I just noticed that a part of code I worked on saves the same entity twice.
I tried several tricks, like flush() and Transaction REQUIRES_NEW but nothing does it.
But I can see while debugging that after calling persist(entity), I get an ID (IDENTITY) for that entity... but just a bit later in the code if I look at the variables I'll see the same entity with a different ID and two itenties with those IDs in the Table.
This is using Java EE 6 with Glassfish 3.0.1
What JPA provider are you using? and what version?
Enable logging (on finest) and include the log of what occurs.
If using EclipseLink to enable logging see,
http://wiki.eclipse.org/EclipseLink/Examples/JPA/Logging
What value is assigned to your object's id, check to ensure it is > 0.
Also ensure that you table in the database was generated with an IDENTITY column.
What database are you using?
Try using TABLE sequencing to see if it has to do with IDENTITY sequencing.
Also include the source code for you class.
Related
I'm playing around with spring-data-jdbc and discovered a problem, with I can't solve using Google.
No matter what I try to do, I just can't push a trivial object into the database (Bean1.java:25):
carRepository.save(new Car(2L, "BMW", "5"));
Both, without one and with a TransactionManager +#Transactional the database (apparently) does not commit the record.
The code is based on a Postgres database, but you might also simply use a H2 below and get the same result.
Here is the (minimalistic) source code:
https://github.com/bitmagier/spring-data-jdbc-sandbox/tree/stackoverflow-question
Can somebody tell me, why the car is not inserted into the database?
This is not related to transactions not working.
Instead, it's about Spring Data JDBC considering your instance an existing instance that needs updating (instead of inserting).
You can verify this is the problem by activating logging for org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate. You should see an update but no insert.
By default, Spring Data JDBC considers an entity as new when it has an id of an object type and a value of null or of a primitive type (e.g. int or long) and a value of 0.
If your entity has an attribute with #Version annotation that attribute will be used to determine if the instance is a new one.
You have the following options in order to make it work:
Set the id to null and configure your database schema so that it will automatically create a new value on insert. After the save your entity instance will contain the generated value from the database.
Note: Spring Data JDBC will set the id even if it is final in your entity.
Leave the id null and set it in a Before-Convert listener to the desired value.
Let your entity implement Persistable. This allows you to control when an entity is considered new. You'll probably need a listener as well so you can let the entity know it is not new any longer.
Beginning with version 1.1 of Spring Data JDBC you'll also be able to use a JdbcAggregateTemplate to do a direct insert, without inspecting the id, see https://jira.spring.io/browse/DATAJDBC-282. Of course, you can do that in a custom method of your repository, as is done in this example: https://github.com/spring-projects/spring-data-examples/pull/441
We're using a very basic JPA implementation that should create tables consistently from our models.
I believe we're using EclipseLink or TopLink (whichever one is default with the latest Netbeans/Glassfish). The problem is, the tables are created with inconsistent capitaliztion and with the columns out of order. For me, It creates the "User" table as "user", and for other members of my team it creates "USER".
I've tried using the #Table annotation (#Table(name="USer")), but it doesn't work.
How do we get EclipseLink to generate consistent table names? Frankly this seems like a rather amateurish mistake for a framework like this.
Sub-question : the reason this is a problem is because EclipseLink by default has no default way of managing schema/data migrations, as far as I know of. The way we're handling it is by writing a bunch of INSERT INTO's to bootstrap the objects we need in our database, and drop-and-recreating the tables every time the schema changes. I know this is not the best practice for propagating schema changes -- does anyone know how this is typically handled in a standard JPA implementation?
Thanks.
By default EclipseLink uses all upper case for the table name, the class User would be USER.
If you specify an #Table annotation with name="USer", then the table will be created as "USer".
Perhaps you are using your own scripts to create the tables, or you database is changing the case based on the OS or its own settings. What database are you using?
If you enable logging in EclipseLink, it will show the exact DDL that it is executing (if it is executing DDL).
In EclipseLink 2.4 there is also a "create-or-extend-tables" DDL generation option to alter existing tables.
We never found any good answer for this. Luckily, we found a workaround for the ways we were using to update the table, which didn't care about capitalization.
Trying to persist an entity which contains a member variable that is a reference to some other entity which is not under the current persistence context will not be possible, when this happens one needs to fetch the required entity and set it in the original entity in order to respect the relationship and be allowed to persist it.
When I need to accomplish this I usually make use of the EntityManager's find method, but that will hit the database and fetch the entire entity along with it's relationships that may not be annotated for lazy loading. I was happy to find out about getReference, which suposedly won't hit the database but return a proxy representation where only the primary key is available and that is really all that is required for this type of situation.
Unfortunately after some debugging I find myself being able to view all the information about the getReference'd entity and not just the primary key when I "inspect" it via Eclipse debug mode.
Am I missing something? Am I being deceived by the debug mode? Could it be fetching the information like a getter method would when used on the proxy reference?
Thanks in advance
Whe you inspect it using the Eclipse debugger, the debugger initializes the proxy. Just turn on SQL logging, execute the em.getReference() method, and verify that no select statement has been executed by your JPA engine.
As the title says, how do I view the SQL generated by Entity Framework from within my code? I'm running into an error where the EF is crashing because a field is generated by the database (a DateTime field), and I thought I set it to know that the store is generating it via StoreGeneratedPattern, but it's still crashing, so I would like to see what exactly it's trying to push up to the database.
P.S. I've only been using EF for about an hour now... Switching from L2S.
Since you don't have Sql Profiler, your best choice would be LINQPad. You can use your existing assembly.
Click Add connection -> Use a typed data context from your own assembly -> Entity framework and select your dll.
You can write queries directly against your model (or copy-paste from your code). Select the SQL 'tab' under the query window to view the generated SQL code.
You can use the Entity Framework Profiler (EFProf). It's not free, but there's a 30-day trial available. It does a lot more neat stuff besides showing you the SQL statements.
Generally, you should always use SQL Profiler to see the SQL statements that being submitted by EF into your database.
Also, I think you misunderstood about what StoreGeneratedPattern is. If you look at its possible values inside the model, you'll see that it has identity meaning that the value will be generated (by the database) when the row is inserted and will not otherwise change. The other options are Computed, which specifies that the value will be generated on inserts and updates, and None, which is the default.
So EF will not generate that DateTime field on the fly for you, you need to manually create it and then update your model from database so that EF will generate appropriate metadata to work with it at runtime.
The free AnjLab Sql Profiler will work if real SQL Profiler is not available because you're using SQL Server Express: http://anjlab.com/en/projects/opensource/sqlprofiler. It's not quite as nice as the real thing but it gets the job done well enough.
One solution would be to capture the network traffic and have a look at the data on that level. Microsoft Network Monitor does a good job of this.
Of course, that only works if you're using a separate DB server, and the connection is not encrypted.
A have a JPA entity that has timestamp field and is distinguished by a complex identifier field. What I need is to update timestamp in an entity that has already been stored, otherwise create and store new entity with the current timestamp.
As it turns out the task is not as simple as it seems from the first sight. The problem is that in concurrent environment I get nasty "Unique index or primary key violation" exception. Here's my code:
// Load existing entity, if any.
Entity e = entityManager.find(Entity.class, id);
if (e == null) {
// Could not find entity with the specified id in the database, so create new one.
e = entityManager.merge(new Entity(id));
}
// Set current time...
e.setTimestamp(new Date());
// ...and finally save entity.
entityManager.flush();
Please note that in this example entity identifier is not generated on insert, it is known in advance.
When two or more of threads run this block of code in parallel, they may simultaneously get null from entityManager.find(Entity.class, id) method call, so they will attempt to save two or more entities at the same time, with the same identifier resulting in error.
I think that there are few solutions to the problem.
Sure I could synchronize this code block with a global lock to prevent concurrent access to the database, but would it be the most efficient way?
Some databases support very handy MERGE statement that updates existing or creates new row if none exists. But I doubt that OpenJPA (JPA implementation of my choice) supports it.
Event if JPA does not support SQL MERGE, I can always fall back to plain old JDBC and do whatever I want with the database. But I don't want to leave comfortable API and mess with hairy JDBC+SQL combination.
There is a magic trick to fix it using standard JPA API only, but I don't know it yet.
Please help.
You are referring to the transaction isolation of JPA transactions. I.e. what is the behaviour of transactions when they access other transactions' resources.
According to this article:
READ_COMMITTED is the expected default Transaction Isolation level for using [..] EJB3 JPA
This means that - yes, you will have problems with the above code.
But JPA doesn't support custom isolation levels.
This thread discusses the topic more extensively. Depending on whether you use Spring or EJB, I think you can make use of the proper transaction strategy.