I am planning to use Spring JdbcTemplate to access my database. Is it a must to use spring-data-jdbc when using JdbcTemplate? The reason I am asking is I don't need "entity"(POJO) for my table in my application. Would it add some overheads if I use spring-data-jdbc?
You can use the JdbcTemplate without Spring Data JDBC without a problem.
JdbcTemplate existed for many years before Spring Data JDBC was conceived.
Spring Data JDBC does involve an overhead.
It extracts data from POJOs, creates queries and transforms the result back to POJOs.
Of course all that takes resources.
If you don't need/benefit from it don't use it.
You can also start with JdbcTemplate and later start using Spring Data JDBC without a problem if the need arises.
JdbcTemplate is part of the spring-jdbc module, so you only need that (and sprint-tx, which includes the DataAccessException hierarchy).
spring-data-jdbc adds support for (not surprisingly) spring-data on top of spring-jdbc. So you don't need it to use JdbcTemplate, the same as you don't need spring-data-jpa to use the JPA EntityManager.
Spring-data-jdbc is implemented on the basis of spring-jdbc. If you don't need Entity at all, then using spring-jdbc to interact directly with the database is the most convenient and flexible. In this case, using spring-data-jdbc is just a pure increase in learning costs. Spring-data-jdbc is designed for DDD (Domain Driven Design) mode, which is different from the current mainstream programming model. The learning cost is not low...
Related
Im not sure if i can use Spring Data JDBC also for complex models. My doubts arise especially cause in the Spring Data JDBC (3.0) documentation is written:
"There is a simple model of how to map entities to tables. It probably only works for rather simple cases. If you do not like that, you should code your own strategy. Spring Data JDBC offers only very limited support for customizing the strategy with annotations." https://docs.spring.io/spring-data/jdbc/docs/3.0.0/reference/html/#jdbc.why
I was expecting Spring Data JDBC is also working for more complex cases.
The limitations that rise from this simple model affect mostly legacy projects where you have a database that you maybe can't even change.
Spring Data JDBC is not intended to map an arbitrary database model to an arbitrary Java domain model, but to use a Domain Driven Design approach and construct the database accordingly.
But even in the cases where you hit the limitations of Spring Data JDBC you can always fall back on Springs JdbcTemplate without any conflict with the rest of your model which gets persisted by Spring Data JDBC.
The same is not true for JPA. Of course you can use JdbcTemplate with JPA as well, but you now have to very different approaches to persistence in your application which can and will interact in interesting ways due to JPA caching and dirty checking.
I therefore think Spring Data JDBC is an excellent choice for large application and complex models.
It's limitations will push you in the direction of better defined smaller modules and less complex models.
I created user in oracle database and I am trying to create session but I find many ways in spring boot so what is the easy way if I want to create classe connections using the Username and Password ?
You can jdbc template, spring data JDBC or spring data JPA, well depending on your use case.
If your data model is quite complex, you should avoid using the JDBC template as you will need to write prepared statements which can be cumbersome. JPA will allow you to use object-oriented programming principles and also will help you map the entities to your database columns.
For example, if you are going to use spring data JPA, you need to set the application properties as follows:
spring.datasource.type=oracle.oracleucp.jdbc.UCPDataSource
spring.datasource.oracleucp.connection-factory-class-name=oracle.jdbc.pool.OracleDataSource
spring.datasource.oracleucp.sql-for-validate-connection=select * from dual
spring.datasource.oracleucp.connection-pool-name=UcpPoolBooks
spring.datasource.oracleucp.initial-pool-size=5
spring.datasource.oracleucp.min-pool-size=5
spring.datasource.oracleucp.max-pool-size=10
This would behind the scene create an Oracle Datasource. In this example, we are using Oracle Universal Connection Pooling. You can also use HikariCP which is quite popular.
check this out
If you want to use UCP with above properties then you must have SpringBoot version higher than 2.4.0.
Check out the Spring Boot code sample on GitHub.
Is it possible to use Hibernate and RDBMS(Mysql, Postgres etc) with ReactiveCrudRepository instead of CrudRepository? I have tried some samples with Spring Data Jpa and Hibernate, but couldn't get it done. I was only able to find a few samples on ReactiveCrudRepository for MongoDB and cassandra.
Is it possible to use Hibernate and Mysql with ReactiveCrudRepository instead of CrudRepository?
TL;DR:
Not with Hibernate and MySQL, but with R2DBC and Postgres, Microsoft SQL Server or H2.
Take a look at Spring Data R2DBC.
Long Version
Why not JPA?
With Hibernate/JPA included this won't happen in the foreseeable future.
JPA is based on the idea that you load part of your data model into memory, manipulate the resulting object model and let JPA transform these changes.
All this within a single transaction.
This is kind of the opposite how one deals with a reactive store where you try to make atomic changes and try to decouple the loading, processing and storing and all this without blocking.
Why not JDBC?
So we have to look at the technology level below JPA: JDBC.
But JDBC is still blocking: You send a SQL statement to your database and then JDBC will block until you get the result.
And again this goes against the idea of reactive: Never block.
One could wrap this in a thread pool to mitigate this to some extent, but that is more of a workaround than a solution.
Why R2DBC?
There are some suitable drivers for some databases that could be used for reactive repositories.
But they are proprietary and thereby not a good basis for something that really should eventually work across all (relevant) relational databases.
For some time the Spring Data team hoped that ADBA would fill that gap.
But discussions on the mailing list made it clear that ADBA was not aiming for reactive but only for asynchronous.
Again not what we needed for a reactive repository abstraction.
So early in 2018 various people living at the intersection or reactive and relational decided that we need a standard for reactive database access.
R2DBC (Reactive Relational Database Connectivity)
is a proposal for such a standard.
The hope is that it either helps convincing Oracle to move ADBA to a reactive approach or if that doesn't happen it becomes the standard itself.
And with already three implementations available chances for the second option look promising.
R2DBC itself is mainly an SPI, i.e. an API that is to be implemented by database providers.
The SPI is designed in a way that puts minimal requirements on implementers.
But this also makes R2DBC somewhat cumbersome to use.
The idea is that other libraries will step up and build libraries designed for usability on top of that SPI, as it happened with JDBC.
Spring Data R2DBC
Spring Data R2DBC is one such library and it offers what you asked for: Support for ReactiveCrudRepository although it is independent of JPA/Hibernate and there is no support for MySQL yet.
State of the projects
Both R2DBC and Spring Data R2DBC didn't have a production release yet and it will take at least several months to get there.
Spring Data R2DBC just released the first milestone.
See the release article for its current capabilities.
R2DBC is on its 6th milestone. See the release article for details.
See also this answer: Why does Spring not provide reactive (non-blocking) clients for relational databases?
Original answer as a reference for archeologists:
As of now (Jan 2017) it is not possible.
The currently relevant release for the reactive part of Spring Data is Spring Data Kay M1 (You can check if there is a newer version available on the project home page)
And a blog post from the Spring Data team about that release and specifically the reactive parts in it starts with (emphasis mine):
Spring Data Kay M1 is the first release ever that comes with support for reactive data access. Its initial set of supported stores — MongoDB, Apache Cassandra, and Redis — all ship reactive drivers already, which made them very natural candidates for such a prototype.
The reason is that there is no standard non-blocking way to access a relational database. So only those that support this kind of API are supported right now.
One could implement a ReactiveCrudRepository using JPA or JDBC and delegate the work to a thread pool. This would provide an async API on the outside, but would still consume the resources for the Threads and block between independent data accesses, so only a small part of the benefits of the reactive approach would get realized.
Hibernate started a new Hibernate Reactive subproject for reactive streams support which provides Hibernate/JPA similar APIs to access RDBMS. But unfortunately at the moment, Spring Data does not support it. So there is no a ReactiveCrudRepoisoty for Hibernate Reactive.
But you can integrate Hibernate with Spring yourself and get reactive support.
Define a persistence.xml file, note the provider class must be specified as the one in Hibernate Reactive.
Declare a Mutiny.SessionFactory bean.
Then inject it in your repository class.
I have created a complete example demos Hibernate Reactive + Spring.
Update: Till now Spring team has no plan to support it, if you are willing to taste other framework, check Quarkus and Micronaunt, both have seamless Hibernate Reactive support. Check my Quarkus Hibernate Reactive example and Micronaut Hibernate Reactive example.
According to quote from previous answer
One could implement a ReactiveCrudRepository using JPA or JDBC and delegating the work to a thread pool. This would provide an async API on the outside, but would still consume the resources for the Threads and block between independent data accesses, so only a small part of the benefits of the reactive approach would get realized.
James Ward claims it can be non-blocking. I mean I asked him:
yeah ok, but isn't ScalikeJDBC-Async doing exactly the same? just putting query invocation into another thread pool?
and he replied
No because ScalalikeJDBC-Async uses https://github.com/mauricio... which is actually a non-blocking (NIO) JDBCish database driver.
source
So you can be reactive by replacing hibernate + spring data with postgresql-async (should work with mysql).
you could try with quarkus framework and panache mongo hibernate reactive repositories. https://quarkus.io/guides/mongodb-panache .It is easy manage a reactive repository over mongoDB, It is later but hope helps.
I want to access a Neo4j DB with Java and wanted to know what the preferred way to do this is. I just want to write a quite simple data structure to the DB.
http://neo4j.com/developer/java/ gives following options:
JDBC
Hibernate OGM
Spring Data
Rest API via Unmanaged Extensions
I looked into accessing Neo4J with JDBC and Hibernate OGM. It seems that its not worth it to use for me. JDBC gives me some trouble. So should i go with the REST way or try to fix my JDBC problems?
The JDBC driver is really a wrapper around the REST interface (as of neo4j 2.3). There is a example application how to use it. Should suffice for very simple use.
Then there is neo4j-ogm (different from Hibernate OGM) - this is an object graph mapping library, similar to hibernate in ORM world. This has minimal external dependencies and is very easy to use - ideal for cases where you want to map couple of objects into graph.
Then there is the Spring Data Neo4j project, which since version 4 uses neo4j-ogm for mapping, but adds other Spring data features, like repositories, derived finder queries, transactions ...
I have a Spring, Spring Data, JPA/Hibernate application.
The legacy part of the application uses JdbcTemplate the new stuff uses spring-data/hibernate and everything is wrapped in a transaction.
Problem is when I modify an entity via hibernate and the legacy part of the system attempts to query something that's been modified I don't get the updated values with out having to explicitly "flush" the entity manager each time.
Is it possible execute the JdbcTemplate queries against hibernate's first-level cache?
What about trying this?
Edit: https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/orm/jpa/JpaTransactionManager.html
This transaction manager also supports direct DataSource access within a transaction (i.e. plain JDBC code working with the same DataSource). This allows for mixing services which access JPA and services which use plain JDBC (without being aware of JPA)! Application code needs to stick to the same simple Connection lookup pattern as with DataSourceTransactionManager (i.e. DataSourceUtils.getConnection(javax.sql.DataSource) or going through a TransactionAwareDataSourceProxy). Note that this requires a vendor-specific JpaDialect to be configured.