I am making a web app with Spring Boot. I am planning on using Spring Data JPA (Hibernate) connected to MySQL. One question I have is that I have already written out the SQL statements to create my database schema. I have my primary keys, foreign keys, relationships all set already. All the tutorials I've seen assume you don't have tables or anything in the database already. If I create entities, how can I ensure they match up to my already existing data model?
I don't mind recreating the entities by hand, since there's not that many classes and manually reverse-engineering won't take too much time. (I have seen a way to reverse engineering using Eclipse but I prefer to use IntelliJ, also I feel that manually writing the Entities may be easier than doing the reverse process.) But I want to make sure that the entity objects I create will match the tables I already have and won't cause trouble. I'm not sure what the best way to go about doing this is. Will Hibernate overwrite my existing schema when I run for the first time?
You can make hibernate to validate your mapping.
Set this property :
hibernate.hbm2ddl.auto=validate
I am trying to make a web application in Spring 4(Java Configuration). I am using postgres as database and C3P0 as connection pool.
All my database transactions are happening in postgres stored procedures/ functions. I am using Hibernate #NamedNativeQueries to call the stored procedures.
I have 2 questions:
1. My application will have multiple users logged in at same time. SO should i use sessionFactory.openSession() or sessionFactory.getCurrentSession() for getting hibernate session?
2. shall i use hibernate to call stored procedures or build in support in spring mvc4? i know both ways but i am more comfortable with hibernate as it needs very less efforts compared to spring way but i feel hibernate is making my application slow but not sure.
Please help me in finding answers to these questions.
Answer to the first question :
you should have a session per user connected. For example, if you are in a servlet context, you can have a servlet filter to call sessionFactory.openSession() per servlet thread.
Answer to the second question :
performance and optimisation is not a feeling. If you feel hibernate slow, measure it and try to know why. You have to measure where it slows. You can also try both solutions with a simple example and know where you feel more comfortable.
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We have been using JDBC for a very long time in our web applications. The main reason we used it is because we have 100% control over the code, sql and fix things by our hands. Apart from that we used triggers inside the database, and the database is developed separately by DB experts.
However many now recommend using Hibernate so we also thought about using it. But, we found the below issues.
Hibernate cannot connect with an "Existing" database. It always try to create a one of its own.
Our database might access by same application which is in different platforms (cloud, server, VPS, Personal Computer). Hibernate can make problems because of its caching in this situation.
We never like to give the "table creating work" to the java code. We create tables manually, always.
We might have to use very long and complex SQL statements. Last time we used an statement with more than 150 lines, joining more than 20 tables. We doubt whether we will face troubles in this when it comes to Hibernate.
Our SQL code is nice and standard. Hibernate generated code seems to be bit dirty for us.
We always use MySQL. Never use any other DB.
The application we create require max security, related to medical. If at least one data record is leaked, we are done.
There are lot of foreign keys, Primary Keys, Composite Keys, Unique Keys etc etc in database. In forums, some complained that Hibernate messed with those.
We decided to try hibernate because some people claims, "Are you Software Engineers? You are using already dead JDBC !!. "
Considering these, please let me know whether the above points are actually true (as I said, I got to know them via googling, discussion etc) or not. And, what are the pros and cons of Hibernate VS Java JDBC?
Answering issues listed above:
1. Hibernate cannot connect with an "Existing" database. It always try to create a one of its own.
This is wrong. Hibernate can connect to an existing database, and it doesn't always try to recreate it. You just should turn of parameter like hbm2ddl. auto.
2. Our database might access by same application which is in different platforms (cloud, server, VPS, Personal Computer). Hibernate can make problems because of its caching in this situation.
Hibernate has an adjustable cache, so this is also not a problem.
3. We never like to give the "table creating work" to the java code. We create tables manually, always.
No problem. See p.1 above. Furthemore there are several convinient libraries for indirect table creation and update (e.g. liquibase) which can be used in couple with hibernate perfectly.
4. We might have to use very long and complex SQL statements. Last time we used an statement with more than 150 lines, joining more than 20 tables. We doubt whether we will face troubles in this when it comes to Hibernate.
You can always use direct JDBC calls and invoke native SQL queries via hibernate, if it is neeeded.
5. Our SQL code is nice and standard. Hibernate generated code seems to be bit dirty for us.
Again, if you have to invoke some logic complicated SQL code instead of hibernate auto-generated - you can do it.
6. We always use MySQL. Never use any other DB.
Not a problem at all. Hibernate has special MySQL dialect support: org.hibernate.dialect.MySQLDialect.
7. The application we create require max security, related to medical. If at least one data record is leaked, we are done.
Security issues aren't related to ORM techniques. Hibernate is just logical and convinient object-oriented layer between pure database JDBC calls and programmers tools. It doesn't influence somehow on common net security.
Hibernate is a great tool and you'll find plenty of documentation, books, and blog articles about it.
I will address all your concerns:
Hibernate cannot connect with an "Existing" database. It always tries to create one of its own.
Hibernate should use a separate database schema management procedure even for integration testing. You should use an incremental versioning tool like FlywayDB to manage your schema changes.
Our database might access by same application which is in different platforms (cloud, server, VPS, Personal Computer). Hibernate can make problems because of its caching in this situation.
You don't have to use the 2nd level cache, which uses 3rd party caching implementations. All caching solutions may break transactional consistency. The first level cache guarantees session-level repeatable reads and with the optimistic locking in place you can prevent lost updates.
We never like to give the "table creating work" to the java code. We create tables manually, always.
The DB should be separated from your ORM tool. That's a best practice anyway.
We might have to use very long and complex SQL statements. Last time we used an statement with more than 150 lines, joining more than 20 tables. We doubt whether we will face troubles in this when it comes to Hibernate.
Hibernate is great for write operations and for concurrency control. You still need to use native SQL for advanced queries (window functions, CTE). But Hibernate allows you to run native queries.
Our SQL code is nice and standard. Hibernate generated code seems to be bit dirty for us.
You don't need and you shouldn't probably use the hbmdll utility anyway.
We always use MySQL. Never use any other DB.
That's even better. You can therefore use advance native queries without caring for database portability issues.
The application we create require max security, related to medical. If at least one data record is leaked, we are done.
Hibernate doesn't prevent you from securing your database or the data access code. You can still use database security measures with Hibernate too. You can even use Jasypt to enable all sorts of security-related features:
advanced password hashing
two-way encryption
There are lot of foreign keys, Primary Keys, Composite Keys, Unique Keys etc etc in database. In forums, some complained that Hibernate messed with those.
All of those are supported by Hibernate. Aside from the JPA conventions, Hibernate also offers particular mapping for any exotic mapping.
We decided to try hibernate because some people claims, "Are you Software Engineers? You are using already dead JDBC !!. "
That's not the right argument for switching from a library you already master. If you think you can benefit from using Hibernate then that's the only compelling reason for switching from JDBC.
Using plain old JDBC, does not mean you are lacking in IT industry, rather Hibernate also uses JDBC in the underlying layer.
What advantages it gives us what we should look for.
1.) Cache Mechanism.
2.) Managing sessions, transactions etc.
3.) Reduce efforts in writing queries, more utilities of hibernate like Query API, Criteria API, HQL
The questions that you have raised are more or less covered in Hibernate docs.
Also there are lot more caching strategy available ehcache, infinispan, depends on the server we are deploying, JBOSS, Weblogic, Tomcat etc. ++ environment like cloud, distributed cache etc.
Hibernate still provides you with option of turning off automatically creating schema and pointing to the one create by you.
Here are the quick answers that I know
1) You can connect to an existing database. But yeah as stated here
If you don't have a solid object model, I'd say that Hibernate is a
terrible choice.
2) As you database is been accessed from different applications so you can maintain locks. On-the-other-hand you can trun-off caching as done here.
3) You can create tables manually and connect it using .hbm.xml file.
4) You can use any type of query in hibernate like simple SQL queries criteria.
5) You can directly use SQL code in Hibernate, if you want. Other option is to use criteria.
6) Hibernate is NOT DB specific. You can go for any Database and connect it with hibernate.
7) Using locks and giving rights in database you can maintain security.
8) Agreed that foreign keys are messy in Hibernate If You Donot Handle It Well. So Use OO approach and maintain cascades well, then Hibernate will be good choice.
I am using Hibernate's multi-tenancy feature via JPA, with a database per tenant strategy. One of my requirements is to be able to run a query against a table that exists in each database but obviously with different data. Is this possible?
Thanks in advance for your time.
Nope. this is not possible because when hibernate runs queries it is already initialized with a connection. MT support in Hibernate is basically done a little "outside of Hibernate" itself. It's kind of feeding hibernate with a proper connection and when it's fed :) it's bound to that connection.
If you need cross-tenant queries you might want to reconsider multitenancy or change JPA provider to the one that support "shared schema approach" e.g. EclipseLink. With shared shema approach you have two choices:
run native query agains table containing mt-aware entities
create additional entity - dont mark it as multitenant - map it to the table containing mt-ware entities and run JPQL query in standard manner
I have a Java web application which uses Hibernate for storing data into the database and retrieving them.
The strategy I am currently using is to load everything from the database on to the application at start up, and saving/updating them to the database as the user interacts with the application.
What I have also done is to keep track of Transaction history for each user as part of the business logic. (So this transaction history is all loaded on application start up).
The problem I can see is that I shouldn't load all the transaction history for all the user, because if there are a lot of the Transaction history, and users might not necessarily need to see them, then that could be a lot of memory being used up, so it is not efficient.
I was wondering if there is something similar to what PHP script can do, which is just query the database only when user request to see the transaction history, and so it is not using the server resource. (Asides from query the database) Or what are some suggestions/comments regards to what I am facing right now.
Thank you.
Query Hibernate when you need a given piece of information and let Hibernate manage putting it back to the database. This will allow Hibernate to manage the caching.
Note, that when using Hibernate, you should let Hibernate manage the data completely. Do not add or change data yourself using raw SQL.
If you are using a modern container, you should consider migrating to JPA as it is the standard in Java EE containers, allowing you to be more flexible when you need to scale. JPA is very close to Hibernate, but is an API, not an implementation, so you have more than one to choose from.
why not query hibernate for every request come in and release after response? This is a common approach.