Elasticsearch is a search server based on Lucene. It
provides a distributed, multitenant-capable
full-text search engine with a RESTful web interface and schema-free JSON
documents. Elasticsearch is developed in Java and is released
as open source under the terms of the Apache License.
To understand Elasticsearch, try the
following link : ElasticSearch
In this blog, I will try to explain how we can
use Elasticsearch in .net using NEST.
I have created the same application using visual studio 2013. You can download it from here.
Nest is a high level client that provides a
strongly typed query DSL that maps one-to-one with the Elasitcsearch query DSL,
and takes advantage of specific .NET features such as co-variant results. NEST internally uses, and still exposes, the low level Elasticsearch.Net client.
Elasticsearch provides API’s to build index
and to implement text search.
Why we need to use Elasticsearch:
Just have a look over the below mentioned SQL
Query.
In the above example, I am trying to join 4
tables in order to fetch required data. Meanwhile we need to take care of not
having duplicate rows in the result. Let’s assume that table has around 10,000
rows and then this query will definitely hits the performance of the
application. So it’s better to execute these queries and pull the results
before hand and index these documents once. Later while searching, search over
these index files and let the SQL to handle other operations. For more information watch this video.
Set Up:
- Download the latest version of
Elasticsearch from here.
- Unzip it and copy it to local
folder.
- Now we need to set JAVA_HOME
variable.
- In C drive, within program
files folder there will be a JAVA folder and within that folder jre
folder.
- Open that folder and copy the
folder path.
- Now open the command prompt and
type as mentioned below
set JAVA_HOME=paste the folder path you
copied earlier
- Then press enter. It will set
the JAVA_HOME variable.
- Now in command prompt, redirect
to the unzipped Elasticsearch bin folder.
- After redirecting, type in command
prompt as mentioned below
elasticseach
- Then press Enter.
- This will activate the
Elasticsearch.
- If everything goes right, you
will get something like as shown in below image
- To check, elasticsearch is
working properly, just open "http://localhost:9200/"
in browser. You will get the following result as follows
{
"status" : 200,
"name" : "Scarlet Scarab",
"cluster_name" : "elasticsearch",
"version" : {
"number" : "1.6.0",
"build_hash" :
"cdd3ac4dde4f69524ec0a14de3828cb95bbb86d0",
"build_timestamp" : "2015-06-09T13:36:34Z",
"build_snapshot" : false,
"lucene_version" : "4.10.4"
},
"tagline" : "You Know, for
Search"
}
- Now open visual studio and open
a console application.
- Install NEST using package manager
console using following code
PM> Install-Package NEST
Now your application has a reference to Elasticsearch.
Let’s jump into coding
stuff.
Class:
public class SearchBook
{
public int BookId { get; set; }
public string BookTitle { get; set; }
public string BookAuthor { get; set; }
}
First add Namespaces required:
using Nest;
Code:
var node = new
Uri("http://localhost:9200");
//” http://localhost:9200”---server
where Elasticsearch instance is hosted
var settings = new
ConnectionSettings( node, defaultIndex: "my-application");
//
defaultIndex- Is by default and we can change it to our specification later
while creating index.
var
client = new ElasticClient(settings);
Above code is common while creating, updating
and deleting the index. I will explain one by one.
Create Index: Let’s
create an index for an object.
SearchBook objSearchBook = new SearchBook();
//Load
the class object, you can load your object with data from sql or any other db
objSearchBook.BookId = 1;
objSearchBook.BookTitle = "Fantastic";
objSearchBook.BookAuthor = "Sam";
//
Create Index -- Index is generated with book id as a primary key
var CreateIndexResponse= client.Index(objSearchBook,i=> i.Index("index").Type("search").Id(objSearchBook.BookId));
NOTE: Before
running this code make sure that the “ElasticSearch” service is running, which
I did it using command prompt (Don’t close the prompt).
After executing last line you will get
the response in “CreateIndexResponse”. And the result is as shown below:
In
the response, you can check the “Created” value is “True”, it means the index
generated successfully. Huh! You did it….
Search: Let’s search the book details based on id and author
name.
var searchResults = client.Search<SearchBook>(s => s.Index("index").Type("search").From(0).Size(10).Query(q => q.Term(p
=> p.BookId, 1)));
NOTE: Before
running this code make sure that the “ElasticSearch” service is running, which
I did it using command prompt (Don’t close the prompt).
After executing the above line of code, you can see the
result in “searchResults”
as shown below image:
Search
Based On Book ID:
string
searchString = "sam";
var SearchBkByBookId =
client.Search<SearchBook>(s => s.Index("index").Type("search").From(0).Size(10).Query(q => q.Match(m => m.OnField(p => p. BookAuthor).Query(searchString))));
In the above query “searchString” is matched with only
BookAuthor column values, if you need to match the “searchString” with multiple
columns, you can use “OR” condition within “Match” query.
Note:
We can use “Term” or “Match” query, the problem with the
“Term” query which I used in the first search method is that query does not
analyze the search term. That’s why “Term” query are case sensitive.
The “Match” query uses the same analyzer which is used
while generating the index. Hence “Match” queries are not case sensitive. So
you use the proper query based on your search specifications.
“From()” and “Size()” is to limit your search result. It’s
like start and end point. Consider if we got 500 hits after searching for a text, and we
need only top 50 results the just mention “From(0)” and “Size(50)”.
There many other ways
to implement search, you can find them here.
Bulk Indexing:
When we have more records to index, we can use Bulk() API.
For trial purpose I am adding two objects to a class list. I hope you will get data from data source to the list.
SearchBook objSearchBook = new SearchBook();
List<SearchBook> lstSearchBook = new List<SearchBook>();
//Load the class object, you can load your object with data from sql or any other db
objSearchBook.BookId = 1;
objSearchBook.BookTitle = "Fantastic";
objSearchBook.BookAuthor = "Sam";
lstSearchBook.Add(objSearchBook);
objSearchBook = new SearchBook();
objSearchBook.BookId = 2;
objSearchBook.BookTitle = "Great";
objSearchBook.BookAuthor = "Sunny";
lstSearchBook.Add(objSearchBook);
// Bulk Index Generation-- We will index the lstSearchBook list objects.
var descriptor = new BulkDescriptor();
foreach (SearchBook book in lstSearchBook)
{
descriptor.Index<SearchBook>(op => op.Index("index").Type("searchbooks").Document(book));
}
var BulkIndex = client.Bulk(descriptor);
After executing the last line, you will get the response in "BulkIndex" as shown below:
I hope my post helps you to understand and implementing Elasticsearch in your application.
