Someone suggested I use an ORM for a project that I'm designing, but I'm having trouble finding information on what it is or how it works.
Can anyone give me a brief explanation of what an ORM is and how it works and how I should get started using one?
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An ORM (Object Relational Mapper) is a piece/layer of software that helps map your code Objects to your database.
Some handle more aspects than others...but the purpose is to take some of the weight of the Data Layer off of the developer's shoulders.
Here's a brief clip from Martin Fowler (Data Mapper):
Patterns of Enterprise Application Architecture Data Mappers
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".
An ORM library is a completely ordinary library written in your language of choice that encapsulates the code needed to manipulate the data, so you don't use SQL anymore; you interact directly with an object in the same language you're using.
For example, here is a completely imaginary case with a pseudo language:
You have a book class, you want to retrieve all the books of which the author is "Linus". Manually, you would do something like that:
book_list = new List();
sql = "SELECT book FROM library WHERE author = 'Linus'";
data = query(sql); // I over simplify ...
while (row = data.next())
{
book = new Book();
book.setAuthor(row.get('author');
book_list.add(book);
}
With an ORM library, it would look like this:
book_list = BookTable.query(author="Linus");
The mechanical part is taken care of automatically via the ORM library.
Using ORM saves a lot of time because:
Using an ORM library is more flexible because:
But ORM can be a pain:
for
loop.Well, use one. Whichever ORM library you choose, they all use the same principles. There are a lot of ORM libraries around here:
If you want to try an ORM library in Web programming, you'd be better off using an entire framework stack like:
Do not try to write your own ORM, unless you are trying to learn something. This is a gigantic piece of work, and the old ones took a lot of time and work before they became reliable.
Like all acronyms it's ambiguous, but I assume they mean object-relational mapper -- a way to cover your eyes and make believe there's no SQL underneath, but rather it's all objects;-). Not really true, of course, and not without problems -- the always colorful Jeff Atwood has described ORM as the Vietnam of CS;-). But, if you know little or no SQL, and have a pretty simple / small-scale problem, they can save you time!-)
Can anyone give me a brief explanation...
Sure.
ORM stands for "Object to Relational Mapping" where
The Object part is the one you use with your programming language ( python in this case )
The Relational part is a Relational Database Manager System ( A database that is ) there are other types of databases but the most popular is relational ( you know tables, columns, pk fk etc eg Oracle MySQL, MS-SQL )
And finally the Mapping part is where you do a bridge between your objects and your tables.
In applications where you don't use a ORM framework you do this by hand. Using an ORM framework would allow you do reduce the boilerplate needed to create the solution.
So let's say you have this object.
class Employee:
def __init__( self, name ):
self.__name = name
def getName( self ):
return self.__name
#etc.
and the table
create table employee(
name varcar(10),
-- etc
)
Using an ORM framework would allow you to map that object with a db record automagically and write something like:
emp = Employee("Ryan")
orm.save( emp )
And have the employee inserted into the DB.
Oops it was not that brief but I hope it is simple enough to catch other articles you read.
Object Model is concerned with the following three concepts Data Abstraction Encapsulation Inheritance The relational model used the basic concept of a relation or table. Object-relational mapping (OR mapping) products integrate object programming language capabilities with relational databases.
Source: Stackoverflow.com