Object-Relational Mapping (ORM) is a technique that lets you query and manipulate data from a database using an object-oriented paradigm. When talking about ORM, most people are referring to a library that implements the Object-Relational Mapping technique, hence the …

2013年2月19日 · Well, ORM stands for... actually, I'll let this answer explain: Object-Relational Mapping (ORM) is a technique that lets you query and manipulate data from a database using an object-oriented paradigm. When talking about ORM, most people are referring to a library that implements the Object-Relational Mapping technique, hence the phrase "an ORM".

ORM (Object Relational Mapper) Object Relational Mapping (ORM) is a technique (Design Pattern) of accessing a relational database from an object-oriented language. If you have used any kind of frameworks like Symfony (if you come from PHP background)/Hibernate (Java), then your familiar with these. Its nothing but Entities.

SQLAlchemy is more full-featured and powerful (uses the DataMapper pattern). Django ORM has a cleaner syntax and is easier to write for (ActiveRecord pattern). I don't know about performance differences. SQLAlchemy also has a declarative layer that hides some complexity and gives it a ActiveRecord-style syntax more similar to the Django ORM.

There are definitely some optimisation issues that you will encounter but the abstraction of the database interface probably over-rides these downsides. You mention that the ORM sometimes uses many sql statements where it could use only one. You may want to look at "eager loading", if this is supported by your ORM.

If it is an OLAP database (e.g. static, read-only data used for reporting/analytics, etc.) then implementing an ORM framework is not appropriate. Instead, using the database's native data access functionality such as stored procedures would be preferable.

2008年9月20日 · MicroMVC has a 13 KB ORM that only relies on a 8 KB database class. It also returns all results as ORM objects themselves and uses late static binding to avoid embedding information about the current object's table and meta data into each object. This results in the cheapest ORM overhead there is. It works with MySQL, PostgreSQL, and SQLite.

SQLAlchemy's ORM is meant to be used together with the SQL layer, not hide it. But you do have to keep one or two things in mind when using the ORM and plain SQL in the same transaction. Basically, from one side, ORM data modifications will only hit the database when you flush the changes from your session.

The most important reason to use an ORM is so that you can have a rich, object oriented business model and still be able to store it and write effective queries quickly against a relational database. From my viewpoint, I don't see any real advantages that a good ORM gives you when compared with other generated DAL's other than the advanced ...

2010年4月23日 · You can even go straight for an OO database. As a sidenote: ORM also serves the need to keep on supporting existing data stored in relational databases while the code (business model) has been rewritten to an OO style. If your project starts from scratch, there is no need to opt for a relational database per se.