After you failed to convince the customer this is a really bad idea, you reluctantly implement the change. Indirection #Ĭontinuing with our save_user-example, at some point one of your software's customers wants to store the user data in a file rather than in a database. Level of indirection software#Software layers are a great way to organize code but it requires vision and discipline to introduce and maintain them. developers didn't value maintaining an architecture layer for a particular system. developers had to bypass a layer because the layer below it is too slow or difficult to changeģ. layers are poorly defined in code and groupmind, where something belongs has become vague Ģ. In practice this is often a point of discussion or ignored completely. To maintain a layered architecture developers should avoid leaking responsibilities from one layer to the next. Data Layer - this contains any data mapping (ORM) and data sources (database, file system etc).Domain Layer - contains your business rules and logic.This might be generated HTML, a JSON API, RMI or any other type of external interface. Presentation Layer - anything that provides the interaction of your software system to a client/consumer. A popular high-level architecture layering model was described by Martin Fowler: It is not uncommon for a codebase to be completely separated in layers where each piece of code is part of a dedicated software layer. Return query ( "INSERT INTO users (c1, c2) VALUES(%s, %s)", (name, email ) ) Return insert_user (name, email ) # user_db.py Example solution #Īfter moving and cleaning up your database handling logic within a separate user_db module your save_user function now looks like this: # user.py These files will act as a database access layer all communication to the database is done strictly through this software module and access to the database anywhere else is avoided. Solution #Ĭoncentrate all database logic in a dedicated set of files, separate from the rest of the code. Changes to database structure and logic requires updating multiple parts of the codebase which is time-consuming and error-prone. Your code contains a lot of repetitive database code. On top of that the functions update_user(user_id) and delete_user(user_id) which contain a very similar sets of code. execute ( "INSERT INTO users (name, email) VALUES(%s, %s)", (name, email ) )ĭef update_user (user_id, name, email ) :Ĭode was added to fetch the generated user_id that the database automatically generated and the error handling was improved. The save_user function now looks like this: # user.pyĬur. Layering your codebase tends to become more useful when software starts to grow, so let's assume our example has undergone some changes over time. execute ( "INSERT INTO users (c1, c2) VALUES(%s, %s)", (name, email ) ) A basic implementation could look like this: # user.pyĬonn = database_lib. Let's assume you're implementing a function that validates and stores a user's name and email address in a database. I'll illustrate the topics by using a Python example. There are many aspects to this, so I'll split this article in three sections: Recently a developer asked me what was meant with the following quote:Īll problems in computer science can be solved by another level of indirection, except for the problem of too many layers of indirection. Layers of Indirection Control flow Python Layering Indirection
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