Tag: types

PostgreSQL NOTNULL vs IS NOT NULL vs NOT ISNULL

Today I’ve found out a flavor of PostgreSQL when checking if a composite type column is not null. There are different ways of checking for not null columns:

  • NOTNULL
  • IS NOT NULL
  • NOT ISNULL

For primitive values any of the above works, while for the composite types there is a particularity.

Given a table of users with a deleted column of a composite type action, and some users marked as deleted, I need all users that are deleted. Continue reading PostgreSQL NOTNULL vs IS NOT NULL vs NOT ISNULL

Types comparison and functions

PHP will let you change a variable’s type at any moment, and there’s nothing you can do about it. While you can use data structures, argument type declaration, and return type declaration to save a lot of damage, you can still change types.

<?php

declare(strict_types=1);

function showTypes(int $number) {
    echo gettype($number) . "\n"; //integer

    $number = "string";
    echo gettype($number) . "\n"; //string
}

showTypes(2);

In order to help this situation a little bit, I’m using the appropriate type comparison operators and functions:

<?php

$number = 1;

// OK
if ($number > 0) {}

// Not OK
if (!$number) {}
if ($number === '') {}
if (strlen($number) > 0) {}


$string = 'Lorem ipsum';

// OK
if ($string === '') {}
if (strlen($string) > 0) {}

// Not OK
if (!$string) {}


$list = [];

// OK
if (count($list) > 0) {}

// Not OK
if (!$list) {}


$bool = false;

// OK
if (true === $bool) {}
if (!$bool) {}

// Not OK
if ($bool == '') {}


$var = null; // if I know a var can be null

// OK
if (null === $var) {}
if (is_null($var)) {}

// Not OK
if (!$var) {}

As such, I’m being more specific about the type variables are holding. In clean code it’s faster to see what a variable holds, but in legacy systems you can see a variable hundreds of lines later after declaration, or you can get a value from a function with no return type or DocBlock.

Treat each variable as close as possible to its type.

Using data structures for types

Data types should be very specific. Anyone using a variable should know exactly what type it is, how it looks like (if it’s a structure). While for some languages it’s common sense and really enforced, others will let you mess with a variable’s type, no matter it’s a primitive, an object, an array.

I’m going to talk about data coming from JSON, databases or other sources, which can be represented into data structures.

In a language like Go, you map data into well defined structures.

package main

import (
    "encoding/json"
    "fmt"
)

type Person struct {
    ID int
    Age int
    Name string
}

func main() {
    string := `{
        "id":453,
        "age":26,
        "name":"John Doe"
    }`

    input := []byte(string)

    person := Person{}
    err := json.Unmarshal(input, &person)
    if err != nil {
        panic(err)
    }

    fmt.Println(person) // Person struct
    fmt.Println(person.ID) // integer
    fmt.Println(person.Age) // integer
    fmt.Println(person.Name) // string
}

You know exactly that you have an object of type Person, with integer ID, integer Age, and string Name. No need to check anything anywhere. If you mess up, you’ll know at compile time.

A dynamic typed language like PHP has a different approach. Continue reading Using data structures for types