LHSK (LHS brackets parser and utilities for Kotlin and Exposed)

Table of Contents

• Introduction
• Features
• Installation
• Usage
• Supported operators
• Valid SQL types
• Contributing
• License
• Acknowledgments

Introduction

LHS brackets is a flexible and powerful tool to add filters and sorts on REST requests as query params. Example:

/api/search/data?property_type[eq]=PARKING&deposit_amount[lte]=604.75&sort[0]=auction_value:asc    

This library provides utilities to parse LHS brackets syntax, generate it and also to easily apply them to database queries via Exposed library.

Features

• Easy integration with Kotlin projects.
• Comprehensive API for database interactions using Exposed.
• Support for join queries in Exposed.
• Supports Java SDK version 11 and Kotlin API version 1.9.

Installation

Gradle

Add the following dependencies to your build.gradle.kts file:

dependencies {
    implementation("io.github.elfogre:lhs-parser:1.0.3")
    implementation("io.github.elfogre:lhs-exposed:1.0.3")
}

Usage

Example 1: Basic Parser Usage (usin Ktor request params)

import io.github.elfogre.LHSBracketsParser

fun main() {
    val searchParams = LHSBracketsParser.parseSearchQueryParams(call.request.queryParameters.flattenEntries())
        ...
}

Example 2: Database Interaction with Exposed

Use exact table column names as property types on LHS.

import io.github.elfogre.LHSBracketsExposedExtension
import org.jetbrains.exposed.sql.transactions.transaction

fun main() {
    ...
    transaction {
        CarTable.
        selectAll().
        addWhereExpressionFromLHSFilter(parsedParams.filters).
        addOrderByFromLHSSort(parsedParams.sorts).
        map { Car.fromResultRow(it) }
    }
}

Filter and sort operations accepts a list of fields to exclude them from sorting and filtering.

Why Use Excluded Fields?

• Prevent Performance Issues: Filtering by non-indexed fields can severely impact database performance.
• Protect Internal Logic Fields: Avoid exposing and filtering by fields that are used for internal logic and should not be accessible externally.

Check for more examples in integration tests.

Example 3: LHS brackets syntax generation

import io.github.elfogre.LHSBracketsParser

fun main() {
    val queryParams = LHSBracketsParser.searchParamsToLHSBracketsQueryParams(searchParams)
        ...
}

Supported operators

• eq: Equal to
• neq: Not equal to
• gt: Greater than
• gte: Greater than or equal to
• lt: Less than
• lte: Less than or equal to
• in: In a specified list of values (Use a comma separated list as value)
• notin: Not in a specified list of values (Use a comma separated list as value)

Valid SQL types

Supported exposed column types for automatic casting in lhs-exposed are:

• StringColumnType
• LongColumnType
• CustomEnumerationColumnType
• IntegerColumnType
• DecimalColumnType

Contributing

We welcome contributions! Please add issues or submit a pull request.

License

This project is licensed under the GNU GPL License - see the LICENSE file for details.

Acknowledgments

• Thanks to the Exposed and Kotlin teams for their invaluable libraries.