, SQL-Server and mysql and we didn't have specific code for each one.
EDIT : as maba suggests in the comments, you will need to modify the hibernate configuration a bit (driver, dialect, url ).
For more hibernate specific configuration, I found a great stackoverflow answer
I'd like to save persistent objects to the file system using Hibernate without the need for a SQL database.
Is this possible?
Hibernate works on top of JDBC, so all you need is a JDBC driver and a matching Hibernate dialect.
However, JDBC is basically an abstraction of SQL, so whatever you use is going to look, walk and quack like an SQL database - you might as well use one and spare yourself a lot of headaches. Besides, any such solution is going to be comparable in size and complexity to lighweight Java DBs like Derby.
Of course if you don't insist absolutely on using Hibernate, there are many other options.
It appears that it might technically be possible if you use a JDBC plaintext driver; however I haven't seen any opensource ones which provide write access; the one I found on sourceforge is read-only.
You already have an entity model, I suppose you do not want to lose this nor the relationships contained within it. An entity model is directed to be translated to a relational database.
Hibernate and any other JPA provider (EclipseLink) translate this entity model to SQL. They use a JDBC driver to provide a connection to an SQL database. This, you need to keep as well.
The correct question to ask is: does anybody know an embedded Java SQL database, one that you can start from within Java? There are plenty of those, mentioned in this topic:
HyperSQL: stores the result in an SQL clear-text file, readily imported into any other database
H2: uses binary files, low JAR file size
Derby: uses binary files
Ashpool: stores data in an XML-structured file
I have used HyperSQL on one project for small data, and Apache Derby for a project with huge databases (2Gb and more). Apache Derby performs better on these huge databases.
I don't know exactaly your need, but maybe it's one of below:
1 - If your need is just run away from SQL, you can use a NoSQL database.
Hibernate suports it through Hibernate OGM ( http://www.hibernate.org/subprojects/ogm ).
There are some DBs like Cassandra, MongoDB, CouchDB, Hadoop... You have some suggestions Here
.
2 - Now, if you want not to use a database server (with a service process running always), you can use Apache Derby. It's a DB just like any other SQL, but no need of a server. It uses a singular file to keep data. You can easily transport all database with your program.
Take a look: http://db.apache.org/derby/
3 - If you really want some text plain file, you can do like Michael Borgwardt said. But I don't know if Hibernate would be a good idea in this case.
Both H2 and HyperSQL support embedded mode (running inside your JVM instead of in a separate server) and saving to local file(s); these are still SQL databases, but with Hibernate there's not many other options.
Well, since the question is still opened and the OP said he's opened to new approaches/suggestions, here's mine (a little late but ok).
Do you know Prevayler? It's a Java Prevalence implementation which keep all of your business objects in RAM and mantain Snapshots/Changelogs in the File System, this way it's extremely fast and reliable, since if there's any crash, it'll restore it's last state and reapply every change to it.
Also, it's really easy to setup and run in your app.
Ofcourse this is possible, You can simply use file io features of Java, following steps are required:-
Create a File Object
2.Create an object of FileInputStream (though there are ways which use other Classes)
Wrap this object in a Buffer object or simply inside a java.util.Scanner.
use specific write functions of the object created in previous step.
Note that your object must implement Serializable interface. See following link,
I want to migrate my data from one DB to other using Java. Both DBs have different schema structure. I might also need to define some mapping / validation rule. Can anyone please guide me about any strategy, framework or any opensource project.
Thanks
Isn't in this case I have to create all the POJO to match the both schema (even by auto generating). Is there any way to avoid this thing i.e. giving schema mapping and generating POJO on fly in memory ?
Any idea?
Thanks
Yes, you need an Extract-Transform-Load (ETL) tool.
Here are some open source choices:
http://www.google.com/search?gcx=w&sourceid=chrome&ie=UTF-8&q=open+source+etl
ETL is generally used for this as in duffymo's answer.. you could also try ORM tools for this:
There is the Torque project.. http://db.apache.org/torque/
Read the data from your existing schema into java objects, then set them into the other objects for the other schema and then save them into the database. I am pretty sure hibernate also can be used, although I havent used hibernate per se. It works on the same way as torque..