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I'm a little bit confused on how the process of developping a database based application.
I'm using java language and Relational database.
What's the correct way of looping through the process of developping Object Oriented database based application like "inventory management control".
Developping database schema then doing OOD or Vice versa.
Since I assume you are about to use a traditional RDBMS, from my own experience, it'll be best to first design the database schema: think of all the tables you need to store your information, think of the relations between them (foreign keys).
The next step should be writing the application itself. I assume you're about to use Java, and can benefit from OOP design.
In such a case I strongly recommend using an ORM technology, like Hibernate, to fulfil the gasp between your OOP app design and RDBMS design. Though it's not obligated, since you can use simple JDBC approach.
From my experience, developing this way is much less time consuming than first design your high level OOP application, and then trying to fit a DB schema to it, because usually messing with DB is more time-expensive than with high level OOP abstraction.
There are a number of different approaches possible and they each have their merits and downside.
If you follow the ORM approach and use a tool like Hibernate you can hide much of the database implementation. You would proceed with your OOD and the database schema would drop out of that. ORMs like Hibernate even do the schema generation for you (this is very helpful in testing as you can create an in-memory database on the fly for your tests).
The advantages of this approach is that you can focus on the OOD and work with 'thin slices' where the database schema is generated as you progress. This fits in well with the agile approach.
The downside with the ORM approach is that it may not result in an optimised database schema. For example, the performance of your database schema may not be as good as if you had focused more on the schema design.
If you decide to focus on the database design you can spend time optimising it for performance and other non-functional requirements (like scalability and auditing). The downside with this approach is that it may restrict the way you do OOD in your code and it may be more difficult to work in the iterative fashion preferred by agile.
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A relative of mine wants me to to make a program to organize some information at where she works. It's fairly simple, however I don't know what kind of office drama they have going on, but she doesn't want to bother IT with all sorts of questions about the database that can be used, how it will connect (multiple people will read info stored in a database of some sort hosted within the companies intranet).
Anyways, I'm thinking it shouldn't be a problem to just use something like a local Microsoft access database file for now, and then rewrite the database component when I have more information. Is that an insane idea? This program is not hard, it can probably be written and tested in a week if I was working on it full time (I'm still in college). For that matter, I am thinking of using Java in Netbeans simply because I am comfortable with it. Should I worry that I find out they use some sort of database or other solution that cannot be (easily) worked with in Java?
While knowing a requirement like database type upfront is a good idea, being able to adapt to new requirements is a part of Agile development.
I'd argue it's not an insane idea. If you're careful about your design, switching out database won't be too bad. If you don't mind, I'll elaborate on a (possible) pattern that might save you trouble.
Overview
In my experience I have found it best to abstract the database logic (how to communicate) from the business logic (how to accomplish a task). These two layers are going to make your code much more maintainable for when you find out the company is running an Oracle database and not Access.
Data Access Layer
The DAL has one job and that is to communicate to the database. It needs to read, it needs to write, and that is it. Your classes will likely include information like table attribute names or queries. It's OK to do that here since the class is specific to a particular database. Using a DAL will greatly simply your database calls later on.
I would highly suggest looking into factory pattern for how to design these classes. Using factory pattern will completely decouple the Business Layer from the database specific classes using interfaces. In other words, you can completely change out the database without needing to modify the business logic.
Business Layer
In fancy terms, all I'm talking about is the logic for how to accomplish a task. The business layer doesn't have anything to do with where buttons appear on a screen nor should it worry about table names.
In this layer you will find yourself needing access to the database to read/write information and that is when you call on your Data Access Layer. It will handle the ugly details keeping your business logic from having to know what type of database your are using.
Data Transfer Object
Lastly, you're going to be pushing a lot of information between these layers. I suggest you design some classes that can help you transfer data that belongs together. Consider a call to the DAL requesting a book...
Book book = libraryAccessObject.getBookById("ABC123.45");
Getting a book is going to return a lot of information. Creating a book object to organize that information will make life easier.
In summary, it's not a far fetched idea but be careful with your design. Poor deign now could cause you a lot of problems next week. Layering your code will make it much more maintainable.
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I am building a web service using the Dropwizard framework (version 0.7.0). It involves executing some read-only queries to the database, manipulating the result set and then returning that data set. I am using MySQL as a database engine. Since I am new to this framework, I want to know which option I should choose: Hibernate or JDBI.
I've used both of these. I've used Hibernate with GORM in Grails as well as in a traditional Spring app and I've used JDBI in Dropwizard.
I have really enjoyed the simplicity of JDBI and here are a couple of reasons why I prefer it over Hibernate.
I know exactly what SQL is going to be executed to acquire the data I'm requesting. With Hibernate, you can sometimes have to do a lot of messing around with HQL and configuring your objects to what you intended to have returned. You ultimately resort to SQL, but then have the difficultly of properly mapping your results back to your domain objects, or you give up and allow hibernate to fetch them one by one.
I don't need to worry about lazy/eager fetching and how that is going to affect my query time on large data sets.
Mappings aren't complicated because you manage them on your own and you don't have to rely on getting the right combinations of annotations and optimizations.
For your case in particular, it sounds like you'd want something lightweight because you don't have a lot of use cases and that would definitely be JDBI over Hibernate in my opinion.
Really, both of these solutions are just "lock-in".
If you want to go with a persisted model type interface, write your code against JPA (if you are sure it's only going to back to a relational database) or JDO (if you might want to back to relational and other-type databases, like the no-SQL movement). This is because with either of these solutions, when problems occur you can switch persistence providers without rewriting the bulk of your code.
If you want to go with a procedural persistence model (dealing with SQL queries directly and such), then go with JDBi or perhaps even JDBC. JDBi provides a very nice abstraction over JDBC; however, there are cases where you want the lower level access (for performance reasons, of the kind were you are tuning the queries and database in concert). Again JDBC is a standard such that you can swap out one database for another with some ease; however, the SQL itself won't be as easy to swap out.
To amend the SQL swap out problems, I recommend using sets of property files to hold the queries, and then a Resource loader type mechanisim to bind the SQL for the right database to the code. It isn't 100% foolproof; but it does get you a bit further.
Now, if you ask me what I'd use, I highly recommend JDO.
if you have very few work upon database then use JDBI else go for Hibernate as it is very strong and provide many additional features to your persistence logic.
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My team is working on a medium size application (OLTP style). We were interested by switching to JPA instead of only using JDBC queries. Mostly for performance and practical reason. I'm not looking for a tutorial that shows me how to create a persistence.xml or Entity class in Eclipse. What i would like to know is what would be the steps to convert all the database queries into the JPA format. I know that the whole application must use JPA.
Many programmers has worked on this project over the years, so not everyone has the same SQL knowledge or the same programming skills. So there must be in this application 1000+ customs queries, using multiple tables (something that native JPA does not support very well), or query that is selecting only a few fields in a table... This is getting a bit out of control and i think that JPA would create a nice toolbox to make sure that everyone is going the same direction.
What should i look for to make sure that i'm not going into a process (convertion) that will never end ? Some sort of guideline.
(Again, i'm not looking for programming exemples, nor Eclipse tutorial.)
Thanks!
First step is convert you database schema into database model using JPA, you need to be clear what are the table, sequences, database objects that you are using in your existing application and start modeling all the schema with JPA you should consider use JPA annotation.
The step above will determine what will be your entities, embeddables and mapped superclass, their properties and the relationships they have, this step is very crucial as your logic will depends on the correctness of this model.
Then start looking for all the queries that are involved in your project, as you said that you have 1000+ queries consider use two scenario, convert all of them in JPQL queries or use a mix between native queries and named queries, I really prefer to convert all in JPQL unless are very database dependent. A step you must follow is find all of them, probably are some existing tool that convert from SQL to JPQL but I believe is better idea make by your own.
Once you have queries and model for the database start the creation of your new DAO using JPA and EntityManager stuff, I should recommend extract the interface for your exisiting DAO and start moving to a JPA implementation using the same interface, this will avoid break some code on your own, don't forget unit and IT test for your new DAO.
Also with the above approach you could start moving the application module by module, DAO or by DAO does not require to move full application at once. This will give you a kind of process in which you will see some progress each time you finish a new DAO or module.
Not sure what you mean about programming examples, I think those are the required steps but each project is different from each other, so consider this as some kind of guidelines.
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I currently have an application, where it's primary performance issue is using file-based database consisted of JSON responses.
I'd like to rewrite my application to use SQLite database feature.
Since I'm lazy, I'd like to use some kind of ORM.
So far I have found only two big ORM libraries:
ORMLite
GreenDAO ORM
DB4O
ActiveAndroid
My primary goal is to raise performance on working with data as much as possible
But I've found two possible issues with those libraries.
ORMLite uses annotations, which is big performance issue in pre-honeycomb due to this bug
GreenDAO is using some kind of code generator, and that would slow me down on development as I would have to write generator, and then use generated code. And I don't very like this idea.
DB4O is JPA, which I've always considered as slow and heavy on memory usage, therefore unsuitable for low-end devices (remember the Android API v7)
ad #ChenKinnrot:
The estimated load should be sufficient to think about using an ORM.
In my case it is about 25-30 unique tables, and at least 10 table joins (2 - 4 tables at a time). About 300-500 unique fields (columns)
So my questions are:
Should I use ORM/JPA layer in Android application?
If so, what library would you recommend me to use? (and please add some arguments too)
I've used ORMLite and found it straightforward once you got the hang of it (a few hours), quite powerful and didn't cause any performance problems (app tested in Gingerbread on HTC desire and HTC Hero).
I will be using it again in any projects I need to use a DB for.
A ORM layer is appealing.
However, in practice I either write simple ORM myself or use the Content Provider paradigm, which does not cooperate well with ORM.
I have looked into some existing ORM libraries (mainly ORMLite ,activeAnroid) but they all scared me away
as they seems not so easy to get started.
"We're talking about 25-30 unique tables, and at least 10 table joins.
About 300-500 unique fields (columns)"
If you have fixed and limited patterns of how the data will be queried, I would recommend to write the ORM/sql yourself.
My 2 cents.
If you are worried about your app's performance, I'd recommend greenDAO. It will save you from writing lots of boring code, so code generation should not be an issue. In return, it will generate also entities and DB unit tests for you.
I got some knowledge to share so:
ORM by definition is slower than writing your own sql, it's suppose to simplify the coding of data access, and provide a generic solution, generic = runs slower than you write your queries, if you know sql well.
The real question is how good performance you want to get, if it's the best possible, don't consider any data mapping framework, only sql generation framework that will help you write stuff faster, but gives you full control of everything.
If you don't want to get the most out of the sql db, use orm, I got no experience with this orm you mentioned, so I can't say what to choose.
And your DB is not so big and complex so the time you'll save with orm is not an issue.
In my experience, I had a lot of benefits from using ORM engines. However, there was the case when I had to deal with performance problems.
I had to load about 10 000 rows from the database, and with a standard implementation (I was using ORMLite), it took about 1 minute to complete (depends on the device CPU).
When you need to read a lot of data from the database, you can execute plain SQL and parse the results yourself (in my case, I only needed to query for 3 columns from the table). ORMLite also allows you to retrieve raw-results. By this, the performance has increased by 10 times. All 10 000 rows were loaded in 5 seconds or less!
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In the last time I heard a lot of complaining about Hibernate. And indeed I have some painful experiences with Hibernate too. So I read about Ebean and Siena.
Both have interesting approaches. Unfortunately, database access layers are very easy to write, but if your project grows and you have to handle great database-tables, you know if they are good or not. So it's really difficult to evaluate such a tool. Hibernate is well known and you could be sure that you can solve your problem with it. Sometime you need to learn a lot, but you can solve it.
How is it with Ebean? Are there any real world applications? Which databases are supported? Is it reliable?
After searching a little bit more I see that there are a lot more ORM-frameworks, so is there at least one reliable one?
Rob (Ebean Committer) here.
Ebean is about 4+ years old now. I would say it is fairly mature now. The supported DB's include Oracle, MySql, Postgres, H2 and SQL Server (and recently SQLite). Ebean is doing stuff that other ORM's are not such as Autofetch (automatic query tuning) so I'm not how that fit's into a 'maturity rating'. IMO the Ebean community is relatively small though so you probably need to hit the Ebean google group to engage them.
Any real world applications? Yes, but you are best to ask the Ebean community about that really. Certainly there is good support for batch processing (batch size, turn of cascading persist for a transaction etc) and large query support that I don't see in JPA etc (you might get something similar with Hibernate's Sessionless support).
Hopefully this might answer some small parts of your question anyway.
Cheers, Rob.
I'm currently a developer of Siena but not since very long. Let me explain why I became a developer on this project?
I went to Siena because I wanted to use Play+GAE and Siena appeared to be a good start for GAE DB and I really wanted to avoid JDO/JPA.
Then, I began to really appreciate Siena for its straightforward, light and easy approach and so simple APIs. It doesn't pretend to be the all-in-one abstraction layer like JDO and the greatest standard DB API like JPA. It really made me think of DB APIs from Python/Ruby and it really fits my point of view: I want a simple DB API which allows me to solve the great majority of my problems and when I have a more complex problem, I will use the lower layer APIs but certainly not an abstraction layer such as hibernate.
The possibility to make my code work on GAE DB or JDBC was also a good aspect. Once again, Siena doesn't pretend to provide exactly the same things in both worlds because SQL and NoSQL are not really compatible (but ORM is neither really compliant to SQL model :) ).
But once again, it is quite practical to be able to rely on the same APIs in several DBs.
Finally, the library is ONE jar and you don't have to retrieve the whole universe to use it.
So, I became progressively a committer on Siena because I wanted to take part of this nice little adventure.
Now siena team is working on a new version keeping the same simple APIs, bringing new interesting features and really improving all the backend code to make it even easier to extend for new DB support.
Siena is a pragmatic API driven by user experiences and that's why I like it ;)
Pascal
We've had really great experience with MyBatis, which is not an ORM per se, but another class of persistence manager, an SQL Mapper. Using it you start with SQL statements and direct it on how to map result rows into POJOs. It's conceptually easy to understand and tune with not much magic going on inside. It's ideal if you are comfortable with SQL or need to work with an established schema.
Besides Ebean and Siena:
You can try JIRM which is focused on CRUDing immutable objects (yes I'm the author).
There is also jOOQ and Joist.
I feel that JIRM minimizes the number of DTO's because the domain objects are immutable and do not inherit, implement and/or are not "enhanced/instrumented". Such is not the same with Siena and Ebean.
Also because the objects are Immutable there is more of a focus on per column updating instead of the whole object which makes more sense given today's AJAX interfaces (compared to the old POST the whole bean model).
What about using EB3, with for instance JBoss (www.jboss.org)?