elastic4s - Elasticsearch Scala Client

Elastic4s is mostly a wrapper around the standard Elasticsearch Java client with the intention of creating a concise, idiomatic, reactive, type safe DSL for applications in Scala that use Elasticsearch. The Java client, which can of course be used directly in Scala, is more verbose due to Java's nature. Scala lets us do better.

Elastic4s's DSL allows you to to construct your requests programatically, with syntatic and semantic errors manifested at compile time, and uses standard Scala futures to enable you to easily integrate into your existing asynchronous workflow. The aim of the DSL is that requests are written in an SQL-like way, while staying true to the Java API or Rest API.

Elastic4s supports Scala collections so you don't have to do tedious conversions from your Scala domain classes into Java collections. It also allows you to index documents directly without having to extract and set fields manually - eg from a case class, a JSON document, or a Map (or a custom source). Due to its type safe nature, it is easy to see what operations are available for any request type, because your IDE can use type information to show what methods are available.

Key points

Type safe concise DSL
Reactive / Scala futures
Scala collections
Leverages Java library
SQL-style requests

Release

The latest release is 1.5.10 which is compatible with Elasticsearch 1.5.x. There are releases for both Scala 2.10 and Scala 2.11. For releases that are compatible with earlier versions of Elasticsearch, search maven central. For more information read Using Elastic4s in your project.

Elastic4s Release	Target Elasticsearch version
1.5.10	1.5.X
1.4.13	1.4.x
1.3.3	1.3.x
1.2.3.0	1.2.x
1.1.2.0	1.1.x
1.0.3.0	1.0.x
0.90.13.2	0.90.x

Dependencies

Starting from version 1.2.1.3, if you want to use Jackson for JSON in ObjectSource, the following dependencies are required in your project:

"com.fasterxml.jackson.core" % "jackson-core" % "2.4.2"
"com.fasterxml.jackson.core" % "jackson-databind" % "2.4.2"
"com.fasterxml.jackson.module" %% "jackson-module-scala" % "2.4.2"

Introduction

The basic usage of the Scala driver is that you create an instance of ElasticClient and then invoke the various execute methods with the requests you want to perform. The execute methods are asynchronous and will return a standard Scala Future[T] where T is the response type appropriate for your request type. For example a search request will return a response of type SearchResponse which contains the results of the search.

Requests, such as inserting a document, searching, creating an index, etc, are created using the DSL syntax that is similar in style to SQL queries. For example to create a search request, you would do: search in "index/type" query "findthistext"

The response objects are, for the most part, the exact same type the Java API returns. This is because there is mostly no reason to wrap these as they are fairly easy to use in Scala.

All the DSL keywords are located in the ElasticDsl trait which needs to be imported or extended.

An example is worth 1000 characters so here is a quick example of how to create a local node with a client and index a one field document. Then we will search for that document using a simple text query.

import com.sksamuel.elastic4s.ElasticClient
import com.sksamuel.elastic4s.ElasticDsl._

object Test extends App {

  val client = ElasticClient.local

  // await is a helper method to make this operation synchronous instead of async
  // You would normally avoid doing this in a real program as it will block your thread
  client.execute { index into "bands" / "artists" fields "name"->"coldplay" }.await

  val resp = client.execute { search in "bands" / "artists" query "coldplay" }.await
  println(resp)

}

For more in depth examples keep reading.

Syntax

Here is a list of the common requests and the syntax used to create them. For more details on each request click through to the readme page. For options that are not yet documented, refer to the Elasticsearch documentation as the DSL closely mirrors the standard Java API / REST API.

Operation	Syntax
Add Alias	`add alias "<alias>" on "<index>"`
Clear index cache	`clear cache <name>`
Close index	`close index <name>`
Count	`count from <indexes> types <types> <queryblock>`
Create Index	`create index <name> mappings { mappings block> } [settings]`
Create Repository	`create repository <repo> type <type> settings <settings>`
Create Snapshot	`create snapshot <name> in <repo> ...`
Create Template	`create template <name> pattern <pattern> mappings {...}`
Delete by id	`delete id <id> from <index/type> [settings]`
Delete by query	`delete from <index/type> query { <queryblock> } [settings]`
Delete index	`delete index <index> [settings]`
Delete Mapping	`delete mapping <index/type>`
Delete Snapshot	`delete snapshot <name> in <repo> ...`
Delete Template	`delete template <name>`
Explain	`explain id <id> in <index/type> query { <queryblock> }`
Flush Index	`flush index <name>`
Get	`get id <id> from <index/type> [settings]`
Get Alias	`get alias <name> on <index>`
Get Mapping	`get mapping <index> / <type>`
Get Snapshot	`get snapshot <name> from <repo>`
Index	`index into <index/type> fields { <fieldblock> } [settings]`
Index exists	`index exists <name>`
Index Status	`status <index>`
More like this	`morelike id <id> in <index/type> { fields <fieldsblock> } [settings]`
Multiget	`multiget ( get id 1 from index, get id 2 from index, ... )`
Multisearch	`multi ( search in <index/type> query, search in <index/type> query, ...)`
Open index	`open index <name>`
Optimize	`optimize index "indexname" [settings]`
Percolate Doc	`percolate in <index> { fields <fieldsblock> }`
Put mapping	`put mapping <index> / <type> add { mappings block }`
Register Query	`register id <id> into <index> query { <queryblock> }`
Recover Index	`recover index <name>`
Refresh index	`refresh index <name>`
Restore Snapshot	`restore snapshot <name> from <repo> ...`
Remove Alias	`remove alias "<alias>" on "<index>"`
Search	`search in <index/type> query ... postFilter ... sort ...`
Search scroll	`search scroll <scrollId>`
Validate	`validate in <index/type> query <queryblock>`
Update	`update id <id> in <index/type> script <script> [settings]`

Please also note some java interoperability notes.

Client

A locally configured node and client can be created simply by invoking local on the ElasticClient object:

import com.sksamuel.elastic4s.ElasticClient
val client = ElasticClient.local

To specify settings for the local node you can pass in a settings object like this:

val settings = ImmutableSettings.settingsBuilder()
      .put("http.enabled", false)
      .put("path.home", "/var/elastic/")
val client = ElasticClient.local(settings.build)

To connect to a remote elastic cluster then you need to use the remote() call specifying the hostnames and ports. Please note that this is the port for the TCP interface (normally 9300) and NOT the port you connect with when using HTTP (normally 9200).

// single node
val client = ElasticClient.remote("host1", 9300)

For multiple nodes it's better to use the elasticsearch client uri connection string. This is in the format "elasticsearch://host:port,host:port,..." (Note, no parameters can be added). For example:

val uri = ElasticsearchClientUri("elasticsearch://foo:1234,boo:9876")
val client = ElasticClient.remote(uri)

If you need to pass settings to the client, then you need to invoke remote() with a settings object. For example to specify the cluster name (if you changed the default then you must specify the cluster name).

import org.elasticsearch.common.settings.ImmutableSettings
val settings = ImmutableSettings.settingsBuilder().put("cluster.name", "myClusterName").build()
val client = ElasticClient.remote(settings, ElasticsearchClientUri("elasticsearch://somehost:9300"))

If you already have a handle to a Node in the Java API then you can create a client from it easily:

val node = ... // node from the java API somewhere
val client = ElasticClient.fromNode(node)

Create Index

All documents in Elasticsearch are stored in an index. We do not need to tell Elasticsearch in advance what an index will look like (eg what fields it will contain) as Elasticsearch will adapt the index dynamically as more documents are added, but we must at least create the index first.

To create an index called "places" that is fully dynamic we can simply use:

client.execute { create index "places" }

We can optionally set the number of shards and / or replicas

client.execute { create index "places" shards 3 replicas 2 }

Sometimes we want to specify the properties of the fields in the index in advance. This allows us to manually set the type of the field (where Elasticsearch might infer something else) or set the analyzer used, or multiple other options

To do this we add mappings:

import com.sksamuel.elastic4s.mappings.FieldType._
import com.sksamuel.elastic4s.StopAnalyzer

client.execute {
    create index "places" mappings (
        "cities" as (
            "id" typed IntegerType,
            "name" typed StringType boost 4,
            "content" typed StringType analyzer StopAnalyzer
        )
    )
}

Then Elasticsearch is configured with those mappings for those fields only. It is still fully dynamic and other fields will be created as needed with default options. Only the fields specified will be "fixed".

More examples on the create index syntax can be found here.

Analyzers

Analyzers control how Elasticsearch parses the fields for indexing. For example, you might decide that you want whitespace to be important, so that "band of brothers" is indexed as a single "word" rather than the default which is to split on whitespace. There are many advanced options available in analayzers. Elasticsearch also allows us to create custom analyzers. For more details read about the DSL support for analyzers.

Indexing

To index a document we need to specify the index and type and optionally we can set an id. If we don't include an id then elasticsearch will generate one for us. We must also include at least one field. Fields are specified as standard tuples.

client.execute {
  index into "places" / "cities" id "uk" fields (
    "name" -> "London",
    "country" -> "United Kingdom",
    "continent" -> "Europe",
    "status" -> "Awesome"
  )
}

There are many additional options we can set such as routing, version, parent, timestamp and op type. See official documentation for additional options, all of which exist in the DSL as keywords that reflect their name in the official API.

Sometimes it is useful to seperate the knowledge of the type from the indexing logic. For this we can use the DocumentSource or DocumentMap abstractions. A quick example.

case class Band(name: String, albums: Seq[String], label: String)
val band = Band("coldplay", Seq("X&Y", "Parachutes"), "Parlophone")

client.execute {
  // the band object will be implicitly converted into a DocumentSource
  index into "music" / "bands" doc band
}

Here Elastic4s has implicitly converted your case class into a DocumentSource and all fields would be indexed against the field name. You can control this at a more fine grained level if required. More details on the document traits page.

Beautiful!

Searching

Searching is naturally the most involved operation. There are many ways to do searching in elastic search and that is reflected in the higher complexity of the query DSL.

To do a simple text search, where the query is parsed from a single string

search in "places" / "cities" query "London"

That is actually an example of a SimpleStringQueryDefinition. The string is implicitly converted to that type of query. It is the same as specifying the query type directly:

search in "places"- / "cities" query simpleStringQuery("London")

The simple string example is the only time we don't need to specify the query type. We can search for everything by not specifying a query at all.

search in "places" / "cities"

We might want to limit the number of results and / or set the offset.

search in "places" / "cities" query "paris" start 5 limit 10

We can search against certain fields only:

search in "places" / "cities" query termQuery("country", "France")

Or by a prefix:

search in "places" / "cities" query prefixQuery("country", "France")

Or by a regular expression (slow, but handy sometimes!):

search in "places" / "cities" query regexQuery("country", "France")

There are many other types, such as range for numeric fields, wildcards, distance, geo shapes, matching.

Read more about search syntax here. Read about multisearch here.

Highlighting

Elasticsearch can annotate results to show which part of the results matched the queries by using highlighting. Just think when you're in google and you see the snippets underneath your results - that's what highlighting does.

We can use this very easily, just add a highlighting definition to your search request, where you set the field or fields to be highlighted. Viz:

search in "music" / "bios" query "kate bush" highlighting (
  highlight field "body" fragmentSize 20
)

All very straightforward. There are many options you can use to tweak the results. In the example above I have simply set the snippets to be taken from the field called "body" and to have max length 20. You can set the number of fragments to return, seperate queries to generate them and other things. See the elasticsearch page on highlighting for more info.

Get

Sometimes we don't want to search and want to retrieve a document directly from the index by id. In this example we are retrieving the document with id 'coldplay' from the bands/rock index and type.

client.execute {
 get id "coldplay" from "bands" / "rock"
}

We can get multiple documents at once too. Notice the following multiget wrapping block.

client.execute {
  multiget(
    get id "coldplay" from "bands/rock",
    get id "keane" from "bands/rock"
  )
}

See more get examples and usage of multiget here

Deleting

In the rare case that we become tired of a band we might want to remove them. Naturally we wouldn't want to remove Chris Martin and boys so we're going to remove U2 instead. We think they're a little past their best (controversial). This operation assumes the id of the document is "u2".

client.execute {
  delete id "u2" from "bands/rock"
}

We can take this a step further by deleting by a query rather than id. In this sense the delete is very similar to an SQL delete statement. In this example we're deleting all bands where their type is rap.

client.execute {
    delete from index "bands" types "rock" where termQuery("type", "rap")
}

See more about delete on the delete page

Updates

We can update existing documents without having to do a full index, by updating a partial set of fields.

client.execute {
  update 25 in "scifi/starwars" docAsUpsert (
    "character" -> "chewie",
    "race" -> "wookie"
  )
}

Read more about updates and see more examples.

More like this

If you want to return documents that are "similar" to a current document we can do that very easily with the more like this query.

client.execute {
  morelike id 4 from "beers/lager" percentTermsToMatch 0.5
}

For all the options see here.

Bulk Operations

Elasticsearch is fast. Roundtrips are not. Sometimes we want to wrestle every last inch of performance and a useful way to do this is to batch up requests. Elastic has guessed our wishes and created the bulk API. To do this we simply wrap index, delete and update requests using the bulk keyword and pass to the execute method in the client.

client.execute {
  bulk (
    index into "bands/rock" fields "name"->"coldplay",
    index into "bands/rock" fields "name"->"kings of leon",
    index into "bands/pop" fields (
      "name"->"elton john",
      "best_album"->"tumbleweed connection"
    )
  )
}

A single HTTP or TCP request is now needed for 4 operations. In addition Elasticsearch can now optimize the requests, by combinging inserts or using aggressive caching.

The example above uses simple documents just for clarity of reading; the usual optional settings can still be used. See more information on the bulk page.

Synchronous Operations

All operations are normally asynchronous. Sometimes though you might want to block - for example when doing snapshots or when creating the initial index. You can call .await on any operation to block until the result is ready. This is especially useful when testing.

val resp = client.execute { index into "bands/rock" fields ("name"->"coldplay", "debut"->"parachutes") }.await
resp.isInstanceOf[IndexResponse] // true

Helpers

Helpers provide higher level APIs to work with Elasticsearch.

Reindexing data

Use the reindex helper to reindex data from source index to target index.

client.reindex(
  sourceIndex = "sourceIndex",
  targetIndex = "targetIndex",
  chunkSize = 500,
  scroll = "5m")

DSL Completeness

As it stands the Scala DSL covers all of the common operations - index, create, delete, delete by query, search, validate, percolate, update, explain, get, and bulk operations. There is good support for the various settings for each of these - more so than the Java client provides in the sense that more settings are provided in a type safe manner.

However there are settings and operations (mostly admin / cluster related) that the DSL does not yet cover (pull requests welcome!). In these cases it is necessary to drop back to the Java API. This can be done by calling .java on the client object to get the underlying java elastic client, or .admin to get the admin based client, eg, the following request is a Java API request.

client.admin.cluster.prepareHealth.setWaitForEvents(Priority.LANGUID).setWaitForGreenStatus().execute().actionGet

This way you can still access everything the normal Java client covers in the cases where the Scala DSL is missing a construct, or where there is no need to provide a DSL.

Using Elastic4s in your project

For gradle users, add:

compile 'com.sksamuel.elastic4s:elastic4s_2.11:1.5.10'

For SBT users simply add:

libraryDependencies += "com.sksamuel.elastic4s" %% "elastic4s" % "1.5.10"

For Maven users simply add (replace 2.11 with 2.10 for Scala 2.10):

<dependency>
    <groupId>com.sksamuel.elastic4s</groupId>
    <artifactId>elastic4s_2.11</artifactId>
    <version>1.5.10</version>
</dependency>

The above is just an example and is not always up to date. Check the latest released version on maven central

Building and Testing

This project is built with SBT. So to build

sbt compile

And to test

sbt test

Integration tests run on a local elastic that is created and torn down as part of the tests inside your standard temp folder. There is no need to configure anything externally.

Contributions

Contributions to elastic4s are always welcome. Good ways to contribute include:

Raising bugs and feature requests
Fixing bugs and enhancing the DSL
Improving the performance of elastic4s
Adding to the documentation

License

This software is licensed under the Apache 2 license, quoted below.

Copyright 2013-2014 Stephen Samuel

Licensed under the Apache License, Version 2.0 (the "License"); you may not
use this file except in compliance with the License. You may obtain a copy of
the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
License for the specific language governing permissions and limitations under
the License.

gregsilin / elastic4s