My earlier article launched Ktor and a few of its fundamental options for constructing internet purposes. Now, we’ll increase the instance software developed in that article by including persistent knowledge and HTMX, which is able to present extra interactive views. This provides us a setup with a number of energy in a comparatively easy stack.
Please see the earlier article for the instance software code and setup. We’ll construct on that instance right here.
Add persistence to the Ktor-HTMX software
Step one towards making our software extra highly effective is so as to add persistent knowledge. The most well-liked method to work together with an SQL database in Kotlin is with the Uncovered ORM framework. It provides us a few methods to work together with the database, utilizing both a DAO mapping or a DSL. Kotlin’s native syntax means the general really feel of utilizing the ORM mapping layer has much less overhead than others you may need encountered.
We’ll want so as to add a couple of dependencies to our construct.gradle.kt, along with these we have already got:
dependencies {
// present deps...
implementation("org.jetbrains.uncovered:exposed-core:0.41.1")
implementation("org.jetbrains.uncovered:exposed-jdbc:0.41.1")
implementation("com.h2database:h2:2.2.224")
}
You’ll discover we’ve included the uncovered core and JDBC libraries, in addition to a driver for the in-memory H2 database. We’ll use H2 as a easy persistence mechanism that may simply be converted to an exterior SQL database like Postgres afterward.
Add companies
To begin with, we’ll create a few easy companies that work together with a principal service, which talks to the database. Right here’s our QuoteSchema.kt file thus far, which units up the database schema and supplies service features for interacting with it:
// src/principal/kotlin/com/instance/plugins/QuoteSchema.kt
bundle com.instance.plugins
import kotlinx.coroutines.*
import org.jetbrains.uncovered.sql.*
import org.jetbrains.uncovered.sql.transactions.transaction
object Quotes : Desk() {
val id: Column = integer("id").autoIncrement()
val quote = textual content("quote")
val writer = textual content("writer")
override val primaryKey = PrimaryKey(id, identify = "PK_Quotes_ID")
}
knowledge class Quote(val id: Int? = null, val quote: String, val writer: String)
class QuoteService {
droop enjoyable create(quote: Quote): Int = withContext(Dispatchers.IO) {
transaction {
Quotes.insert {
it[this.quote] = quote.quote
it[this.author] = quote.writer
} get Quotes.id
} ?: throw Exception("Unable to create quote")
}
droop enjoyable record(): Record = withContext(Dispatchers.IO) {
transaction {
Quotes.selectAll().map {
Quote(
id = it[Quotes.id],
quote = it[Quotes.quote],
writer = it[Quotes.author]
)
}
}
}
}
There’s quite a bit occurring on this file, so let’s take it step-by-step. The very first thing we do is declare a Quotes object that extends Desk. Desk is part of the Uncovered framework and lets us outline a desk within the database. It does a number of work for us based mostly on the 4 variables we outline: id, quote, writer, and major key. The id aspect shall be auto-generated for an auto-increment major key, whereas the opposite two may have their applicable column varieties (textual content turns into string, for instance, relying on the database’s dialect and driver).
Uncovered can be good sufficient to solely generate the desk if it doesn’t exist already.
Subsequent, we declare an information class known as Quote, utilizing the constructor fashion. Discover id is marked as non-obligatory (since it will likely be auto-generated).
Then, we create a QuoteService class with two suspendable features: create and record. These are each interacting with the concurrent assist in Kotlin, utilizing the IO dispatcher. These strategies are optimized for IO-bound concurrency, which is suitable for database entry.
Inside every service methodology, we have now a database transaction, which does the work of both inserting a brand new Quote or returning a Record of Quotes.
Routes
Now let’s make a Database.kt file that pulls within the QuoteService and exposes endpoints for interacting with it. We’ll want a POST for creating quotes and a GET for itemizing them.
//src/principal/kotlin/com/instance/plugins/Database.kt
bundle com.instance.plugins
import io.ktor.http.*
import io.ktor.server.software.*
import io.ktor.server.request.*
import io.ktor.server.response.*
import io.ktor.server.routing.*
import java.sql.*
import kotlinx.coroutines.*
import org.jetbrains.uncovered.sql.*
import org.jetbrains.uncovered.sql.transactions.transaction
enjoyable Utility.configureDatabases() {
val database = Database.join(
url = "jdbc:h2:mem:take a look at;DB_CLOSE_DELAY=-1",
person = "root",
driver = "org.h2.Driver",
password = "",
)
transaction {
SchemaUtils.create(Quotes)
}
val quoteService = QuoteService()
routing {
submit("/quotes") {
val parameters = name.receiveParameters()
val quote = parameters["quote"] ?: ""
val writer = parameters["author"] ?: ""
val newQuote = Quote(quote = quote, writer = writer)
val id = quoteService.create(newQuote)
name.reply(HttpStatusCode.Created, id)
}
get("/quotes") {
val quotes = quoteService.record()
name.reply(HttpStatusCode.OK, quotes)
}
}
}
We start through the use of Database.join from the Uncovered framework to create a database connection utilizing normal H2 parameters. Then, inside a transaction we create the Quotes schema, utilizing our Quotes class we outlined in QuoteSchema.kt.
Subsequent, we create two routes utilizing the syntax we developed in the primary stage of this instance and counting on the create and record features and Quote class from QuoteSchema.
Don’t neglect to incorporate the brand new operate in Utility.kt:
// src/principal/kotlin/com/instance/Utility.kt
bundle com.instance
import com.instance.plugins.*
import io.ktor.server.software.*
import io.ktor.server.response.*
import io.ktor.server.routing.*
enjoyable principal(args: Array) {
io.ktor.server.netty.EngineMain.principal(args)
}
enjoyable Utility.module() {
configureTemplating()
//configureRouting()
set up(RequestLoggingPlugin)
configureDatabases()
}
Discover I’ve commented out the previous configureRouting() name, so it gained’t battle with our new routes.
To do a fast take a look at of those routes, we are able to use the curl command-line instrument. This line inserts a row:
$ curl -X POST -H "Content material-Sort: software/x-www-form-urlencoded" -H "Host: localhost:8080" -d "quote=FooBar.&writer=William+Shakespeare" http://localhost:8080/quotes
And this one outputs the prevailing rows:
$ curl http://localhost:8080/quotes
Utilizing HTMX for interactive views
Now let’s leap proper into making a UI to work together with the companies utilizing HTMX. We wish a web page that lists the prevailing quotes and a type that we are able to use to submit a brand new quote. The quote shall be dynamically inserted into the record on the web page, and not using a web page reload.
To attain these objectives, we’ll want a route that pulls every thing on the outset after which one other route that accepts the shape POST and returns the markup for the newly inserted quote. We’ll add these to the Database.kt routes for simplicity.
Right here is the /quotes-htmx web page that offers us the preliminary record and type:
get("/quotes-htmx") {
val quotes = quoteService.record()
name.respondHtml {
head {
script(src = "https://unpkg.com/htmx.org@1.9.6") {}
}
physique {
h1 { +"Quotes (HTMX)" }
div {
id = "quotes-list"
quotes.forEach { quote ->
div {
p { +quote.quote }
p { +"― ${quote.writer}" }
}
}
}
type(methodology = FormMethod.submit, motion = "/quotes", encType = FormEncType.applicationXWwwFormUrlEncoded) {
attributes["hx-post"] = "/quotes"
attributes["hx-target"] = "#quotes-list"
attributes["hx-swap"] = "beforeend"
div {
label { +"Quote:" }
textInput(identify = "quote")
}
div {
label { +"Writer:" }
textInput(identify = "writer")
}
button(kind = ButtonType.submit) { +"Add Quote" }
}
}
}
}
First, we seize the record of quotes from the service. Then we begin outputting the HTML, starting with a head aspect that features the HTMX library from a CDN. Subsequent, we open a physique tag and render a title (H1) aspect adopted by a div with the id of quotes-list. Discover that id is dealt with as a name from contained in the div block, as a substitute of as an attribute on div.
Inside quotes-list, we iterate over the quotes assortment and output a div with every quote and writer. (Within the Specific model of this software, we used a UL and record objects. We might have finished the identical right here.)
After the record comes the shape, which units a number of non-standard attributes (hx-post, hx-target, and hx-swap) on the attributes assortment. These shall be set on the output HTML type aspect.
Now all we want is a /quotes route to simply accept the incoming quotes from POST and reply with an HTML fragment that represents the brand new quote to be inserted into the record:
submit("/quotes") {
val parameters = name.receiveParameters()
val quote = parameters["quote"] ?: ""
val writer = parameters["author"] ?: ""
val newQuote = Quote(quote = quote, writer = writer)
val id = quoteService.create(newQuote)
val createdQuote = quoteService.learn(id)
name.respondHtml(HttpStatusCode.Created) {
physique{
div {
p { +createdQuote.quote }
p { +"― ${createdQuote.writer}" }
}
}
}
That is fairly simple. One wrinkle is that Kotlin’s HTML DSL doesn’t prefer to ship an HTML fragment, so we have now to wrap our quote markup in a physique tag, which shouldn’t be there. (There’s a easy workaround we’re skipping for simplicity, present in this venture known as respondHtmlFragment). It appears possible that producing HTML fragments will finally develop into an ordinary a part of the HTML DSL.
Apart from that, we simply parse the shape and use the service to create a Quote after which use the brand new Quote to generate the response, which HTMX will use to replace the UI dynamically.
Conclusion
We went quick and lean with this instance, to discover the essence of Ktor. Nonetheless, we have now all the weather of a extremely performant and dynamic stack with out a lot overhead. As a result of Kotlin is constructed on high of the JVM it provides you entry to every thing Java does. That, coupled with its highly effective union of object-oriented and useful programming, and DSL capabilities, makes Kotlin a compelling server-side language. You should use it for constructing purposes with conventional RESTful JSON endpoints, or with dynamic HTMX-powered UIs, as we’ve seen right here.
See my GitHub repository for the whole supply code for the Ktor-HTMX software instance.