Wrong indexation elasticsearch using the analyser - elasticsearch

Question

I did a pretty simple test. I build a student index and a type, then I define a mapping:
POST student
{
"mappings" : {
"ing3" : {
"properties" : {
"quote": {
"type": "string",
"analyzer": "english"
}
}
}
}
}
After that I add 3 students to this index:
POST /student/ing3/1
{
"name": "Smith",
"first_name" : "John",
"quote" : "Learning is so cool!!"
}
POST /student/ing3/2
{
"name": "Roosevelt",
"first_name" : "Franklin",
"quote" : "I learn everyday"
}
POST /student/ing3/3
{
"name": "Black",
"first_name" : "Mike",
"quote" : "I learned a lot at school"
}
At this point I thought that the english tokeniser will tokenise all the word in my quotes so if I'm making a search like:
GET /etudiant/ing3/_search
{
"query" : {
"term" : { "quote" : "learn" }
}
}
I will have all the document as a result since my tokeniser will make equal "learn, learning, learned" and I was right. But when I try this request:
GET /student/ing3/_search
{
"query" : {
"term" : { "quote" : "learned" }
}
}
I got zero hit and in my opinion I should have the 3rd document (at least?). But for me Elasticsearch is also supposed to index learned and learning not only learn. Am I wrong? Is my request wrong?

Answer 1

If you check:
GET 'index/_analyze?field=quote' -d "I learned a lot at school"
you will see that your sentence is analyzed as:
{
"tokens":[
{
"token":"i",
"start_offset":0,
"end_offset":1,
"type":"<ALPHANUM>",
"position":0
},
{
"token":"learn",
"start_offset":2,
"end_offset":9,
"type":"<ALPHANUM>",
"position":1
},
{
"token":"lot",
"start_offset":12,
"end_offset":15,
"type":"<ALPHANUM>",
"position":3
},
{
"token":"school",
"start_offset":19,
"end_offset":25,
"type":"<ALPHANUM>",
"position":5
}
]
}
So english analyzer removes punctions and stop words and tokenize words in their root form.
https://www.elastic.co/guide/en/elasticsearch/guide/current/using-language-analyzers.html
You can use match query which will also analyze your search text so will match:
GET /etudiant/ing3/_search
{
"query" : {
"match" : { "quote" : "learned" }
}
}

Answer 2

There is another way. You can both stem the terms (the english analyzer does have a stemmer), but also keep the original terms, by using a keyword_repeat token filter and then using a unique token filter with "only_on_same_position": true to remove unnecessary duplicates after the stemming:
PUT student
{
"settings": {
"analysis": {
"analyzer": {
"myAnalyzer": {
"type": "custom",
"tokenizer": "standard",
"filter": [
"english_possessive_stemmer",
"lowercase",
"english_stop",
"keyword_repeat",
"english_stemmer",
"unique_stem"
]
}
},
"filter": {
"unique_stem": {
"type": "unique",
"only_on_same_position": true
},
"english_stop": {
"type": "stop",
"stopwords": "_english_"
},
"english_stemmer": {
"type": "stemmer",
"language": "english"
},
"english_possessive_stemmer": {
"type": "stemmer",
"language": "possessive_english"
}
}
}
},
"mappings": {
"ing3": {
"properties": {
"quote": {
"type": "string",
"analyzer": "myAnalyzer"
}
}
}
}
}
In this case the term query will work, as well. If you look at what terms are actually being indexed:
GET /student/_search
{
"fielddata_fields": ["quote"]
}
it will be clear why now it matches:
"hits": [
{
"_index": "student",
"_type": "ing3",
"_id": "2",
"_score": 1,
"_source": {
"name": "Roosevelt",
"first_name": "Franklin",
"quote": "I learn everyday"
},
"fields": {
"quote": [
"everydai",
"everyday",
"i",
"learn"
]
}
},
{
"_index": "student",
"_type": "ing3",
"_id": "1",
"_score": 1,
"_source": {
"name": "Smith",
"first_name": "John",
"quote": "Learning is so cool!!"
},
"fields": {
"quote": [
"cool",
"learn",
"learning",
"so"
]
}
},
{
"_index": "student",
"_type": "ing3",
"_id": "3",
"_score": 1,
"_source": {
"name": "Black",
"first_name": "Mike",
"quote": "I learned a lot at school"
},
"fields": {
"quote": [
"i",
"learn",
"learned",
"lot",
"school"
]
}
}
]