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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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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:
With an ORM library, it would look like this:
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:
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.
Can anyone give me a brief explanation...
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.
Using an ORM framework would allow you to map that object with a db record automagically and write something like:
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.
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):
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!-)
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.

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What is ORM? Object-Relational Mapping Explained
use Illuminate\Database\Eloquent\Model;
* Get the phone record associated with the user.
* App\Phone is the class that represents the Phone object
* That class also extends Model like this one
return $this - > hasOne ( 'App\Phone' ) ;
hasOne('App\Phone');
}
}
use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;
class CreateFlightsTable extends Migration
Schema::create ( 'flights' , function ( Blueprint $table ) {
bigIncrements('id');
$table->string('name');
$table->string('airline');
$table->timestamps();
});
}

/**
* Reverse the migrations.
*
* @return void
*/
public function down()
{
Schema::drop('flights');
}
}
first_name = models. CharField ( max_length= 50 )
last_name = models. CharField ( max_length= 50 )
instrument = models. CharField ( max_length= 100 )
artist = models. ForeignKey ( Musician, on_delete=models.CASCADE )
name = models. CharField ( max_length= 100 )
release_date = models. DateField ()
num_stars = models. IntegerField ()
from django.db import models

class Musician(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
instrument = models.CharField(max_length=100)

class Album(models.Model):
artist = models.ForeignKey(Musician, on_delete=models.CASCADE)
name = models.CharField(max_length=100)
release_date = models.DateField()
num_stars = models.IntegerField()
public string UserName { get ; set ; }
public string EmailAddress { get ; set ; }
public class User
{
public int Id { get; set; }
public string UserName { get; set; }
public string EmailAddress { get; set; }
}

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If you write Object-Oriented Code , having a place to store your data is a must. In fact, the traditional way to go is to use a Relational Database . You can use Microsoft SQL, MySQL, or PostgreSQL, but in any case, you know the pain. You have to spend time mapping between tables and your classes, create methods to save in the database and read from it, and so on. Well, not anymore my friend. In this post, we will explain what is ORM (Object-Relational Mapping) , a solution that will solve all your pains.
If instead, you are searching for a free Relational Database, we can help you get started with MySQL. Here you find how to install MySQL on Windows and Linux , and here you have a great tutorial on MySQL queries .
ORM stands for Object-Relational Mapping , it is a programming technique that abstracts your code from the database behind it. In plain English, if you are using ORM and a MySQL database, you could switch to PostgreSQL at any time without changing your code. At all.
Note: ORM goes together with Database Abstraction Layer (DBAL). As we will see, ORM lets you use classes instead of database tables, and those classes implement DBAL to save you from writing queries.
This is because, with ORM, you never write queries to the database in your code. Instead, you only interact with objects of specific classes, that represent records in the database. Obviously, at some point, someone needs to make actual queries to the database. But that’s not you, it is the ORM class that does it for you, in a way that is completely transparent.
ORM is also about not reinventing the wheel . You can find open-source ORM libraries for literally any programming language. Typically, such libraries provide you with something like a “database object” superclass, and you create other classes inheriting from that. You will use your classes to represent your data.
You don’t even need to create tables in your database. Depending on the ORM library, this is taken care of simply by looking at object definitions, or with migrations (more on that later).
Examples make everything clearer. Imagine you want to create an e-commerce website. Among many other things, you need to consider that a customer may have multiple shipping addresses to receive products. Thus, you need to take care of that in your data structure.
You start by modeling a new class, Account , to hold all the data of your customers like email, password, and so forth. Then, you create another class, ShippingAddress , to hold information about one individual address. When you do that with ORM, ORM creates two tables in the database (e.g. account and shipping_address ) to map such objects.
Having the two objects is not enough. You need to define that the Account can have multiple ShippingAddress objects in it, so you simply define a property on it as an array of ShippingAddress . This is it, the code will take care of the relationship as well.
Now, depending on the programming language, you may do this in slightly different ways, but the core concept is always this one.
Unlike what you might expect, database migrations are not necessarily the transition from a database to another. Instead, they are the bread and butter of Object-Relational Mapping. Simply put a migration is an instruction to execute in the database to modify the database structure. A migration could create a new table, delete an existing one, or modify some fields or relationships.
You don’t write migrations using queries. Instead, you write them with the ORM syntax, and then ORM will create the queries for you in the proper way, depending on what database you are actually using.
Again, this varies from ORM library to ORM library, but the concept is always similar. You will have one file to define each migration, but each migration can contain multiple instructions. Furthermore, each migration must define two things: the up and the down . The up is what to do when implementing the migration, the down is what to do in case of rollback.
For example, a migration can create a table in its up part, and delete it in its down part. In this way, you can return back to the previous database configuration if needed.
Some ORMs go even further. They automatically build migrations for you by looking at the definition of your classes.
Now that we know what is ORM , we can get started with it. Below, some nice libraries to use ORM in various programming languages.
My favorite ORM in PHP is Eloquent, which comes packaged inside Laravel, a nice framework that helps you build nice applications. You can see Eloquent official documentation here . Below, an example of Eloquent code.
And below, an example of migration.
We took both examples from the official documentation linked above. Eloquent is a good choice, particularly if you are already using Laravel. More on Laravel? Check out our Laravel migration tutorial .
Of course, Eloquent is not the only way to go for PHP. There are many ORMs out there, but this post is about what is ORM , so there is no point covering them all here. Yet, we can recommend two other ORMs:
As always, do your own research to find out which is the best ORM to fit your project.
Django is a great python project that helps you to build a fully-fledged web application. Among its other features, it has an amazing ORM that can save you a lot of time. For example, with it, you don’t have to write migrations manually. Below, an example of its simplicity.
As you can see from the example, you directly define fields and relationships when defining the classes. In this case, the Album class references the Musician class (in the artist field). This example comes from the official Django documentation on models that you can find here .
Another great ORM for Python that is worth considering is SQLAlchemy. Unlike Django models, this comes as standalone, which makes it a great alternative for standalone projects. You can read more about it from the official website .
Just one remark: it is probably easier to start with Django models than with SQLAlchemy, as Django gives you more automation.
If you are using C#, one of your best bets when it comes to ORM is Dapper. This NuGet library allows you to define objects instead of making queries. You can read more about it in the GitHub Dapper project . Like in the previous cases, an example below.
If instead, you are a plain old Java Developer , you may want an ORM for that language. Java has been out there for a while, and you have many options, but probably the best way to go is Hibernate. Check out more in the official documentation .
Also there, you have to define classes and properties in them. Like any ORM, you will use that to represent your database structure.
In this post we saw what is ORM and, by extension, what is DBAL . In short, ORM is a programming technique where you write code, and that code gets translated into SQL queries for you. Many
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