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Apache Empire-db

 1 year ago
source link: https://empire-db.apache.org/pages/home.html
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Apache Empire-db

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Full SQL Freedom for Java
Version 3.0.0 Released 2022/03/11
  • Apache Empire-db lets you utilize Relational-DBMS in Java without limitations, thus allowing to unleash the full power of the database-system.
  • Forget OR-Mapping, Entity Beans, Lazy vs Eager, Bytecode Proxies, TupleQuery and black box magic and reclaim your full SQL freedom.
  • No Annotation madness, No Mapping-File pain, No fancy stuff to represent your data model. Just simple old, plain old Java API.
  • Create even the most complex SQL in code in the simplest and most intuitive way, with "No Strings attached" (literally!)
  • Improve Compile-Time-Safety and code maintainability. Write DBMS independent code. Benefit from Identity-management and concurrency control. Perform DDL operations. Access Metadata. You name it…
  • Clever Object Model lets you customize and extend almost every aspect of its API by simple subclassing and overriding. No rocket science!
  • 100% Open-Source. 100% Free. Lightweight and straightforward.
  • Support for Oracle, SQLServer, PostgreSQL, MySQL, HsqlDB, Derby, H2 and more…

Natural selection

Here's a little appetizer showing a query of car model sales:

// create a command
DBCommand cmd = context.createCommand()
   .select  (BRAND.NAME, MODEL.SPECIFICATION, MODEL.BASE_PRICE)
   .select  (SALES.MODEL_ID.count(), SALES.PRICE.avg())
   .select  (SALES.PRICE.avg().minus(MODEL.BASE_PRICE.avg()).round(2).as("DIFFERENCE"))
   .join    (MODEL.WMI, BRAND.WMI)
   .joinLeft(MODEL.ID, SALES.MODEL_ID, SALES.YEAR.is(2021))  // only year 2021
   .where   (MODEL.ENGINE_TYPE.in(EngineType.P, EngineType.H, EngineType.E)) // Petrol, Hybrid, Electric
   .where   (MODEL.BASE_PRICE.isGreaterThan(30000))
   .groupBy (BRAND.NAME, MODEL.SPECIFICATION, MODEL.BASE_PRICE)
   .having  (SALES.MODEL_ID.count().isGreaterThan(5))   // more than 5 sales
   .orderBy (BRAND.NAME.desc(), MODEL.SPECIFICATION.asc());

// Return a list of Java beans (needs matching fields constructor or setter methods)
// This is just one of several options to obtain and process query results
List<QueryResult> list = context.getUtils().queryBeanList(cmd, QueryResult.class, null);
log.info("queryBeanList returned {} items", list.size());

SELECT t1.NAME, t2.SPECIFICATION, t2.BASE_PRICE
   , count(t5.MODEL_ID), avg(t5.PRICE)
   , round(avg(t5.PRICE)-avg(t2.BASE_PRICE),2) AS DIFFERENCE
FROM MODEL t2
     INNER JOIN BRAND t1 ON t1.WMI = t2.WMI
     LEFT JOIN SALES t5 ON t5.MODEL_ID = t2.ID AND t5.YEAR=2021
WHERE t2.ENGINE_TYPE IN ('P', 'H', 'E') AND t2.BASE_PRICE>30000
GROUP BY t1.NAME, t2.SPECIFICATION, t2.BASE_PRICE
HAVING count(t5.MODEL_ID)>5
ORDER BY t1.NAME DESC, t2.SPECIFICATION

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