add search features to your application - try elastic

5/20/2018 Add Search Features to Your Application - Try Elastic

Add search features to your application, try Elasticsearchpart 1 : theconcepts

bylouis gueye

Hi all,

The ultimate goal of a search engine is to provide fast, reliable, easy to use, scalable search features to a software.

But before diving into complex and technical considerations we should ask ourselves why bother with a search

engine.

1Why should my team bother with a new complex component ?

Adding a new component needs new dev/integration/ops skills. The learning curve might be important. The

configuration in testing mode can really be a nightmare to setup. So why introducing such risk and complexity

in a project ?

One day or another, anyone familiar with databases did add some contains semantics to search features.You

end up writing such queries:

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select*fromtable0 t0leftjointable1 t1 ont0.fk= t1.idleftjointable2 t2 ont1.fk= t2.id

leftjointable3 t3 ont2.fk= t3.idwheret0.title = '%term%'ort1.description = '%term%'andt3.created > '2011-01-12'andt3.status notin('archived', 'suspended', 'canceled')

The above query will perform slower and slower as your amount of data grows because the time consuming parts

of the query dont use the optimized path: indices. Moreover, as the requirements evolve, building your query

will be more of a nightmare than pleasure.

As a rule of thumb, whenever the time spent waiting for results in a complex search is not acceptable youre left

with 2 choices:

optimize your request: make sure you use the most optimized path,

use a search engine: highly optimized for reading and searching because it indexes almost everything (not true

for database which emphasizes on relations and structure).

2How does it work ?

The principle of a full-text search engine is based on indexing documents. First index documents then search in

those documents.

A document is a succession of words stored in sections/paragraphs. An analogy with database could be : a table
http://deepintojee.wordpress.com/author/deepintojee/http://t0.fk/http://t0.fk/http://t0.fk/http://t1.id/http://t1.id/http://t1.fk/http://t1.fk/http://t1.fk/http://t2.id/http://t2.id/http://t2.fk/http://t2.fk/http://t2.fk/http://t3.id/http://t3.id/http://t3.id/http://t2.fk/http://t2.id/http://t1.fk/http://t1.id/http://t0.fk/http://deepintojee.wordpress.com/author/deepintojee/


for a document, a field for a section. Words are tokens.

Indexing is the process of analysing a document and storing the result of that analysis for further retrieval.

Analysing is the process of extracting tokens from a field, counting occurences (which are valuable for

pertinence), associating them with unique path in document.

Not all tokens are relevant to search, some are so common that they are ignored. Indexers user analyzers that can

ignore such tokens.

Not all fields are analyzed. For instance a unique reference like ISBN should not be analyzed.

All the settings can be configured in a mapping.

You can search in the same type of document or in all type of documents. The later use case, though less

intuitive, can be a great time saver when it comes to build cross cutting informations like statistics.

Keep in mind : first write a document definition, setup your engine with that definition, index documents

(tokenize, store) then search.

3Which tool does the job ?

So far so good, I understand the concepts but dont know which tool does the job.

Before choosing a tool, to avoid getting lost in a world were not familiar with, lets write down requirements.

the tool should integrate seamlessly with either java or http (because HTTP is a great interface).

the tool should be easy to install : debian package would be awesome.

the tool should be easy to configure : declarative settings would be much appreciated.

the tool should provide a comprehensive documentation that allow one to get familiar with the concept first

then the practice.

the tool should provide a comprehensive integration/acceptance test suite that will serve as a learning tool.

the obvious ones : fast at runtime and lowest possible memory footprint.

While you haveWooshin python andZend Lucenein php, you haveSolr,ElasticsearchandHibernate Searchin

java.

They all rely on Lucene, are written in java and 2 of them (Elasticsearchand solr) offer HTTP interface to index

and search. Lucene is a very advanced and mature project. The amount of work around it is huge. But Lucene

mainly focuses on the very technical details about parsing and analysing text. It focuses on providing fast

searcher and reliable indexer and low level features like custom analysers, synonyms and all the plumbing/noise

that avoid one to focus on the business search requirements. The other projects take advantage of that core and

offer higher level features around it like remoting (REST/HTTP), declarative configuration, scaling (clusters,

etc), etc.

I did go forElasticsearchbecause it offers in-memory nodes which are valuable when testing in embedded mode.

In addition, REST is the preferred way to instrumentElasticsearch.I really like the idea because I believe that
http://packages.python.org/Whooshhttp://packages.python.org/Whooshhttp://packages.python.org/Whooshhttp://framework.zend.com/manual/en/zend.search.lucene.index-creation.htmlhttp://framework.zend.com/manual/en/zend.search.lucene.index-creation.htmlhttp://framework.zend.com/manual/en/zend.search.lucene.index-creation.htmlhttp://lucene.apache.org/solr/http://lucene.apache.org/solr/http://lucene.apache.org/solr/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://docs.jboss.org/hibernate/stable/search/reference/en-US/html/http://docs.jboss.org/hibernate/stable/search/reference/en-US/html/http://docs.jboss.org/hibernate/stable/search/reference/en-US/html/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://docs.jboss.org/hibernate/stable/search/reference/en-US/html/http://www.elasticsearch.org/http://lucene.apache.org/solr/http://framework.zend.com/manual/en/zend.search.lucene.index-creation.htmlhttp://packages.python.org/Whoosh


HTTP is a hell of an interface. Moreover the REST API is really simpler than the .

I cant do a comparative work, I can just explain why I was attracted byElasticsearch.

I think were good for the concepts. This article is the first in a series of 4Add search features to your

application, try Elasticsearch.

This is the full program:

part 1 :the concepts

part 2 :start small

part 3 :attaching indexation to events

part 4 :search(define a query grammar, parse query, build Elasticsearch query, search, build response)

Add search features to your application, tryElasticsearch part 2 : startsmall

Jan21bylouis gueye

Hi,

This article is part of a whole which aims to describe how one could integrateElasticsearch.Thepreviouspost

discussed the concepts: why using a search engine?.

No people learn the same way. I usually need to understand the theory and I need to start small.

So I usually start by books. If there is no book I look for a blog that explains the philosophy. Finally I look for

pieces of codes (official documentation, blogs, tutorials, github, etc). Starting small makes me confident and

allows me to increase complexity gradually.

Depending on what you want to know aboutElasticsearchyou should read different section of theguide:

-SETUPsection : describes how to install and run Elasticsearch (run as a service).

API: this is the REST API which seems more complete than the others. Describes how to inter-operate with

nodes : search, index, check clusters status.

Query DSL: the query API is quite rich. You have explanations about the syntax and semantics of queries and

filters.

Mapping: mapping configures elasticsearch when indexing/searching on a particular type of document.

Mapping is an important part which deserves special care.

Modules: presents the technical architecture with low level services like discovery or http.

Index modules: low level configuration on indices like sharding and logging.
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River: the river concept is the ability to feed your index from another datasource (pull data every X ms).

JavaandgroovyAPI : if your software already runs in a jvm you can benefit from that and control elastic

search via this API.

To avoid getting lost in the documentation, lets focus on simple goals. Well implement them progressively:

create node/client in test environment

create node/client in non test environment

integrate with Spring

create/delete/exists an index on a node

wait until node status is ok before operating on it

create/update/delete/find data on an index

create a mapping

1Admin operations

Operations on indices are admin operation. You can find them in the API section under Indices.

* Create node/client in test environment

A nodeis a process (a member) belonging to a cluster (a group). A builder is responsible of joining, detaching,

configuring the node. When creating a node, sensible defaults are already configured. I didntdive into the

discovery process and I wont. Creating a node will automatically create its encapsulating cluster. Creating a node

is as simple as :

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// settingsprivateSettings defaultSettings = ImmutableSettings.settingsBuilder().put("cluster.name",NetworkUtils.getLocalAddress().getHostName()).build(); // create nodefinalNode node = NodeBuilder.nodeBuilder().local(true).data(true).settings(defaultSetting// start nodenode.start()

The above code will create a node instance. The node doesnt use the transport layer (tcp). So no rmi, no http, no

network services. Everything happens in the jvm.

To operate with a node you must acquire a client from your node. Any single operation depends

on it

1 Client client = node.client();

An invaluable resource on how to setup nodes and clients in test env is theAbstractNodesTestsclass.

* Create node in non test environment

In non test env just install Elasticsearch like described in the documentationSETUPsection.This installation

uses the transport layer (tcp).
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There isnt an official debian package butNicolas HurayandDamien Hardycontributed on the project and

wrote one which has will be integrated to the 0.19 branch. This branch moves from a gradle building system to

maven. It will use the jdeb-maven-plugin to build the debian package. It will then be available for download on

the elasticsearch site.

Once installed you should have anElasticsearchinstance up and running with a discovery service listening on

port 54328, an HTTP service listening on 9200and an inter-node communication port 9300.

The default cluster name is elasticsearch but we do no use it to make sure tests run in isolation.

For more onnodesandclustersconfiguration feel free to read this page in the official documentation.

* Integrate with Spring

You can integrate with spring by creating a FactoryBeanwich is responsible for the Node/Client construction.

Dont forget todestroythem as they really are memory consuming (beware of PermGenSpace ).

Thispost,though a bit complex for my needs, was helpful.

If interested in that specific part you can take a look atLocalNodeClientFactoryBean.

* Create an index on a node

Once your node is up you can create indices. The main property of the index is its name which acts like an id. A

node canthave 2 indices with same name. The index name cant contains special chars like ., / etc. Keep it

simple.

1 Client client = node.client();

Then create an index with adverts id, intended to store adverts :

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client.admin().indices().prepareCreate("adverts") .execute().actionGet();

Depending on your organization you can choose to create one indice per software or one indice per stored type or

wathever settings suits you. You just have to maintain the indices names.

* Remove an index from a node

As soon as you have the name it is straightforward. You should can test existence before removing.

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if(client.admin().indices().prepareExists("adverts") .execute().actionGet().exists()) {

client.admin().indices().prepareDelete("adverts") .execute().actionGet();

}

* Wait for cluster health

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client.admin().cluster() .prepareHealth("adverts").setWaitForYellowStatus() .execute().actionGet();
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2Data operations

* Create / Update

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client.prepareIndex("adverts", "advert", "1286743")//.setRefresh(true) //.setSource(advertToJsonByteArrayConverter.convert(advert)) //.execute().actionGet();

The above code will index data (the source) whose type is advert under the adverts index area. It will also

commit (refresh) the index modifications.

The source can be many types ranging from a fieldName/value map to the byte array. The byte array is the

preferred way so I created converters from/to byte[]/Advert.

AdvertToJsonByteArrayConverter (relies on Spring Converter interface)

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...

/*** @see org.springframework.core.convert.converter.Converter#convert(java.lang.Objec

*/@Overridepublicbyte[] convert(finalAdvert source) {

if(source == null) returnnull;

this.jsonMapper.getSerializationConfig() .without(SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS);

String string;try{

string = this.jsonMapper.writeValueAsString(source);returnstring.getBytes("utf-8"); } catch(finalThrowable th) {

thrownewIllegalArgumentException(th); }// System.out.println("source as string = " + string);

}

...

Updating means re-indexing so its the exact same operation.

* Delete data

When done with an object and we dont want it to appear in search results we might want to delete it from the

index:

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client.prepareDelete("adverts", "advert", "4586321").setRefresh(true).execute().actionGet();

That will delete then refresh immediately after.

* Find data


The search API is very rich so you have to understand search semantics. If youre familiar with lucenethen

everything will seem obvious to you. But if you dont youll have to get familiar with the basics.

There are 2 main types of search : exact match and full text.

The exact matchoperates on fields as a whole data. The field is considered a term (even if it contains spaces). It

is not analyzed, so querying field=condition will return nothing if field equals excellent condition. Exact

match suits very well for certain fields (id, reference, date, status, etc) but not for all. Exact match fields can be

sorted.

The full textoperates on tokens. The analyzer removes stop words, splits the field in tokens, groups them. The

most relevant result is the one that contains the higher term occurences (roughly).

You obviously cant apply a lexical sort on those fields. They are sorted by score.

Below, an exact match example (will match adverts with provided id):

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privateSearchResponse findById(finalLong id) {returnclient.prepareSearch("adverts").setTypes("advert")

.setQuery(QueryBuilders.boolQuery()

.must(QueryBuilders.termQuery("_id", id))).execute().actionGet();}

Below, a full text on a single field example (will match adverts whose description field contains at least once the

term condition):

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client.prepareSearch("adverts").setTypes("advert")

.setQuery(QueryBuilders.boolQuery()

.must(QueryBuilders.queryString("condition")

.defaultField("description")).execute().actionGet();

* Create a mapping

The searchable nature of a fieldis an important design decision and can be configured in the mapping. It

defines, for an indexed type, the indexed fields and for each field some interesting propertieslike analyzed

nature(analyze|not_analyzed), type(long, string, date) , etc.Elasticsearchprovides a default mapping: strings

fields are analyzed, other ones are not.I really recommend you to spend some time on thatsection.One dont necessarily have to design the perfect

mapping the first time (it requires some experience) but the decisions taken on that part will impact the search

results.

Below an example of mapping:

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{"advert": {

"properties" : {

"id": {"type": "long","index": "not_analyzed"

},"name": {

"type": "string"
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},"description": {

"type": "string"},"email": {

"type": "string","index": "not_analyzed"

},"phoneNumber": {

"type": "string",

"index": "not_analyzed"},"reference": {

"type": "string","index": "not_analyzed"

},"address": {

"dynamic": "true","properties" : {

"streetAddress" : {"type": "string"

},"postalCode": {

"type": "string"},"city": {

"type": "string"},"countryCode" : {

"type": "string"}

}}

}}

}

I gathered those CRUD operations in 2 integration tests

:ElasticSearchDataOperationsTestITandElasticSearchAdminOperationsTestIT.

Now that were familiar with Elasticsearch basic operations we can move on. We can consider improving the

code.

You agree that handling the indexing task manually is an option but not the most elegant and reliable one.

In thenext postwell discuss the different solutions to automatically index our data.

Add search features to your application, tryElasticsearch part 3 : attaching indexationtoevents

Jan22bylouis gueye

Now that we are able to index, we should think ofwhenwhe should triggerindexing tasks.
https://github.com/lgueye/jbehave-poc/blob/master/src/test/java/org/diveintojee/poc/jbehave/persistence/ElasticSearchDataOperationsTestIT.javahttps://github.com/lgueye/jbehave-poc/blob/master/src/test/java/org/diveintojee/poc/jbehave/persistence/ElasticSearchDataOperationsTestIT.javahttps://github.com/lgueye/jbehave-poc/blob/master/src/test/java/org/diveintojee/poc/jbehave/persistence/ElasticSearchAdminOperationsTestIT.javahttps://github.com/lgueye/jbehave-poc/blob/master/src/test/java/org/diveintojee/poc/jbehave/persistence/ElasticSearchAdminOperationsTestIT.javahttps://github.com/lgueye/jbehave-poc/blob/master/src/test/java/org/diveintojee/poc/jbehave/persistence/ElasticSearchAdminOperationsTestIT.javahttp://deepintojee.wordpress.com/2012/01/22/add-search-features-to-your-application-try-elasticsearch-part-3-attaching-indexation-to-events/http://deepintojee.wordpress.com/2012/01/22/add-search-features-to-your-application-try-elasticsearch-part-3-attaching-indexation-to-events/http://deepintojee.wordpress.com/2012/01/22/add-search-features-to-your-application-try-elasticsearch-part-3-attaching-indexation-to-events/http://deepintojee.wordpress.com/2012/01/22/add-search-features-to-your-application-try-elasticsearch-part-3-attaching-indexation-to-events/http://deepintojee.wordpress.com/2012/01/22/add-search-features-to-your-application-try-elasticsearch-part-3-attaching-indexation-to-events/http://deepintojee.wordpress.com/author/deepintojee/http://deepintojee.wordpress.com/author/deepintojee/http://deepintojee.wordpress.com/2012/01/22/add-search-features-to-your-application-try-elasticsearch-part-3-attaching-indexation-to-events/http://deepintojee.wordpress.com/2012/01/22/add-search-features-to-your-application-try-elasticsearch-part-3-attaching-indexation-to-events/https://github.com/lgueye/jbehave-poc/blob/master/src/test/java/org/diveintojee/poc/jbehave/persistence/ElasticSearchAdminOperationsTestIT.javahttps://github.com/lgueye/jbehave-poc/blob/master/src/test/java/org/diveintojee/poc/jbehave/persistence/ElasticSearchDataOperationsTestIT.java


A simple answer would be : whenever some indexed data has changed. Changed means change cardinality

(add/remove) or change existing data.

Either we invoke indexing tasks whenever we code an action that changes data or we use an event model which

listens to precise events.

1JPA event model

If you useJPAas a persistence mechanism you can take advantage of its elegant mechanism. You can register an

entitys listeners either at class level or at method level viaannotations.

One can annotate an entity method as a listner to an event. The method is the will be executed when the event

defined by the annotation occurs.

If this solution seems too intrusive or too specific, one can externalize this behaviour in a class and annotate the

entity.

Below, an example:

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importjavax.persistence.Entity; importjavax.persistence.EntityListeners; importjavax.persistence.Id;importjavax.persistence.PostLoad; importjavax.persistence.PostPersist; importjavax.persistence.PostUpdate; importjavax.persistence.PrePersist; importjavax.persistence.PreRemove; importjavax.persistence.PreUpdate; importjavax.persistence.Transient;

@Entity@EntityListeners({EmployeeDebugListener.class, NameValidator.class})publicclassEmployee {

@Idprivateintid;privateString name;@TransientprivatelongsyncTime;

@PostPersist@PostUpdate@PostLoad

privatevoidresetSyncTime() {syncTime = System.currentTimeMillis();System.out.println("Employee.resetSyncTime called on employee id: "+ getId());

}

publiclonggetCachedAge() {returnSystem.currentTimeMillis() - syncTime;

}

publicintgetId() {returnid;

}

publicvoid

setId(int

id) {

this.id = id;}

publicString toString() {return"Employee id: "+ getId() ;
http://en.wikipedia.org/wiki/Java_Persistence_APIhttp://en.wikipedia.org/wiki/Java_Persistence_APIhttp://en.wikipedia.org/wiki/Java_Persistence_APIhttp://javax.persistence.id/http://javax.persistence.id/http://javax.persistence.id/http://en.wikipedia.org/wiki/Java_Persistence_API


}}

That model, although very elegant, doesnt suit you if you useSpringbecause the persistence cant use a bean

instance. It creates its own instances which totally goes against dependency injection.This postis a rather

complete material about the solution based onJPA.

2Hibernate event model

When usingHibernate,withoutJPA,withSpringyou can register instances, not only classes. Your

application can listen to post-insert/post-update/post-delete events. This solution is my favorite one if your

application writes little and reads much.

You can specify your listeners by setting the eventListeners propertyof theLocalSessionFactoryBean.Its a

map which associates an event key to an array of listeners instance.

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searchEngine.removeFromIndex(id); }

}...

This is one of the most non intrusive solution. It also ensures that even if you add a new business method that

updates the database state, changes will automatically reflect in the index. No need to manually call index tasks.

3Spring event model

When youre stuck withJPAyou can useSpringevent model. You useApplicationEventPublisherto publish

CRUD event then implementApplicationListenerto react to the event.

Parameterized types (generics) ensure your code will react to one type only, this can be quite convenient: not

reacting to Job event but reacting to Advert events.

That solution is not very resistant to changes because if you forget to trigger an event nothing will happen. It is

equivalent to manually call index taks but it is the only one available when usingJPA.

Example ofApplicationEventPublishercall:

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...@AutowiredprivateApplicationEventPublisher eventPublisher;/*** @see org.diveintojee.poc.jbehave.domain.business.Facade#deleteAdvert(java.lang.Lo

*/@Override@Transactional(propagation = Propagation.REQUIRED)publicvoiddeleteAdvert(final Long advertId) {

Preconditions.checkArgument(advertId != null,"Illegal call to deleteAdvert, advert identifier is required");

this.baseDao.delete(Advert.class, advertId);this.eventPublisher.publishEvent(new PostDeleteAdvertEvent(new Advert(advertId)));

}...

Example of event listener:

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.../*** @[email protected]

*/@ComponentpublicclassPostDeleteAdvertEventListener implementsApplicationListener


4Elasticsearch river

AnElasticsearchRiveris a mechanism which pulls data from a datasource(couchdb, twitter, wikipedia,

rabbitmq, rss) on a regular basis (500 ms for example) and updates the index based on what changed since the

last refresh. The idea is really nice but there a too few plugin yet.Elasticsearchprovides only 4 rivers plugin but

contributions are more than welcome :).

So far weve got familiar with search engineconceptsthen we started to have a first contact

withElasticsearchwritingCRUDtests.

We just discussed several solutions to trigger indexing. Now that we know how to index data we can finally focus

on the search business which is what thenext postwill try to present.

The source code hasnt moved, still on github. Feel free toexploreit

Add search features to your application, tryElasticsearch part 4 :search

Jan23bylouis gueye

Elasticsearchrelies onLuceneengine.

The good news is thatLuceneis really fast and powerful. Yet, its not a good idea toexpose such powerto the

user.Elasticsearchacts as a first filter but remains quite complete.

When you dont master an API, a good practice is tohave controlover what you expose to the user. But this

comes with a cost, youll have to:

implement a query language

implement a language parser

implement a query translator (translate into something understandable by elasticsearch)run search

translateElasticsearchresults into a custom structure

The task seems daunting but no worry: were going to take a look at each step.

1The query language

Once youve delimit the perimeter, its simpler. I imagined something like:

1http://domain/search/adverts?query=reference:REF-TTTT111gg4!description~condition legal!c2009&from=2&itemsPerPage=10&sort=created+desc
http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/guide/reference/river/http://www.elasticsearch.org/guide/reference/river/http://www.elasticsearch.org/guide/reference/river/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://deepintojee.wordpress.com/2012/01/20/add-search-features-to-your-application-try-elasticsearch-part-1-the-concepts/http://deepintojee.wordpress.com/2012/01/20/add-search-features-to-your-application-try-elasticsearch-part-1-the-concepts/http://deepintojee.wordpress.com/2012/01/20/add-search-features-to-your-application-try-elasticsearch-part-1-the-concepts/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://deepintojee.wordpress.com/2012/01/21/add-search-features-to-your-application-try-elasticsearch-part-2-start-small/http://deepintojee.wordpress.com/2012/01/21/add-search-features-to-your-application-try-elasticsearch-part-2-start-small/http://deepintojee.wordpress.com/2012/01/21/add-search-features-to-your-application-try-elasticsearch-part-2-start-small/http://deepintojee.wordpress.com/2012/01/23/add-search-features-to-your-application-try-elasticsearch-part-4-search/http://deepintojee.wordpress.com/2012/01/23/add-search-features-to-your-application-try-elasticsearch-part-4-search/https://github.com/lgueye/jbehave-pochttps://github.com/lgueye/jbehave-pochttps://github.com/lgueye/jbehave-pochttp://deepintojee.wordpress.com/2012/01/23/add-search-features-to-your-application-try-elasticsearch-part-4-search/http://deepintojee.wordpress.com/2012/01/23/add-search-features-to-your-application-try-elasticsearch-part-4-search/http://deepintojee.wordpress.com/author/deepintojee/http://www.elasticsearch.org/http://www.elasticsearch.org/http://lucene.apache.org/http://lucene.apache.org/http://lucene.apache.org/http://lucene.apache.org/http://lucene.apache.org/http://lucene.apache.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://www.elasticsearch.org/http://lucene.apache.org/http://lucene.apache.org/http://www.elasticsearch.org/http://deepintojee.wordpress.com/author/deepintojee/http://deepintojee.wordpress.com/2012/01/23/add-search-features-to-your-application-try-elasticsearch-part-4-search/https://github.com/lgueye/jbehave-pochttp://deepintojee.wordpress.com/2012/01/23/add-search-features-to-your-application-try-elasticsearch-part-4-search/http://deepintojee.wordpress.com/2012/01/21/add-search-features-to-your-application-try-elasticsearch-part-2-start-small/http://www.elasticsearch.org/http://deepintojee.wordpress.com/2012/01/20/add-search-features-to-your-application-try-elasticsearch-part-1-the-concepts/http://www.elasticsearch.org/http://www.elasticsearch.org/guide/reference/river/http://www.elasticsearch.org/


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query := (Clause!)* ;Clause := (Field Operator Value)* | (Value)+ ;Field := ? fieldname without space ? ;Operator := (:|~|lt|gt|lte|gte) ;Value : ? anything form-url-encoded ? ;

The query param is optional, if not specified, the default search should return all elements.

The from param is optional, if not specified, the 1st page is assumed

The itemsPerPage is optional, if not specified, a page will contain 10 results

The sort param is optional, if not specified, the result will be sorted by id desc.

Well even so, it is not trivial. For the purpose of the poc I simplified my requirements:

I did not use a ENBF parser like ANTLR : parsers deserve their own post.

I did not implement all the operators.

Below, the piece of code used to split clauses:

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List extractSearchClauses(finalString queryString) {if(StringUtils.isEmpty(queryString)) returnnull;finalList clauses = Arrays.asList(queryString.split(CLAUSES_SEPARATOR));finalCollection cleanClauses = Collections2.filter(clauses, newPredicate() {

/*** @see com.google.common.base.Predicate#apply(java.lang.Object)*/

@Overridepublicbooleanapply(finalString input) {

returnStringUtils.isNotEmpty(input)// && !input.trim().equals(SearchOperator.EXACT_MATCH_OPERATOR.toString

&& !input.trim().equals(SearchOperator.FULL_TEXT_OPERATOR.toString() &&!input.trim().endsWith(SearchOperator.EXACT_MATCH_OPERATOR.toString())//

&& !input.trim().endsWith(SearchOperator.FULL_TEXT_OPERATOR.toString }

});

returnnewArrayList(cleanClauses);

}

2Translate to Elasticsearch language

First lets establish a few rules

an empty clauses list means returning all the elements (/adverts?)

a single clause that contains no field and no operator means a full text search on all searchable fields

(/adverts?q=condition+legal)

a multiple clause means a boolean AND query between clauses (/adverts?query=reference:REF-

TTTT111gg4!description~condition legal)

Elasticsearchcomes with a rich search API which encapsulates the query building in a collection

ofQueryBuilders.

Below an example of search instructions:
http://www.elasticsearch.org/http://www.elasticsearch.org/https://github.com/elasticsearch/elasticsearch/blob/master/src/main/java/org/elasticsearch/index/query/QueryBuilders.javahttps://github.com/elasticsearch/elasticsearch/blob/master/src/main/java/org/elasticsearch/index/query/QueryBuilders.javahttps://github.com/elasticsearch/elasticsearch/blob/master/src/main/java/org/elasticsearch/index/query/QueryBuilders.javahttps://github.com/elasticsearch/elasticsearch/blob/master/src/main/java/org/elasticsearch/index/query/QueryBuilders.javahttp://www.elasticsearch.org/


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...((BoolQueryBuilder) queryBuilder).must(queryString(clause.getValue())

.defaultField(clause.getField())); ...

3Running search

TheSearchRequestBuilderis an abstraction that encapsulates the well known search domain which specifies:

pagination properties (items per page, page number),

sort specification (fields, sort direction),

query (built by chainingQueryBuilders).

Once youve configured yourSearchRequestBuilderyou can run the actual search

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...finalSearchResponse searchResponse = searchRequestBuilder.execute().actionGet();...

4Transfer results to a custom structure

Ideally, we should return a search result that contains total hitsand pagination results(previous, next, first,

last). Those are the only information needed by the user.

But remember : the index stores a json byte array (not mandatory but I chose it because I build RESTful

services), not an object. We have to re-build our objectfrom JSON representation.

Again, writing aConverterreally helps.

I did not implement pagination as its another entire concern : building a RESTful search response thatrespectsHATEOASprinciples. Ill blog on that later.

Example ofConverterinvocation:

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...finalSearchResult result = this.searchResponseToSearchResultConverter.convert(searchResporeturnresult;...

And below theConvertersource (I could have used a transform function ):

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...publicSearchResult convert(finalSearchResponse source) {

finalSearchResult result = newSearchResult(); finalSearchHits hits = source.getHits();result.setTotalHits(hits.getTotalHits()); for(finalSearchHit searchHit : hits.getHits()) {

finalAdvert advert = jsonByteArrayToAdvertConverter.convert(searchHit.source result.addItem(advert);

}returnresult;

}...

This post closes a series of 4 on elasticsearch first contact.

We discussed theconcepts,but before designing anything we wanted toget familiar with our new tool.
https://github.com/elasticsearch/elasticsearch/blob/0.18/modules/elasticsearch/src/main/java/org/elasticsearch/client/action/search/SearchRequestBuilder.javahttps://github.com/elasticsearch/elasticsearch/blob/0.18/modules/elasticsearch/src/main/java/org/elasticsearch/client/action/search/SearchRequestBuilder.javahttps://github.com/elasticsearch/elasticsearch/blob/0.18/modules/elasticsearch/src/main/java/org/elasticsearch/client/action/search/SearchRequestBuilder.javahttps://github.com/elasticsearch/elasticsearch/blob/master/src/main/java/org/elasticsearch/index/query/QueryBuilders.javahttps://github.com/elasticsearch/elasticsearch/blob/master/src/main/java/org/elasticsearch/index/query/QueryBuilders.javahttps://github.com/elasticsearch/elasticsearch/blob/master/src/main/java/org/elasticsearch/index/query/QueryBuilders.javahttps://github.com/elasticsearch/elasticsearch/blob/0.18/modules/elasticsearch/src/main/java/org/elasticsearch/client/action/search/SearchRequestBuilder.javahttps://github.com/elasticsearch/elasticsearch/blob/0.18/modules/elasticsearch/src/main/java/org/elasticsearch/client/action/search/SearchRequestBuilder.javahttps://github.com/elasticsearch/elasticsearch/blob/0.18/modules/elasticsearch/src/main/java/org/elasticsearch/client/action/search/SearchRequestBuilder.javahttp://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttp://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttp://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttp://en.wikipedia.org/wiki/HATEOAShttp://en.wikipedia.org/wiki/HATEOAShttp://en.wikipedia.org/wiki/HATEOAShttp://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttp://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttp://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttp://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttp://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttp://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttp://deepintojee.wordpress.com/2012/01/20/add-search-features-to-your-application-try-elasticsearch-part-1-the-concepts/http://deepintojee.wordpress.com/2012/01/20/add-search-features-to-your-application-try-elasticsearch-part-1-the-concepts/http://deepintojee.wordpress.com/2012/01/20/add-search-features-to-your-application-try-elasticsearch-part-1-the-concepts/http://deepintojee.wordpress.com/2012/01/21/add-search-features-to-your-application-try-elasticsearch-part-2-start-small/http://deepintojee.wordpress.com/2012/01/21/add-search-features-to-your-application-try-elasticsearch-part-2-start-small/http://deepintojee.wordpress.com/2012/01/21/add-search-features-to-your-application-try-elasticsearch-part-2-start-small/http://deepintojee.wordpress.com/2012/01/21/add-search-features-to-your-application-try-elasticsearch-part-2-start-small/http://deepintojee.wordpress.com/2012/01/20/add-search-features-to-your-application-try-elasticsearch-part-1-the-concepts/http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttp://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttp://en.wikipedia.org/wiki/HATEOAShttp://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/core/convert/converter/Converter.htmlhttps://github.com/elasticsearch/elasticsearch/blob/0.18/modules/elasticsearch/src/main/java/org/elasticsearch/client/action/search/SearchRequestBuilder.javahttps://github.com/elasticsearch/elasticsearch/blob/master/src/main/java/org/elasticsearch/index/query/QueryBuilders.javahttps://github.com/elasticsearch/elasticsearch/blob/0.18/modules/elasticsearch/src/main/java/org/elasticsearch/client/action/search/SearchRequestBuilder.java


Once more comfortable withElasticsearch,we started serious work: attachingindexing tasks to application

eventsfirst, then building a simple search endpoint that uses Elasticsearch under the hood.

I cant say that I totally adopted the tool because there still is a lot to validate:

searches : I dont know all the specifics/semantics/differences between all the pre-definedQueryBuilders.

facets : how do they work inElasticsearch?

I always heard it is insanely fast with high volumes. I want to see it with my own eyes.

JPA was disappointing (not anElasticsearchproblem) : maybe I could use CDI

I still have to figure out how to cleanly setup different clients instanciation modes : memory and transport

clients. UsingSpring profilesis a solution but Im not a big fan of profiles

I wish I could test a mysql river. Id like to compare the river to the events mechanism.

I try not to be too exhalted but I have to say its a real pleasure once youve past the first pitfalls mostly related to:

node/client management: like jdbc connections,youre responsible for opening/closing your

resourcesotherwise you may have unexpected side effects,

mapping design: analysedand not_analysedproperties have a huge impact on your search,

and blindness: in memory testing is for experienced userwho already know the API. I would suggest a real

time-saver tool :Elasticsearch Head.This tool helped us understand how data was organized/stored, what data

was currently in the index, if it was correctly deleted, etc. The price to pay: only works with transport

configuration, not in-memory.

Anyway I hope you enjoyed the reading. If so feel free to share. If not, let me know why (I might have some

inacurate informations) as soon as we learn something.

The fullsourceis on github.

Run the following command to launchJbehavesearch stories

1 mvn clean verify -Psearch

Reference:

http://deepintojee.wordpress.com/2012/01/20/add-search-features-to-your-application-try-elasticsearch-part-1-the-concepts/

http://deepintojee.wordpress.com/2012/01/21/add-search-features-to-your-application-try-elasticsearch-part-2-start-small/

http://deepintojee.wordpress.com/2012/01/22/add-search-features-to-your-application-try-elasticsearch-part-3-attaching-indexation-to-events/

http://deepintojee.wordpress.com/2012/01/23/add-search-features-to-your-application-try-elasticsearch-part-4-search/
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csearch-part-3-attaching-indexation-to-events/http://www.elasticsearch.org/

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