Code Smell 142 — Queries in Constructors

Code Smell 142 — Queries in ConstructorsAccessing a database in domain objects is a code smell. Doing it in a constructor is a double smellTL;DR: Constructors should construct (and probably initialize) objects.ProblemsCouplingSide EffectsSolutionsDecou…


This content originally appeared on Level Up Coding - Medium and was authored by Maximiliano Contieri

Code Smell 142 — Queries in Constructors

Accessing a database in domain objects is a code smell. Doing it in a constructor is a double smell

TL;DR: Constructors should construct (and probably initialize) objects.

Problems

Solutions

  1. Decouple essential business logic from accidental persistence
  2. On persistence classes run queries in functions other than constructors/destructors

Context

On legacy code, the database is not correctly separated from business objects.

Constructors should never have side effects.

According to the single responsibility principle, they should only build valid objects

Sample Code

Wrong

public class Person {
  int childrenCount; 
  public Person(int id) {
    childrenCount = database.sqlCall("SELECT COUNT(CHILDREN) FROM PERSON WHERE ID = " . id); 
  }
}

Right

public class Person {
  int childrenCount; 
  // Create a class constructor for the Main class
  public Person(int id, int childrenCount) {
    childrenCount = childrenCount; 
    // We can assign the number in the constructor
    // Accidental Database is decoupled
    // We can test the object
  }
}

Detection

[X] Semi-Automatic

Our linters can find SQL patterns on constructors and warn us.

Tags

  • Coupling

Conclusion

Separation of concerns is key and coupling is our main enemy when designing robust software.

More Info

Credits

Photo by Callum Hill on Unsplash

My belief is still, if you get the data structures and their invariants right, most of the code will kind of write itself.

Peter Deustch

Software Engineering Great Quotes

This article is part of the CodeSmell Series.

How to Find the Stinky parts of your Code

Code Smell 142 — Queries in Constructors was originally published in Level Up Coding on Medium, where people are continuing the conversation by highlighting and responding to this story.


This content originally appeared on Level Up Coding - Medium and was authored by Maximiliano Contieri


Print Share Comment Cite Upload Translate Updates
APA

Maximiliano Contieri | Sciencx (2022-06-21T11:28:11+00:00) Code Smell 142 — Queries in Constructors. Retrieved from https://www.scien.cx/2022/06/21/code-smell-142-queries-in-constructors-2/

MLA
" » Code Smell 142 — Queries in Constructors." Maximiliano Contieri | Sciencx - Tuesday June 21, 2022, https://www.scien.cx/2022/06/21/code-smell-142-queries-in-constructors-2/
HARVARD
Maximiliano Contieri | Sciencx Tuesday June 21, 2022 » Code Smell 142 — Queries in Constructors., viewed ,<https://www.scien.cx/2022/06/21/code-smell-142-queries-in-constructors-2/>
VANCOUVER
Maximiliano Contieri | Sciencx - » Code Smell 142 — Queries in Constructors. [Internet]. [Accessed ]. Available from: https://www.scien.cx/2022/06/21/code-smell-142-queries-in-constructors-2/
CHICAGO
" » Code Smell 142 — Queries in Constructors." Maximiliano Contieri | Sciencx - Accessed . https://www.scien.cx/2022/06/21/code-smell-142-queries-in-constructors-2/
IEEE
" » Code Smell 142 — Queries in Constructors." Maximiliano Contieri | Sciencx [Online]. Available: https://www.scien.cx/2022/06/21/code-smell-142-queries-in-constructors-2/. [Accessed: ]
rf:citation
» Code Smell 142 — Queries in Constructors | Maximiliano Contieri | Sciencx | https://www.scien.cx/2022/06/21/code-smell-142-queries-in-constructors-2/ |

Please log in to upload a file.



There are no updates yet.
Click the Upload button above to add an update.

You must be logged in to translate posts. Please log in or register.

Related Posts