ORM: Problem: Impedance Mismatch (i.e., different languages for data and programming, need casting between types, makes analysis difficult) Solution: Object-Relation-Mapping middleware (provide an persistence abstraction for objects, and takes care of transformation from/to the DB world)"Everyone who is somebody has one! Either standard (e.g., hibernate) or ad-hoc." The idea is to provide:- pre-canned mapping between OO classes/fields and table/columns- manually defined mappings- provides object persistency without looking at the DB Good: - abstraction - ease of debug Bad: - performance Example: Hibernate Example of Hibernate Mapping <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" Application dialogs- Swing- SWT- Web applicationApplication logicClass Order Class CustomerInstance of Customer classHibernateRow of Customer tableDatabaseTable Order-id-number-customer_idTable Customer-id-firstname-lastname-dateImage by MIT OpenCourseWare.------------------------------------------------------------------------------------------"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" ><hibernate-mapping><class name="de.laliluna.example.Honey" table="honey"> <id name="id" column="id" > <generator class="increment"/> </id> <property name="name" column="fooname" /> <property name="taste" column="bartaste" /> </class> </hibernate-mapping> Example of Hibernate Usage (many details are hidden) Honey honey = new Honey(); honey.setName("forest honey"); honey.setTaste("very sweet"); … tx = session.beginTransaction(); session.save(honey); tx.commit(); … tx = session.beginTransaction(); session.update(honey); tx.commit(); … tx = session.beginTransaction(); List honeys = session.createQuery("select h from Honey as h").list(); tx.commit(); Next we talk about DriadLINQ… it provides similar features but adds much more in particular:- LINQ language integration- Batch-oriented - Cluster-oriented - More than SQLMIT OpenCourseWare http://ocw.mit.edu 6.830 / 6.814 Database Systems Fall 2010 For information about citing these materials or our Terms of Use, visit:
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