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‎CONTRIBUTING.rst‎

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@@ -62,6 +62,5 @@ Note: make changes to the source/content/pages/\*.rst files then execute a
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2. Sync your repo with the original repo::
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$ git checkout master
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$ git fetch upstream
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$ git merge upstream/master
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$ git merge upstream/gh-pages

‎about-author.html‎

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@@ -125,7 +125,7 @@ <h3 class="panel-head"><a href="/table-of-contents.html" style="color: #fff;">Ta
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<a href="/data.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Data</a>
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<a href="/databases.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Databases</a>
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<a href="/no-sql-datastore.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>NoSQL Data Stores</a>
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<a href="/object-relational-mappers-orms.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Object-relational Mappers</a>
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<a href="/object-relational-mappers-orms.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Object-relational Mappers (ORMs)</a>
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<a href="/application-programming-interfaces.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Application Programming Interfaces</a>
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<a href="/api-integration.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>API Integration</a>
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<a href="/api-creation.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>API Creation</a>

‎all.html‎

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@@ -3101,15 +3101,21 @@ <h3>Key-value pair data stores</h3>
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</ul>
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<h3>Key-value pair resources</h3>
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<ul>
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<li>
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<p><a href="http://dba.stackexchange.com/questions/607/what-is-a-key-value-store-database">What is a key-value store database?</a>
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is a Stack Overflow Q&amp;A that straight on answers this subject.</p>
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</li>
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<li><a href="http://dba.stackexchange.com/questions/607/what-is-a-key-value-store-database">What is a key-value store database?</a>
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is a Stack Overflow Q&amp;A that straight on answers this subject.</li>
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</ul>
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<h3>Redis resources</h3>
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<ul>
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<li>
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<p>"<a href="https://www.digitalocean.com/community/tutorials/how-to-install-and-use-redis">How To Install and Use Redis</a>"
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is a guide for getting up with the extremely useful in-memory data store.</p>
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</li>
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<li>
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<p><a href="http://degizmo.com/2010/03/22/getting-started-redis-and-python/">Getting started with Redis and Python</a>
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is a walkthrough for installing and playing around with the basics of
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Redis.</p>
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</li>
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<li>
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<p>This video on
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<a href="https://www.youtube.com/watch?v=rP9EKvWt0zo">Scaling Redis at Twitter</a> is
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a detailed look behind the scenes with a massive Redis deployment.</p>
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<h2>Why are ORMs useful?</h2>
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<p>ORMs provide a high-level abstraction upon a
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<a href="/databases.html">relational database</a> that allows a developer to write
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Python code instead of SQL to create, read, update and delete data in
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their database. Developers can use the programming language they are
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comfortable with, in our case Python, to work with data and not have to
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write SQL statements or stored procedures.</p>
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<p>However, Python ORM libraries are not required for accessing relational
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databases. In fact, the low-level access is typically provided by another
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library, such as <a href="http://initd.org/psycopg/">psycopg</a> (for PostgreSQL)
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or <a href="https://pypi.python.org/pypi/MySQL-python/1.2.5">MySQL-python</a> (for
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MySQL).</p>
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<p>Developers can also use ORMs without a web framework, such as when
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creating a data analysis tool or a batch script without a user interface.</p>
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Python code instead of SQL to create, read, update and delete data and
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schemas in their database. Developers can use the programming language they
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are comfortable with to work with a database instead of writing SQL
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statements or stored procedures.</p>
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<p>For example, without an ORM a developer would write the following SQL
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statement to retrieve every row in the USERS table where the
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<code>zip_code</code> column is 94107:</p>
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<div class="highlight"><pre>SELECT * FROM USERS WHERE zip_code=94107;
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</pre></div>
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<p>The equivalent Django ORM query would instead look like the following Python
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code:</p>
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<div class="highlight"><pre># obtain everyone in the 94107 zip code and assign to users variable
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users = Users.objects.filter(zip_code=94107)
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</pre></div>
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<p>The ability to write Python code instead of SQL can speed up web application
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development, especially at the beginning of a project. The potential
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development speed boost comes from not having to switch from Python code
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into writing declarative paradigm SQL statements. While some software
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developers may not mind switching back and forth between languages, it's
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typically easier to knock out a prototype or start a web application using
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a single programming language.</p>
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<p>ORMs also make it theoretically possible to switch an application between
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various relational databases. For example, a developer could use SQLite for
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local development and MySQL in production. A production application could
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be switched from MySQL to PostgreSQL with minimal code modifications.</p>
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<p>In reality however, it's best to use the same database for local development
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as is used in production. Otherwise unexpected errors could hit in production
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that were not seen in a local development environment. Also, it's rare that
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a project would switch from one database in production to another one unless
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there was a pressing reason.</p>
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<div class="well see-also">
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While you're learning about ORMs you should also read up on
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<a href="/deployment.html">deployment</a> and check out the
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<a href="/application-dependencies.html">application dependencies</a> page.
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</div>
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<h2>Do I have to use an ORM for my web application?</h2>
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<p>Python ORM libraries are not required for accessing relational
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databases. In fact, the low-level access is typically provided by another
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library called a <em>database connector</em>, such as
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<a href="http://initd.org/psycopg/">psycopg</a> (for PostgreSQL)
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or <a href="https://pypi.python.org/pypi/MySQL-python/1.2.5">MySQL-python</a> (for
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MySQL). Take a look at the table below which shows how ORMs can work with
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different web frameworks and connectors and relational databases.</p>
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<p><img src="theme/img/orm-examples.png" width="100%" alt="Examples of how varying Python ORMs can work with different connectors and backends." class="technical-diagram" /></p>
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<p>The above table shows for example that SQLAlchemy can work with varying
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web frameworks and database connectors. Developers can also use ORMs without
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a web framework, such as when creating a data analysis tool or a batch
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script without a user interface.</p>
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<h2>What are the downsides of using an ORM?</h2>
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<p>There are numerous downsides of ORMs, including</p>
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<ol>
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<li>impedance mismatch</li>
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<li>difficulty writing complex queries</li>
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<li>potential for reduced performance</li>
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<li>shifting complexity into the application from the database layer</li>
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<li>Impedance mismatch</li>
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<li>Potential for reduced performance</li>
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<li>Shifting complexity from the database into the application code</li>
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</ol>
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<h2>Django's ORM</h2>
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<p>The <a href="/django.html">Django</a> web framework comes with its own built-in
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object-relational mapping module, generally referred to as "the Django ORM".</p>
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<h3>Impedance mismatch</h3>
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<p>The phrase "impedance mismatch" is commonly used in conjunction with ORMs.
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Impedance mismatch is a catch-all term for the difficulties that occur when
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moving data between relational tables and application objects. The gist
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is that the way a developer uses objects is different from how data is
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stored and joined in relational tables.</p>
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<p><a href="http://www.agiledata.org/essays/impedanceMismatch.html">This article on ORM impedance mismatch</a>
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does a solid job of explaing what the concept is at a high level and
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provides diagrams to visualize why the problem occurs.</p>
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<h3>Potential for reduced performance</h3>
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<p>One of the concerns that's associated with any higher-level abstraction or
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framework is potential for reduced performance. With ORMs, the performance
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hit comes from the translation of application code into a corresponding SQL
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statement which may not be tuned properly.</p>
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<p>ORMs are also often easy to try but difficult to master. For example, a
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beginner using Django might not know about the
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<a href="https://docs.djangoproject.com/en/1.8/ref/models/querysets/#select-related"><code>select_related()</code> function</a>
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and how it can improve some queries' foreign key relationship performance.
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There are dozens of performance tips and tricks for every ORM. It's possible
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that investing time in learning those quirks may be better spent just
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learning SQL and how to write stored procedures.</p>
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<p>There's a lot of hand-waving "may or may not" and "potential for" in this
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section. In large projects ORMs are good enough for roughly 80-90% of use
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cases but in 10-20% of a project's database interactions there can be
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major performance improvements by having a knowledgeable database
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adminstrator write tuned SQL statements to replace the ORM's generated
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SQL code.</p>
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<h3>Shifting complexity from the database into the app code</h3>
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<p>The code for working with an application's data has to live somewhere. Before
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ORMs were common, database stored procedures were used to encapsulate the
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database logic. With an ORM, the data manipulation code instead lives within
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the application's Python codebase. The addition of data handling logic in the
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codebase generally isn't an issue with a sound application design, but it does
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increase the total amount of Python code instead of splitting code between
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the application and the database stored procedures.</p>
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<h2>Python ORM Implementations</h2>
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<p>There are numerous ORM implementations written in Python, including</p>
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<ol>
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<li><a href="https://docs.djangoproject.com/en/1.8/topics/db/">The Django ORM</a></li>
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<li><a href="http://www.sqlalchemy.org/">SQLAlchemy</a></li>
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<li><a href="https://peewee.readthedocs.org/en/latest/">Peewee</a></li>
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<li><a href="http://ponyorm.com/">PonyORM</a></li>
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<li><a href="http://sqlobject.org/">SQLObject</a></li>
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</ol>
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<p>There are other ORMs, such as Canonical's
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<a href="https://storm.canonical.com/">Storm</a>, but most of them do not appear to
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currently be under active development. Learn more about the major active
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ORMs below.</p>
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<h3>Django's ORM</h3>
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<p>The <a href="/django.html">Django</a> web framework comes with
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its own built-in object-relational mapping module, generally referred to
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as "the Django ORM" or "Django's ORM".</p>
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<p><a href="https://docs.djangoproject.com/en/dev/topics/db/">Django's ORM</a> works well
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for simple and medium-complexity database operations. However, there are often
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complaints that the ORM makes complex queries much more complicated than
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replacing the default ORM with SQLAlchemy is currently a hack workaround. Note
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though that some of the Django core committers believe it is only a matter of
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time before the default ORM is replaced with SQLAlchemy. It will be a large
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effort to get that working though so it's likely to come in Django 1.9 or
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later.</p>
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effort to get that working though so it's likely to come in
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<a href="https://github.com/makaimc/fullstackpython.com/issues/48">Django 1.9 or later</a>.</p>
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<p>Since the majority of Django projects are tied to the default ORM, it's best to
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read up on advanced use cases and tools for doing your best work within the
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existing framework.</p>
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<h2>SQLAlchemy</h2>
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<p><a href="http://www.sqlalchemy.org/">SQLAlchemy</a> is currently the most respected
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Python ORM because it typically get the abstraction level "just right" and
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seems to make complex database queries easier to write than the Django ORM
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in most cases. SQLAlchemy is typically used with Flask as the database ORM
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via the <a href="https://pythonhosted.org/Flask-SQLAlchemy/">Flask-SQLAlchemy</a>
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<h3>SQLAlchemy</h3>
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<p><a href="http://www.sqlalchemy.org/">SQLAlchemy</a> is a well-regarded
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Python ORM because it gets the abstraction level "just right" and
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seems to make complex database queries easier to write than the Django
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ORM in most cases. SQLAlchemy is typically used with Flask as the database
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ORM via the <a href="https://pythonhosted.org/Flask-SQLAlchemy/">Flask-SQLAlchemy</a>
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extension.</p>
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<h2>Peewee</h2>
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<p><a href="https://peewee.readthedocs.org/en/latest/">Peewee</a> is another Python ORM
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<h3>Peewee</h3>
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<p><a href="https://peewee.readthedocs.org/en/latest/">Peewee</a> is a Python ORM
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written to be
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<a href="http://charlesleifer.com/blog/the-case-for-peewee-small-hackable-and-fun/">simpler, smaller and more hackable</a>
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"<a href="http://charlesleifer.com/blog/the-case-for-peewee-small-hackable-and-fun/">simpler, smaller and more hackable</a>"
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than SQLAlchemy. The analogy used by the core Peewee author is that Peewee
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is to SQLAlchemy as SQLite is to PostgreSQL. An ORM does not have to work
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for every exhaustive use case in order to be useful.</p>
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<h3>Pony</h3>
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<p><a href="http://ponyorm.com/">Pony ORM</a> is another Python ORM with a slight twist in
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its licensing model. The project is multi-licensed. Pony is free for use
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on open source projects but has a
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<a href="http://ponyorm.com/license-and-pricing.html">commercial license</a> that
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is required for commercial projects. The license is a one-time payment
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and does not necessitate a recurring fee.</p>
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<h3>SQLObject</h3>
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<p><a href="http://sqlobject.org/">SQLObject</a> is an ORM that has been under active
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open source development since
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<a href="http://sqlobject.org/News1.html#sqlobject-0-5">before 2003</a>.</p>
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<h2>Schema migrations</h2>
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<p>Schema migrations, for example when you need to add a new column to an
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existing table in your database, are not technically part of ORMs. However,
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<h3>General ORM resources</h3>
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<ul>
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<li>
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<p>This article does a solid job of explaing what
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<a href="http://www.agiledata.org/essays/impedanceMismatch.html">ORM impedance mismatch</a>
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is at a high level and provides diagrams to visualize why the problem
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occurs. There's also a detailed overview of <a href="http://www.agiledata.org/essays/mappingObjects.html">what ORMs are</a>
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<p>There's also a detailed overview of <a href="http://www.agiledata.org/essays/mappingObjects.html">what ORMs are</a>
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on another page of the website.</p>
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</li>
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<li>
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in an essay about how ORMs are often misused but that they do provide
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benefits to developers.</p>
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</li>
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<li>
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<p>If you're confused about the difference between a connector, such as
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MySQL-python and an ORM like SQLAlchemy, read this
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<a href="http://stackoverflow.com/questions/2550292/purpose-of-sqlalchemy-over-mysqldb">StackOverflow answer</a>
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on the topic.</p>
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</li>
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</ul>
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<h3>Django ORM resources</h3>
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<a href="https://peewee.readthedocs.org/en/latest/">Peewee ORM</a> instead of
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SQLAlchemy for the blog back end.</p>
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</li>
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</ul>
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<h3>Pony ORM resources</h3>
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<ul>
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<li>
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<p><a href="http://jakeaustwick.me/why-you-should-give-ponyorm-a-chance/">Why you should give Pony ORM a chance</a>
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explains some of the benefits of Pony ORM that make it worth trying out.</p>
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</li>
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<li>
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<p><a href="http://www.blog.pythonlibrary.org/2014/07/21/python-101-an-intro-to-pony-orm/">An intro to Pony ORM</a>
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shows the basics of how to use the library, such as creating databases
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and manipulating data.</p>
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</li>
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<li>
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<p>The Pony ORM author explains on a Stack Overflow answer
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<a href="http://stackoverflow.com/questions/16115713/how-pony-orm-does-its-tricks">how Pony ORM works behind the scenes</a>.
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Worth a read whether or not you're using the ORM just to find out how
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some of the magic coding works.</p>
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</li>
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</ul>
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<h3>SQLObject resources</h3>
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<ul>
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<li>
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<p>This post on
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<a href="http://www.andypatterns.com/index.php/blog/object_relational_mapping_pattern_-_using_sqlobj/">Object-Relational Mapping with SQLObject</a>
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explains the concept behind ORMs and shows the Python code for how they
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can be used.</p>
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</li>
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<li>
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<p>Ian Bicking presented on SQLObject back in 2004 with a talk on
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<a href="http://www.ianbicking.org/docs/sqlobject-presentation/sqlobject-and-database-programming.html">SQLObject and Database Programming in Python</a>.</p>
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</li>
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</ul>
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<h1>Application Programming Interfaces</h1>
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<p>Application programming interfaces (APIs) provide machine-readable
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<h2>2015</h2>
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<h3>June</h3>
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<ul>
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<li>Nice little update to the <a href="/object-relational-mappers-orms.html">ORMs page</a>
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with a diagram showing that different ORMs can work with varying
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web frameworks and backends.</li>
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<li>Added a new section just for Nginx resources and Removed broken links on
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the <a href="/web-servers.html">web servers</a> page.</li>
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<li>Added a new page on Python

‎api-creation.html‎

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<a href="/databases.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Databases</a>
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<a href="/no-sql-datastore.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>NoSQL Data Stores</a>
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<a href="/object-relational-mappers-orms.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Object-relational Mappers</a>
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<a href="/object-relational-mappers-orms.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Object-relational Mappers (ORMs)</a>
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<a href="/application-programming-interfaces.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Application Programming Interfaces</a>
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<a href="/api-integration.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>API Integration</a>
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<a href="/api-creation.html" class="list-group-item smaller-item active" style='font-family: "Helvetica Neue",sans-serif;'>API Creation</a>

‎api-integration.html‎

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<a href="/object-relational-mappers-orms.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Object-relational Mappers</a>
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<a href="/object-relational-mappers-orms.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Object-relational Mappers (ORMs)</a>
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<a href="/application-programming-interfaces.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>Application Programming Interfaces</a>
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<a href="/api-creation.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>API Creation</a>

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