Elasticsearch client for C++: elasticlient and complete guide

Elasticsearch client for C++: complete guide to elasticlient

Elasticsearch is a powerful distributed search engine built on Apache Lucene. To interact with it from C++, there are several libraries. In this article, we will take a detailed look at elasticlient — a lightweight, modern, and convenient client that uses the libcurl library for HTTP requests and nlohmann/json for working with JSON. It is ideal for embedding search functions into native applications, server components, and data analysis tools.

Key features of elasticlient

• Support for all basic Elasticsearch operations: indexing, updating, deleting documents.
• Executing search queries with full text, filters, and aggregations.
• Index management: creating, deleting, configuring mappings.
• Bulk processing for high performance.
• Support for SSL/TLS and basic authentication.
• Asynchronous requests via callback mechanisms.

Installing the library

To build elasticlient, you will need a compiler with C++17 support and installed dependencies: libcurl (development) and nlohmann-json. Installation via package manager (Ubuntu/Debian):

sudo apt install libcurl4-openssl-dev nlohmann-json3-dev cmake g++

Building from source:

git clone https://github.com/elastic/elasticlient.gitcd elasticlientmkdir build && cd buildcmake .. -DCMAKE_BUILD_TYPE=Releasemake -j4sudo make install

Basic connection and configuration

To get started, create a client instance by specifying the URL of your Elasticsearch cluster:

#include <elasticlient/client.h>#include <iostream>

int main() {    elasticlient::Client client({"http://localhost:9200"});    // Connection check    auto ping = client.ping();    if (ping.status() == 200) {        std::cout << "Connection established!" << std::endl;    }    return 0;}

For a cluster with multiple nodes, pass a list of URLs:

elasticlient::Client client({    "http://node1:9200",    "http://node2:9200",    "http://node3:9200"});

Working with documents

Indexing a new document (create or update):

#include <nlohmann/json.hpp>using json = nlohmann::json;

json doc = {    {"title", "Elasticsearch for C++"},    {"content", "Detailed guide on using the elasticlient client"},    {"tags", {"cpp", "elasticsearch", "search"}},    {"views", 0}};

auto result = client.index("articles", "article", doc.dump(), "1");if (result.status() == 201) {    std::cout << "Document created: " << result.body() << std::endl;}

Getting a document by ID:

auto getResult = client.get("articles", "article", "1");if (getResult.status() == 200) {    json docJson = json::parse(getResult.body());    std::cout << "Title: " << docJson["_source"]["title"] << std::endl;}

Updating an existing document (partial):

json updateFields = {    {"doc", {{"views", 42}}}};auto updateResult = client.update("articles", "article", "1", updateFields.dump());

Search and filtering

Performing a full-text search using Query DSL:

json searchQuery = {    {"query", {        {"bool", {            {"must", {                {{"match", {{"content", "guide"}}}}            }},            {"filter", {                {{"term", {{"tags", "cpp"}}}}            }}        }}    }},    {"size", 10}};

auto searchResult = client.search("articles", searchQuery.dump());if (searchResult.status() == 200) {    json