I'm trying to create a JPA specification (criteria builder) to retrieve data from two separate tables (union of two tables). Any thought ?
The main purpose is to make it easy to add search filter and pagination when querying from the two tables.
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I'm considering using spring-data-jdbc for a project.
But i don't have any control over the DB-schema.
My domain model can be populated by the existing tables, but they differ in many ways.
Examples:
A specific aggregate in my model consists of nested Value-Objects. The corresponding table only features flat columns, so the nested Value-Objects would have to be mapped manually.
One the other hand, there are aggregates that don't have many nested Value-Objects, but the corresponding tables are organized according to a star-schema, so the values are distributed over many tables (instead of a single one).
I guess this prevents me from using many of the Quality-Of-Life features (like Query-Derivation and Mapping).
Do I actually get anything significant out of spring-data-jdbc in comparison to using a plain JdbcTemplate in this scenario?
The scenario you describe would make me tend towards plain JdbcTemplate.
But I would consider using the Aggregate approach Spring Data JDBC does:
Load complete aggregates
Reference between aggregates using ids, or something like an AggregateReference
And if you have an aggregate that actually can be mapped using Spring Data JDBC you can still do that.
I'm using Spring Data JPA to expose REST APIs. In my application, there are two types of tables available(current and archival) and structure of the current and archival tables are exactly similar and data will be moved for current table to archival table over the period of time for performance reasons. I'm having repository classes to retrieve the data from current and archival table separately and Pagination is also implemented for repositories.
Now I got a requirement to fetch the eligible records from both tables based on criteria and apply pagination at single shot. Is it possible with Spring Data JPA
You can keep the latest version in both tables and when you search for data you just do a regular search.
Another option would be to create a view over the two tables.
I also think Hibernate Envers was able to do that though I never tried it.
I am looking to read data from multiple tables (different database tables) and aggregate and create final result set. In my case, each query will return the List of object. I went through web many times, I found no link other than - Spring Batch How to read multiple table (queries) as Reader and write it as flat file write, but it returns only single object.
Is there any way if we can do this ? Any working sample example would help a lot.
Example -
One query gives List of Departments - from Oracle DB
One query gives List of Employee - from Postgres
Now I want to build Employee and Department relationship and send final object to processor to further lookup against MongoDB and send the final object to reader.
The question should rather be "how to join three tables from three different databases and write the result in a file". There is no built-in reader in Spring Batch that reads from multiple tables. You either need to create a custom reader, or decompose the problem at hand into tasks that can be implemented using Spring Batch tasklet/chunk-oriented steps.
I believe you can use the driving query pattern in a single chunk-oriented step. The reader reads employee items, then a processor enrich items with 1) department from postgres and 2) other info from mongo. This should work for small/medium datasets. If you have a lot of data, you can use partitioning to parallelize things and improve performance.
Another option if you want to avoid a query per item is to load all departments in a cache for example (I guess there should be less departments than employees) and enrich items from the cache rather than with individual queries to the db.
We are using SpringData and JPA in our project. Large data sets are to be retrived from the database. Is there any way we can 'Stream' the results from database. I could find solutions where stream is possible with Spring Data but we have to use '#Query' or 'Named Queries'. As per our requirement we have to create query predicates (where clause) dynamically. With '#Query' and 'NamedQueries', its not possible to create dynamic queries. Please share if you have any solution.(we require Streams + dynamic queries)
I need to search over multiple tables, getting only one resultset, but these tables don't have any relationship.
Can I do it with Solr?
Maybe Solr's aliases might fit your needs.
Create your alias with :
http://[solr.host:port]/solr/admin/collections?action=CREATEALIAS&name=testalias&collections=[collection1],[collection2]
and then query as usual as if "testalias" was one collection. For example:
http://[solr.host:port]/solr/testalias/select?q=:&rows=100&wt=json&indent=true
This query will return all the data from both collections.