kotliquery: A Kotlin repository from joaomneto

KotliQuery

A handy RDB client library in Kotlin. Highly inspired from ScalikeJDBC. This library focuses on providing handy and Kotlin-ish API to issue a query and extract values from its JDBC ResultSet iterator.

Getting Started

You can try this library with Gradle right now. See the sample project:

https://github.com/seratch/kotliquery/tree/master/sample

build.gradle

apply plugin: 'kotlin'

buildscript {
    ext.kotlin_version = '1.3.11'
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}
repositories {
    mavenCentral()
}
dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    compile 'com.github.seratch:kotliquery:1.3.0'
    compile 'com.h2database:h2:1.4.197'
    compile 'com.zaxxer:HikariCP:3.2.0'
}

Example

KotliQuery is very easy-to-use. After reading this short documentation, you will have learnt enough.

Creating DB Session

Session object, thin wrapper of java.sql.Connection instance, runs queries.

import kotliquery.*

val session = sessionOf("jdbc:h2:mem:hello", "user", "pass")

HikariCP

Using connection pool would be better for serious programming.

HikariCP is blazingly fast and so handy.

HikariCP.default("jdbc:h2:mem:hello", "user", "pass")

using(sessionOf(HikariCP.dataSource())) { session ->
   // working with the session
}

DDL Execution

session.run(queryOf("""
  create table members (
    id serial not null primary key,
    name varchar(64),
    created_at timestamp not null
  )
""").asExecute) // returns Boolean

Update Operations

val insertQuery: String = "insert into members (name,  created_at) values (?, ?)"

session.run(queryOf(insertQuery, "Alice", Date()).asUpdate) // returns effected row count
session.run(queryOf(insertQuery, "Bob", Date()).asUpdate)

Select Queries

Prepare select query execution in the following steps:

Create Query object by using queryOf factory
Bind extractor function ((Row) -> A) to the Query object via #map method
Specify response type (asList/asSingle) at the end

val allIdsQuery = queryOf("select id from members").map { row -> row.int("id") }.asList
val ids: List<Int> = session.run(allIdsQuery)

Extractor function can return any type of result from ResultSet.

data class Member(
  val id: Int,
  val name: String?,
  val createdAt: java.time.ZonedDateTime)

val toMember: (Row) -> Member = { row -> 
  Member(
    row.int("id"), 
    row.stringOrNull("name"), 
    row.zonedDateTime("created_at")
  )
}

val allMembersQuery = queryOf("select id, name, created_at from members").map(toMember).asList
val members: List<Member> = session.run(allMembersQuery)

val aliceQuery = queryOf("select id, name, created_at from members where name = ?", "Alice").map(toMember).asSingle
val alice: Member? = session.run(aliceQuery)

Named query parameters

Alternative syntax is supported to allow named parameters in all queries.

queryOf("""select id, name, created_at 
	from members 
	where (:name is not null or name = :name)
	  and (:age is not null or age = :age)""", 
	mapOf("name" to "Alice"))

In the query above, the param age is not supplied on purpose.

Performance-wise this syntax is slightly slower to prepare the statement and a tiny bit more memory-consuming, due to param mapping. Use it if readability is a priority.

Importantly, this method is not based on "artificial" string replacement. In fact, the statement is prepared just as if it was the default syntax.

Typed params

In the case, the parameter type has to be explicitly stated, there's a wrapper class - Parameter that will help provide explicit type information.

val param = Parameter(param, String::class.java)
queryOf("""select id, name 
    from members 
    where ? is null or ? = name""", 
    param, param)

or also with the helper function param

queryOf("""select id, name 
    from members 
    where ? is null or ? = name""", 
    null.param<String>(), null.param<String>())

This can be useful in situations similar to one described here.

Working with Large Dataset

#forEach allows you to make some side-effect in iterations. This API is useful for handling large ResultSet.

session.forEach(queryOf("select id from members")) { row ->
  // working with large data set
})

Transaction

Session object provides transaction block.

session.transaction { tx ->
  // begin
  tx.run(queryOf("insert into members (name,  created_at) values (?, ?)", "Alice", Date()).asUpdate)
}
// commit

session.transaction { tx ->
  // begin
  tx.run(queryOf("update members set name = ? where id = ?", "Chris", 1).asUpdate)
  throw RuntimeException() // rollback
}

License

(The MIT License)

joaomneto/kotliquery