readme.md

Code Smell 50 - Object Keys

Primary keys, IDs, references. The first attribute we add to our objects. They don't exist in the real-world.

TL;DR: Reference objects with objects, not ids.

Problems

• Coupling

• Accidental Implementation

• Bijection Principle Violation.

Solutions

1. Reference object to objects.

2. Build a MAPPER.

3. Only use keys if you need to provide an external (accidental) reference. Databases, APIs, Serializations.

4. Use dark keys or GUIDs when possible.

5. If you are afraid of getting a big relation graph use proxies or lazy loading.

6. Don't use DTOs.

Code Smell 40 - DTOs

Sample Code

Wrong

class Teacher {
    static getByID(id) {
        // This is coupled to the database
        // Thus violating separation of concerns
    }

    constructor(id, fullName) {
        this.id = id;
        this.fullName = fullName;
    }
}

class School {
    static getByID(id) {
        // go to the coupled database
    }

    constructor(id, address) {
        this.id = id;
        this.address = address;
    }
}

class Student {
    constructor(firstName, lastName, id, teacherId, schoolId) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.id = id;
        this.teacherId = teacherId;
        this.schoolId = schoolId;
    }

    school() {
        return School.getById(this.schoolId);
    }

    teacher() {
        return Teacher.getById(this.teacherId);
    }
}

Right

class Teacher {
    constructor(fullName) {
        this.fullName = fullName;
    }
}

class School {
    constructor(address) {
        this.address = address;
    }
}

class Student {
    constructor(firstName, lastName, teacher, school) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.teacher = teacher;
        this.school = school;
    }
}

// The ids are no longer needed since they don’t exist in the real world.
// If you need to expose a School to an external API or a database,
// another object (not school)
// will keep the mapping externalId<->school and so on

Detection

This is a design policy.

We can enforce business objects to warn us if we define an attribute or function including the sequence id.

Tags

• Accidental

Conclusion

Ids are not necessary for OOP. You reference objects (essential) and never ids (accidental).

In case you need to provide a reference out of your system's scope (APIs, interfaces, Serializations) use dark and meaningless IDs (GUIDs).

Relations

Code Smell 20 - Premature Optimization

More Info

What is (wrong with) software?

The One and Only Software Design Principle

Coupling - The one and only software design problem

Credits

Photo by Maurice Williams on Unsplash

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All problems in computer science can be solved by another level of indirection.

David Wheeler

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Software Engineering Great Quotes

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This article is part of the CodeSmell Series.

How to Find the Stinky Parts of your Code