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Re: [eclipselink-users] Questions about BLOB and XML support plus a few other questions
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Hi Carl,
1. Select for Update is supported in the JPA specification and through
EcipseLink query hints. Have a look at section 3.4.3 of the JPA 2.0
specification for the spec-based info. The following link provides
documentation about the query hint we use to allow pessimistic locking:
http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#Pessimistic_Lock
If you use the spec-based approach, they will be supported by other compliant
providers. Query hint support will be different depending on the provider.
2. I'm not sure what you mean by "streaming of Blobs". JPA supports mapping to
LOBs in the database. You can find information about mapping lobs in the JPA
2.0 Specification. The mapping annotation is documented in section 11.1.24. To
use this functionality, it is as simple as mapping a LOB in your Entity.
This is spec-based and compliant providers will support it. The only potential
issue is if a provider has not provided support for the particular database you
are using.
3. Here's some documentation about direct to XMLType mappings on Oracle.
http://wiki.eclipse.org/Configuring_a_Relational_Direct-to-XMLType_Mapping_(ELUG)
Unfortunately, support for other DBs will require some additional work on your part.
This is EclipseLink-specific.
4. Connection Pooling is supported, as are cached statements. The most common
way to use connection pooling is to simply attach to the connection pool
provided by your application server. In that case the management of cached
statements is up to the server.
I suspect all providers deal with external connection pooling. There may be
subtle differences, but in general, this is supported through the spec with JTA
persistence contexts.
If you do not have an external connection pool, EclipseLink provides it's own.
(EclipseLink only)
EclipseLink also provides a query caching feature that saves information about
compiled queries for later use. (EclispeLink only)
-Tom
Carl Roberts wrote:
Hello,
I am Developer at Oracle - IGBU and we have written an application with
custom JDBC DAO objects for each table and this has worked well until we
started adding more complex relationships between the tables and now I
am exploring using EcpliseLink as a solution to handle the table
relationships, however, before I switch to use EclipleLink, I have a few
questions:
1 - Can we do select for update queries against different databases to
avoid retrieving the same records in multiple threads? If so are there
any example documents that show this?
2 - Can we do streaming of Blobs? If so, are there any example documents
that show how to do this?
3 - Can we insert and retrieve into XML columns, meaning XMLType in
Oracle, and XML in DB2 or MSSQL? If so, are there any example documents
that show how to do this?
4 - Is connection pooling supported and how does that work with caching
of prepared statements? In other words, am I guaranteed to get a cached
prepared statement when I get a connection from the pool?
5 - For answers 1 - 4 above, if there are solutions, will they be
proprietary or will I be able to just use / write to the JPA API and can
then expect them to work with other providers.
I am looking for more than just on! e line answers, and preferably some
real documentation or example links that answer these questions so I can
do additional research to determine if switching is going to be feasible
for us.
Thank you in advance for any help that you can provide.
Joe
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