How to Fix Query Error in Kotlin

If you've run into a query error in your Kotlin project, you're not alone. This is one of the most common issues developers face, and fortunately the fix is usually straightforward once you understand the root cause.

Common Causes

Query errors in Kotlin usually stem from one of these issues:

• Malformed SQL syntax or incorrect query builder usage
• Missing, null, or incorrectly typed parameters
• Type mismatches between query parameters and database column types
• Attempting to access results from an empty result set
• Connection pool exhaustion under high load

The Fix

// Using Exposed framework with transaction
val user = transaction {
    Users
        .select { Users.id eq userId }
        .map { row ->
            User(
                id = row[Users.id],
                name = row[Users.name],
                email = row[Users.email]
            )
        }
        .singleOrNull()
} ?: throw NotFoundException("User $userId not found")

Use singleOrNull() and handle the null case with Kotlin's elvis operator for concise error handling.

Preventing Query Errors

• Use an ORM or query builder to reduce raw SQL mistakes and prevent injection
• Validate input types before passing them to queries
• Handle empty results explicitly rather than assuming data always exists
• Log the full query text (without sensitive data) when errors occur for debugging
• Monitor slow queries to catch performance issues before they become errors

Let [Bugsly](https://bugsly.dev) capture and group query errors in your Kotlin app so you can see exactly which queries are failing, how often, and with what parameters.