As the application gets complicated, one thing that change a lot is the queries, especially if they are complex queries. Wouldn't it be easier to maintain the queries in the db rather then the resources location inside the package, so that it can be enhanced easily without a code change. What are the drawbacks of this?
You can use stores procedures, to save your queries in the database. Than your Java code can just call the procedure from the database instead of building a complex query.
See wikipedia for a more detailed explanation about stored procedures:
https://en.wikipedia.org/wiki/Stored_procedure
You can find details about the implementation and usage in the documentation of your database system (MySql, MariaDb, Oracle...)
When you decide to move logic to the database, you should use a version control system for databases like liquibase: https://www.liquibase.org/get-started/quickstart
You can write the changes to you database code in xml, json or even yaml and check that in in your version control system (svn, git...). This way you have a history of the changes and can roll back to a previous version of your procedure, if something goes wrong.
You also asked, why some people use stored procedures and others keep their queries in the code.
Stored procedures can encapsulate the query and provide an interface to the data. They can be faster than queries. That is good.
But there are also problems
you distribute the buisiness logic of your application to the database and the programm code. It can realy be troublesome, if the logic is spread through all technical layers of your applicaton.
it is not so simple anymore to switch from a Oracle database to a MariaDb, if you use specific features of the database system. You have to migrate or rewrite the procedures.
you have to integrate liquibase or another system into you build pipeline, to keep track of you database changes.
So it depends on the project and it's size, if either of the solutions is better.
every website I can find seems biased to praised objectdb over hibernate and mysql. Example, http://www.jpab.org/ObjectDB/ObjectDB/server/Hibernate/MySQL/server.html.
Are there any disadvantages to using objectdb instead of hibernate and mysql for java web services? I am of course using JPA.
You mean are there advantages and disadvantages of using an ODBM against an RDBMS ? There are ample refs on the web that address that.
With particular respect to JPA, it is designed around RDBMS syntax, and so it is likely that some query sintaxis will not be fully supported in an object datastore (whether ObjectDB or any other). This may mean that some queries either throw an exception or evaluate in-memory (and that may mean speed). On the other hand it may be quicker at some persistence ops. Obviously you will not get anything like the number of people available who know about that datastore if you have problems, whereas with MySQL there are many thousands.
Also there are many JPA implementations available for persisting to MySQL, and they all have their own advantages and disadvatanges. Hence this questions is way too open ended, and is just going to search for personal opinion rather than anything specific fact based
I wag going through a hibernate tutorial, where they say that hibernate is not suitable for data centric application. I am very much impressed by the 'object oriented structure' it gives to the program, but my application is very much data centric(it fetches and updates huge number of records. But I dont use any stored procedures). Cant I use hibernate?Are there any wrappers written over hibernate, which I can use for my application?Any help is appreciated.
I am not sure about specific meaning of phrase data centric. Aren't all database applications data centric? However, if you do process tons of data, Hibernate may not be the best choice. Hibernate is best to represent object models mapped to the database and it may have role in any application, but to do ETL (extract/transform/load) tasks you may need to write very efficient SQL by hand.
In principal you can, but it tends to be slow. Hibernate more or less creates an object for every row retrieved from the database. If you do this with large volumes of data, performance takes a serious hit. Also updates on many rows using a single update have only very basic support.
A wrapper won't help, at least with the object creation issue.
There are many advantages of using Hibernate, when one gets their object model correct as a developer there is a lot of appeal in interacting with the database via objects but in practice I have found initially Hibernate is great but becomes very frustrating when you come against issues like performance and fault finding.
When it comes to decision on the DA (Data Access) layer I ask myself this question.
Am I writing an application which has a requirement to run an different databases?
If the answer is yes then I will consider an (ORM) like Hibernate.
If its no then I will normally just use JDBC normally via Spring.
I feel that interacting with the database via JDBC is a lot more transparant and easier to find faults and performance tune.
I have a thick client, java swing application with a schema of 25 tables and ~15 JInternalFrames (data entry forms for the tables). I need to make a design choice of straight JDBC or ORM (hibernate with spring framework in this case) for DBMS interaction. Build out of the application will occur in the future.
Would hibernate be overkill for a project of this size? An explanation of either yes or no answer would be much appreciated (or even a different approach if warranted).
TIA.
Good question with no single simple answer.
I used to be a big fan of Hibernate after using it in multiple projects over multiple years.
I used to believe that any project should default to hibernate.
Today I am not so sure.
Hibernate (and JPA) is great for some things, especially early in the development cycle.
It is much faster to get to something working with Hibernate than it is with JDBC.
You get a lot of features for free - caching, optimistic locking and so on.
On the other hand it has some hidden costs. Hibernate is deceivingly simple when you start. Follow some tutorial, put some annotations on your class - and you've got yourself persistence. But it's not simple and to be able to write good code in it requires good understanding of both it's internal workings and database design. If you are just starting you may not be aware of some issues that may bite you later on, so here is an incomplete list.
Performance
The runtime performance is good enough, I have yet to see a situation where hibernate was the reason for poor performance in production. The problem is the startup performance and how it affects your unit tests time and development performance. When hibernate loads it analyzes all entities and does a lot of pre-caching - it can take about 5-10-15 seconds for a not very big application. So your 1 second unit test is going to take 11 secods now. Not fun.
Database Independency
It is very cool as long as you don't need to do some fine tuning on the database.
In-memory Session
For every transaction Hibernate will store an object in memory for every database row it "touches". It's a nice optimization when you are doing some simple data entry. If you need to process lots of objects for some reason though, it can seriously affect performance, unless you explicitly and carefully clean up the in-memory session on your own.
Cascades
Cascades allow you to simplify working with object graphs. For example if you have a root object and some children and you save root object, you can configure hibernate to save children as well. The problem starts when your object graph grow complex. Unless you are extremely careful and have a good understanding of what goes on internally, it's easy to mess this up. And when you do it is very hard to debug those problems.
Lazy Loading
Lazy Loading means that every time you load an object, hibernate will not load all it's related objects but instead will provide place holders which will be resolved as soon as you try to access them. Great optimization right? It is, except you need to be aware of this behaviour otherwise you will get cryptic errors. Google "LazyInitializationException" for an example. And be careful with performance. Depending on the order of how you load your objects and your object graph you may hit "n+1 selects problem". Google it for more information.
Schema Upgrades
Hibernate allows easy schema changes by just refactoring java code and restarting. It's great when you start. But then you release version one. And unless you want to lose your customers you need to provide them schema upgrade scripts. Which means no more simple refactoring as all schema changes must be done in SQL.
Views and Stored Procedures
Hibernate requires exclusive write access to the data it works with. Which means you can't really use views, stored procedures and triggers as those can cause changes to data with hibernate not aware of them. You can have some external processes writing data to the database in a separate transactions. But if you do, your cache will have invalid data. Which is one more thing to care about.
Single Threaded Sessions
Hibernate sessions are single threaded. Any object loaded through a session can only be accessed (including reading) from the same thread. This is acceptable for server side applications but might complicate things unnecessary if you are doing GUI based application.
I guess my point is that there are no free meals.
Hibernate is a good tool, but it's a complex tool, and it requires time to understand it properly. If you or your team members don't have such knowledge it might be simpler and faster to go with pure JDBC (or Spring JDBC) for a single application. On the other hand if you are willing to invest time into learning it (including learning by doing and debugging) than in the future you will be able to understand the tradeoffs better.
Hibernate can be good but it and other JPA ORMs tend to dictate your database structure to a degree. For example, composite primary keys can be done in Hibernate/JPA but they're a little awkward. There are other examples.
If you're comfortable with SQL I would strongly suggest you take a look at Ibatis. It can do 90%+ of what Hibernate can but is far simpler in implementation.
I can't think of a single reason why I'd ever choose straight JDBC (or even Spring JDBC) over Ibatis. Hibernate is a more complex choice.
Take a look at the Spring and Ibatis Tutorial.
No doubt Hibernate has its complexity.
But what I really like about the Hibernate approach (some others too) is the conceptual model you can get in Java is better. Although I don't think of OO as a panacea, and I don't look for theoritical purity of the design, I found so many times that OO does in fact simplify my code. As you asked specifically for details, here are some examples :
the added complexity is not in the model and entities, but in your framework for manipulating all entities for example. For maintainers, the hard part is not a few framework classes but your model, so Hibernate allows you to keep the hard part (the model) at its cleanest.
if a field (like an id, or audit fields, etc) is used in all your entities, then you can create a superclass with it. Therefore :
you write less code, but more importantly ...
there are less concepts in your model (the unique concept is unique in the code)
for free, you can write code more generic, that provided with an entity (unknown, no type-switching or cast), allows you to access the id.
Hibernate has also many features to deal with other model caracteristics you might need (now or later, add them only as needed). Take it as an extensibility quality for your design.
You might replace inheritance (subclassing) by composition (several entities having a same member, that contains a few related fields that happen to be needed in several entities).
There can be inheritance between a few of your entities. It often happens that you have two tables that have pretty much the same structure (but you don't want to store all data in one table, because you would loose referential integrity to a different parent table).
With reuse between your entities (but only appropriate inheritance, and composition), there is usually some additional advantages to come. Examples :
there is often some way to read the data of the entities that is similar but different. Suppose I read the "title" field for three entities, but for some I replace the result with a differing default value if it is null. It is easy to have a signature "getActualTitle" (in a superclass or an interface), and implement the default value handling in the three implementations. That means the code out of my entities just deals with the concept of an "actual title" (I made this functional concept explicit), and the method inheritance takes care of executing the correct code (no more switch or if, no code duplication).
...
Over time, the requirements evolve. There will be a point where your database structure has problems. With JDBC alone, any change to the database must impact the code (ie. double cost). With Hibernate, many changes can be absorbed by changing only the mapping, not the code. The same happens the other way around : Hibernate lets you change your code (between versions for example) without altering your database (changing the mapping, although it is not always sufficient). To summarize, Hibernate lets your evolve your database and your code independtly.
For all these reasons, I would choose Hibernate :-)
I think either is a fine choice, but personally I would use hibernate. I don't think hibernate is overkill for a project of that size.
Where Hibernate really shines for me is dealing with relationships between entities/tables. Doing JDBC by hand can take a lot of code if you deal with modifying parent and children (grandchildren, siblings, etc) at the same time. Hibernate can make this a breeze (often a single save of the parent entity is enough).
There are certainly complexities when dealing with Hibernate though, such as understanding how the Session flushing works, and dealing with lazy loading.
Straight JDBC would fit the simplest cases at best.
If you want to stay within Java and OOD then going Hibernate or Hibernate/JPA or any-other-JPA-provider/JPA should be your choice.
If you are more comfortable with SQL then having Spring for JDBC templates and other SQL-oriented frameworks won't hurt.
In contrast, besides transactional control, there is not much help from having Spring when working with JPA.
Hibernate best suits for the middleware applications. Assume that we build a middle ware on top of the data base, The middelware is accessed by around 20 applications in that case we can have a hibernate which satisfies the requirement of all 20 applications.
In JDBC, if we open a database connection we need to write in try, and if any exceptions occurred catch block will takers about it, and finally used to close the connections.
In jdbc all exceptions are checked exceptions, so we must write code in try, catch and throws, but in hibernate we only have Un-checked exceptions
Here as a programmer we must close the connection, or we may get a chance to get our of connections message…!
Actually if we didn’t close the connection in the finally block, then jdbc doesn’t responsible to close that connection.
In JDBC we need to write Sql commands in various places, after the program has created if the table structure is modified then the JDBC program doesn’t work, again we need to modify and compile and re-deploy required, which is tedious.
JDBC used to generate database related error codes if an exception will occurs, but java programmers are unknown about this error codes right.
While we are inserting any record, if we don’t have any particular table in the database, JDBC will rises an error like “View not exist”, and throws exception, but in case of hibernate, if it not found any table in the database this will create the table for us
JDBC support LAZY loading and Hibernate supports Eager loading
Hibernate supports Inheritance, Associations, Collections
In hibernate if we save the derived class object, then its base class object will also be stored into the database, it means hibernate supporting inheritance
Hibernate supports relationships like One-To-Many,One-To-One, Many-To- Many-to-Many, Many-To-One
Hibernate supports caching mechanism by this, the number of round trips between an application and the database will be reduced, by using this caching technique an application performance will be increased automatically
Getting pagination in hibernate is quite simple.
Hibernate has capability to generate primary keys automatically while we are storing the records into database
... In-memory Session ... LazyInitializationException ...
You could look at Ebean ORM which doesn't use session objects ... and where lazy loading just works. Certainly an option, not overkill, and will be simpler to understand.
if billions of user using out app or web then in jdbc query will get executed billions of time but in hibernate query will get executed only once for any number of user most important and easy advantage of hibernate over jdbc.
In the old days we used to access the database through stored procedures. They were seen as `the better' way of managing the data. We keep the data in the database, and any language/platform can access it through JDBC/ODBC/etc.
However, in recent years run-time reflection/meta-data based storage retrieval mechanisms such as Hibernate/DataNucleus have become popular. Initially we were worried that they'd be slow because of the extra steps involved (reflection is expensive) and how they retrieve unnecessary data (the whole object) when all we need is one field.
I'm starting to plan for a large data warehousing project that uses J2EE, but I'm a bit unsure whether to go for Stored Procedures or JDO/JPA and the like. Recently, I've been working with Hibernate, and to be quite honest, I don't miss writing CRUD stored procedures!
It essentially boils down to:
Stored procedures
+ Can be optimised on the server (although only the queries)
- There's likely to be more than a thousand stored procedures: add, delete, update, getById, etc, for each table.
JDO
+ I won't spend the next few months writing parameters.add("#firstNames", customer.getFirstName()); ...
- Will be slower than SPs (but most support paging)
What would you plump for in my situation. In this case I think it's a much of a muchness.
Thanks,
John
"JDO - Will be slower than SPs (but most support paging)"
This assumption is often false. There's no reason for SP's to be particularly fast. I've done some measurements and they're no faster than code outside the database.
A data warehouse is characterized by insert-only loads and long-running SELECT...GROUP BY... queries.
You're not writing OLTP transactional processing. You're not using 3NF as a way to prevent update anomalies on update/delete transactions.
Since you're doing bulk inserts, a SP will definitely be slower than a bulk load utility. Bulk loaders are often multi-threaded and will consume all available CPU resources. The SP is part of the DB and can only share limited DB resources.
Since you're mostly doing SELECT GROUP BY, a SP won't help much here, either. The SELECT statement doesn't benefit from being wrapped in a procedure.
You don't need them. They don't help.
You can easily benchmark a bulk-load and a query to demonstrate that SP's aren't helping.
Rod Johnson in his "J2EE Design adn Development" wrote a very clear analysis about ORM/StoredProcedures. He said that
Stored procedures should only be used in a J2EE system to perform operations that will always use the database heavily, whether they're implemented in the database or in Java code that exchanges a lot of data with the database.
As you're planning to implement a datawarehouse, I think that the stored procedures approach is the right choice.
I would suggest using the metadata to generate the scripts you use for loading into the data warehouse. This allows you to get performance benefits from using specialised load tools and perhaps from stored procedures (if you're using a sufficiently ancient database). Also, you will probably end up hand coding at least some SQL. Having your generic scripts done as stored procs will allow you to schedule all of them in the same way and not have to worry about changing how they are invoked when you rewrite some generated code to make it run better.
As for getting the data out, if what you're building in J2EE is a reporting tool, then you may be better off using JDO. While I'm not terribly familiar with the reporting side of things, one benefit I can see is that it will be easier to allow your end users to make custom reports that you did not anticipate in advance (although you've still got to have some limits on what they can do so that they don't take down the database in the process).