How do I use a “not in list” type query for multiple columns in Kotlin Exposed?

Are you tired of writing complex queries to filter out unwanted data in your Kotlin Exposed database? Do you wish there was a simpler way to use a “not in list” type query for multiple columns? Well, wonder no more! In this article, we’ll take you on a journey to master the art of crafting efficient and elegant queries using Kotlin Exposed.

What is a “not in list” type query?

A “not in list” type query is a type of query that filters out rows from a table where a specific column’s value is not present in a given list of values. For example, let’s say you have a table called `users` with columns `id`, `name`, and `age`, and you want to retrieve all users whose `age` is not in the list `[18, 20, 25]`. A “not in list” type query would help you achieve this.

Why use Kotlin Exposed for database queries?

Kotlin Exposed is a lightweight, type-safe, and elegant ORM (Object-Relational Mapping) tool for Kotlin. It provides a simple and intuitive way to interact with your database, allowing you to write queries in a more functional programming style. With Kotlin Exposed, you can write concise and expressive queries that are easy to read and maintain.

The problem: Using “not in list” type queries for multiple columns

So, what happens when you want to use a “not in list” type query for multiple columns? For instance, suppose you want to retrieve all users whose `age` is not in `[18, 20, 25]` and whose `country` is not in `[“USA”, “Canada”]`. This is where things can get tricky.

The naive approach: Using multiple `notIn` clauses

One possible approach is to use multiple `notIn` clauses in your query. Here’s an example:
“`kotlin
val query = Users.select(Users.id, Users.name, Users.age, Users.country)
.where { (Users.age notIn listOf(18, 20, 25)) and (Users.country notIn listOf(“USA”, “Canada”)) }
“`

While this approach works, it can become cumbersome and error-prone when dealing with multiple columns and lists. Imagine having to write multiple `notIn` clauses for 5 or 10 columns!

The better approach: Using a single `notIn` clause with a combined list

Luckily, Kotlin Exposed provides a more elegant solution. You can combine the lists of values for each column into a single list of pairs, and then use a single `notIn` clause. Here’s how:
“`kotlin
val ages = listOf(18, 20, 25)
val countries = listOf(“USA”, “Canada”)
val combinedList = ages.map { it to “any” } + countries.map { “any” to it }

val query = Users.select(Users.id, Users.name, Users.age, Users.country)
.where { (Users.age to Users.country) notIn combinedList }
“`

By combining the lists of values for each column into a single list of pairs, you can use a single `notIn` clause to filter out unwanted data.

Advanced techniques: Using `notIn` with custom data types

But what if you’re working with custom data types, such as enums or custom classes? Kotlin Exposed provides an elegant way to use `notIn` with custom data types.

Using `notIn` with enums

Let’s say you have an enum class called `Color` with values `RED`, `GREEN`, and `BLUE`, and a table called `cars` with a column `color` of type `Color`. You can use `notIn` with enums like this:
“`kotlin
val colorsToExclude = listOf(Color.RED, Color.GREEN)
val query = Cars.select(Cars.id, Cars.model, Cars.color)
.where { Cars.color notIn colorsToExclude }
“`

Kotlin Exposed will automatically convert the enum values to their underlying database representation.

Using `notIn` with custom classes

Now, let’s say you have a custom class called `Address` with properties `street`, `city`, and `zip`, and a table called `users` with a column `address` of type `Address`. You can use `notIn` with custom classes like this:
“`kotlin
val addressesToExclude = listOf(
Address(“123 Main St”, “New York”, “10001”),
Address(“456 Broadway”, “Los Angeles”, “90001”)
)
val query = Users.select(Users.id, Users.name, Users.address)
.where { Users.address notIn addressesToExclude }
“`

Kotlin Exposed will automatically convert the custom class instances to their underlying database representation.

Best practices for using “not in list” type queries

Here are some best practices to keep in mind when using “not in list” type queries in Kotlin Exposed:

• Use meaningful variable names: Choose variable names that clearly indicate what the list contains, such as `agesToExclude` or `countriesToSkip`.
• Avoid using `notIn` with large lists: Using `notIn` with very large lists can lead to performance issues. Instead, consider using alternative query methods or optimizing your database schema.
• Use `notIn` with caution in subqueries: When using `notIn` in subqueries, be careful not to create correlated subqueries that can slow down your query.

Conclusion

In this article, we’ve explored the world of “not in list” type queries in Kotlin Exposed, covering the basics, advanced techniques, and best practices. By mastering these techniques, you’ll be able to write more efficient, elegant, and maintainable queries that make your database interactions a breeze.

Remember, Kotlin Exposed is a powerful tool that can help you simplify your database interactions. With its intuitive API and strong type safety, you can focus on writing business logic rather than worrying about the underlying database complexity.

So, go ahead and give Kotlin Exposed a try! Your database – and your code – will thank you.

Query Type	Example Query
Simple “not in list” query	Users.select(Users.id, Users.name, Users.age).where { Users.age notIn listOf(18, 20, 25) }
“not in list” query for multiple columns	Users.select(Users.id, Users.name, Users.age, Users.country).where { (Users.age to Users.country) notIn combinedList }
“not in list” query with enums	Cars.select(Cars.id, Cars.model, Cars.color).where { Cars.color notIn colorsToExclude }
“not in list” query with custom classes	Users.select(Users.id, Users.name, Users.address).where { Users.address notIn addressesToExclude }

Note: The code examples in this article are simplified for illustration purposes. In a real-world scenario, you may need to handle errors, edge cases, and other complexities.

Frequently Asked Question

Get ready to master the art of querying in Kotlin Exposed! Here are five questions and answers to help you navigate the world of “not in list” type queries for multiple columns.