I have populated an Elasticsearch database using the following settings:
mapping = {
"properties": {
"location": {
"type": "text",
"analyzer": "ngram_analyzer"
},
"description": {
"type": "text",
"analyzer": "ngram_analyzer"
},
"commentaar": {
"type": "text",
"analyzer": "ngram_analyzer"
},
}
}
settings = {
"settings": {
"analysis": {
"filter": {
"ngram_filter": {
"type": "ngram",
"min_gram": 1,
"max_gram": 20
}
},
"analyzer": {
"ngram_analyzer": {
"type": "custom",
"tokenizer": "whitespace",
"filter": [
"lowercase",
"ngram_filter"
]
}
}
}
},
"mappings": {"custom_tool": mapping}
}
I used the ngram analyser because I wanted the be able to have subword matching. So a search for "ackoverfl" would return the entries containing "stackoverflow".
My search queries are made as follows:
q = {
"simple_query_string": {
"query": needle,
"default_operator": "and",
"analyzer": "whitespace"
}
}
Where needle is the text from my search bar.
Sometimes I would also like to do literal phrase searching. For example:
If my search term is:
"the ap hangs in the tree"
(Notice that I use quotation marks here with the intention the search for a literal piece of text).
Then in my results I get a document containing:
the apple hangs in the tree
This results is unwanted.
How could I implement having a subword matching search capability while also having the option to search for literal phrases (by using for example quotation marks) ?
Related
Main question
The user is looking for a name and enters the part of the it, let's say au, and the document with the text paul is found.
I would like to have the doc highlighted like p<em>au</em>l.
How can I achieve it if I have a complex search query (combination of match, prefix, wildcard to rule relevance)?
Sub question
When do highlight settings from documentation for type, boundary_scanner and boundary_chars come into play? As per my tests described below, these settings don't change highlighted part.
Try 1: Wildcard query with default analyzer
PUT myindex
{
"mappings": {
"properties": {
"name": {
"type": "text",
"term_vector": "with_positions_offsets"
}
}
}
}
POST myindex/_doc/1
{
"name": "paul"
}
GET myindex/_search
{
"query": {
"wildcard": {"name": "*au*"}
},
"highlight": {
"fields": {
"name": {}
},
"type": "fvh",
"boundary_scanner": "chars",
"boundary_chars": "abcdefghijklmnopqrstuvwxyz.,!? \t\n"
}
}
This kind of search returns highlight <em>paul</em> but I need to get p<em>au</em>l.
Try 2: Match query with NGRAM analyzer
This one works as described in SO question: Highlighting part of word in elasticsearch
PUT myindexngram
{
"settings": {
"analysis": {
"tokenizer": {
"ngram_tokenizer": {
"type": "nGram",
"min_gram": "2",
"max_gram": "3",
"token_chars": [
"letter",
"digit"
]
}
},
"analyzer": {
"index_ngram_analyzer": {
"type": "custom",
"tokenizer": "ngram_tokenizer",
"filter": [
"lowercase"
]
},
"search_term_analyzer": {
"type": "custom",
"tokenizer": "keyword",
"filter": "lowercase"
}
}
}
},
"mappings": {
"properties": {
"name": {
"type": "text",
"analyzer": "index_ngram_analyzer",
"term_vector": "with_positions_offsets"
}
}
}
}
POST myindexngram/_doc/1
{
"name": "paul"
}
GET myindexngram/_search
{
"query": {
"match": {"name": "au"}
},
"highlight": {
"fields": {
"name": {}
}
}
}
This highlights p<em>au</em>l as desired but:
Highlighting depends on the query type, so combining match and wildcard will again result in <em>paul</em>.
Highlighting is not affected at all on type, boundary_scanner and boundary_chars settings.
Elastic version 7.13.4
Response from Elasticsearch team:
A highlighter works on terms, so only full terms can be highlighted - whatever are the terms in your index. In your second example, au could be highlighted, because it it a term in the index, which is not the case for your first example.
There is also an option to define your own highlight_query that could be different from the main query, but this could lead to unpredictable highlights.
https://discuss.elastic.co/t/configure-highlighted-part/295164
The Problem
I am working on an autocompleter using ElasticSearch 6.2.3. I would like my query results (a list of pages with a Name field) to be ordered using the following priority:
Prefix match at start of "Name" (Prefix query)
Any other exact (whole word) match within "Name" (Term query)
Fuzzy match (this is currently done on a different field to Name using a ngram tokenizer ... so I assume cannot be relevant to my problem but I would like to apply this on the Name field as well)
My Attempted Solution
I will be using a Bool/Should query consisting of three queries (corresponding to the three priorities above), using boost to define relative importance.
The issue I am having is with the Prefix query - it appears to not be lowercasing the search query despite my search analyzer having the lowercase filter. For example, the below query returns "Harry Potter" for 'harry' but returns zero results for 'Harry':
{ "query": { "prefix": { "Name.raw" : "Harry" } } }
I have verified using the _analyze API that both my analyzers do indeed lowercase the text "Harry" to "harry". Where am I going wrong?
From the ES documentation I understand I need to analyze the Name field in two different ways to enable use of both Prefix and Term queries:
using the "keyword" tokenizer to enable the Prefix query (I have applied this on a .raw field)
using a standard analyzer to enable the Term (I have applied this on the Name field)
I have checked duplicate questions such as this one but the answers have not helped
My mapping and settings are below
ES Index Mapping
{
"myIndex": {
"mappings": {
"pages": {
"properties": {
"Id": {},
"Name": {
"type": "text",
"fields": {
"raw": {
"type": "text",
"analyzer": "keywordAnalyzer",
"search_analyzer": "pageSearchAnalyzer"
}
},
"analyzer": "pageSearchAnalyzer"
},
"Tokens": {}, // Other fields not important for this question
}
}
}
}
}
ES Index Settings
{
"myIndex": {
"settings": {
"index": {
"analysis": {
"filter": {
"ngram": {
"type": "edgeNGram",
"min_gram": "2",
"max_gram": "15"
}
},
"analyzer": {
"keywordAnalyzer": {
"filter": [
"trim",
"lowercase",
"asciifolding"
],
"type": "custom",
"tokenizer": "keyword"
},
"pageSearchAnalyzer": {
"filter": [
"trim",
"lowercase",
"asciifolding"
],
"type": "custom",
"tokenizer": "standard"
},
"pageIndexAnalyzer": {
"filter": [
"trim",
"lowercase",
"asciifolding",
"ngram"
],
"type": "custom",
"tokenizer": "standard"
}
}
},
"number_of_replicas": "1",
"uuid": "l2AXoENGRqafm42OSWWTAg",
"version": {}
}
}
}
}
Prefix queries don't analyze the search terms, so the text you pass into it bypasses whatever would be used as the search analyzer (in your case, the configured search_analyzer: pageSearchAnalyzer) and evaluates Harry as-is directly against the keyword-tokenized, custom-filtered harry potter that was the result of the keywordAnalyzer applied at index time.
In your case here, you'll need to do one of a few different things:
Since you're using a lowercase filter on the field, you could just always use lowercase terms in your prefix query (using application-side lowercasing if necessary)
Run a match query against an edge_ngram-analyzed field instead of a prefix query like described in the ES search_analyzer docs
Here's an example of the latter:
1) Create the index w/ ngram analyzer and (recommended) standard search analyzer
PUT my_index
{
"settings": {
"index": {
"analysis": {
"filter": {
"ngram": {
"type": "edgeNGram",
"min_gram": "2",
"max_gram": "15"
}
},
"analyzer": {
"pageIndexAnalyzer": {
"filter": [
"trim",
"lowercase",
"asciifolding",
"ngram"
],
"type": "custom",
"tokenizer": "keyword"
}
}
}
}
},
"mappings": {
"pages": {
"properties": {
"name": {
"type": "text",
"fields": {
"ngram": {
"type": "text",
"analyzer": "pageIndexAnalyzer",
"search_analyzer": "standard"
}
}
}
}
}
}
}
2) Index some sample docs
POST my_index/pages/_bulk
{"index":{}}
{"name":"Harry Potter"}
{"index":{}}
{"name":"Hermione Granger"}
3) Run the a match query against the ngram field
POST my_index/pages/_search
{
"query": {
"match": {
"query": "Har",
"operator": "and"
}
}
}
I think it is better to use match_phrase_prefix query without using .keyword suffix. Check the docs at here https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-match-query-phrase-prefix.html
I have a problem with ElasticSearch language analyzer. I am working on Lithuanian language, so I am using Lithuanian language analyzer. Analyzer works fine and I got all word cases I need. For example, I index Lithuania city "Klaipėda":
PUT /cities/city/1
{
"name": "Klaipėda"
}
Problem is that I also need to get a result, when I am searching "Klaipėda" only in Latin alphabet ("Klaipeda") and in all Lithuanian cases:
Nomanitive case: "Klaipeda"
Genitive case: "Klaipedos"
...
Locative case: "Klaipedoje"
"Klaipėda", "Klaipėdos", "Klaipėdoje" - works, but "Klaipeda", "Klaipedos", "Klaipedoje" - not.
My index:
PUT /cities
{
"mappings": {
"city": {
"properties": {
"name": {
"type": "string",
"analyzer": "lithuanian",
"fields": {
"folded": {
"type": "string",
"analyzer": "md_folded_analyzer"
}
}
}
}
}
},
"settings": {
"analysis": {
"analyzer": {
"md_folded_analyzer": {
"type": "lithuanian",
"tokenizer": "standard",
"filter": [
"lowercase",
"asciifolding",
"lithuanian_stop",
"lithuanian_keywords",
"lithuanian_stemmer"
]
}
}
}
}
}
and search query:
GET /cities/_search
{
"query": {
"multi_match" : {
"type": "most_fields",
"query": "klaipeda",
"fields": [ "name", "name.folded" ]
}
}
}
What I am doing wrong? Thanks for help.
The technique you are using here is so-called multi-fields. The limitation of the underlying name.folded field is that you can't perform search against it - you can perform only sorting by name.folded and aggregation.
To make a way round this I've come up with the following set-up:
Separate fields set-up (to eliminate duplicates - just specify copy_to):
curl -XPUT http://localhost:9200/cities -d '
{
"mappings": {
"city": {
"properties": {
"name": {
"type": "string",
"analyzer": "lithuanian",
"copy_to": "folded",
},
"folded": {
"type": "string",
"analyzer": "md_folded_analyzer"
}
}
}
}
}'
Change the type of your analyzer to custom as it described here, because otherwise the asciifolding is not got into the config. And more important - asciifolding should go after all stemming / stop-words in Lithuanian language, because after folding the word can miss desired sense.
curl -XPUT http://localhost:9200/my_cities -d '
{
"settings": {
"analysis": {
"filter": {
"lithuanian_stop": {
"type": "stop",
"stopwords": "_lithuanian_"
},
"lithuanian_stemmer": {
"type": "stemmer",
"language": "lithuanian"
}
},
"analyzer": {
"md_folded_analyzer": {
"type": "custom",
"tokenizer": "standard",
"filter": [
"lowercase",
"lithuanian_stop",
"lithuanian_stemmer",
"asciifolding"
]
}
}
}
}
}
Sorry I've eliminated lithuanian_keywords - it requires additional set-up, which I missed here. But I hope you've got the idea.
I built an ElasticSearch index using a custom analyzer which uses letter tokenizer and lower_case and word_delimiter token filters. Then I tried searching for documents containing underscore-separated sub-words, e.g. abc_xyz, using only one of the sub-words, e.g. abc, but it didn't come back with any result. When I tried the full-word, i.e. abc_xyz, it did find the document.
Then I changed the document to have dash-separated sub-words instead, e.g. abc-xyz and tried to search by sub-words again and it worked.
To try to understand what is going on, I thought I would check the terms generated for my documents using _termvector service, and the result was identical for both, the underscore-separated sub-words and the dash-separated sub-words, so really I expect the result of searching to be identical in both cases.
Any idea what I could be doing wrong?
If it helps, this is the settings I used for my index:
{
"settings": {
"index": {
"analysis": {
"analyzer": {
"cmt_value_analyzer": {
"tokenizer": "letter",
"filter": [
"lowercase",
"my_filter"
],
"type": "custom"
}
},
"filter": {
"my_filter": {
"type": "word_delimiter"
}
}
}
}
},
"mappings": {
"alertmodel": {
"properties": {
"name": {
"analyzer": "cmt_value_analyzer",
"term_vector": "with_positions_offsets_payloads",
"type": "string"
},
"productId": {
"type": "double"
},
"productName": {
"analyzer": "cmt_value_analyzer",
"term_vector": "with_positions_offsets_payloads",
"type": "string"
},
"link": {
"analyzer": "cmt_value_analyzer",
"term_vector": "with_positions_offsets_payloads",
"type": "string"
},
"updatedOn": {
"type": "date"
}
}
}
}
}
I'm starting to learn Elasticsearch and now I am trying to write my first analyser configuration. What I want to achieve is that substrings are found if they are at the beginning or ending of a word. If I have the word "stackoverflow" and I search for "stack" I want to find it and when I search for "flow" I want to find it, but I do not want to find it when searching for "ackov" (in my use case this would not make sense).
I know there is the "Edge n gram tokenizer", but one analyser can only have one tokenizer and the edge n-gram can either be front or back (but not both at the same time).
And if I understood correctly, applying both version of the "Edge ngram filter" (front and back) to the analyzer, then I would not find either, because both filters need to return true, isn't it? Because "stack" wouldn't be in the ending of the word, so the back edge n gram filter would return false and the word "stackoverflow" would not be found.
So, how do I configure my analyzer to find substrings either in the end or in the beginning of a word, but not in the middle?
What can be done is to define two analyzers, one for matching at the start of a string and another to match at the end of a string. In the index settings below, I named the former one prefix_edge_ngram_analyzer and the latter one suffix_edge_ngram_analyzer. Those two analyzers can be applied to a multi-field string field to the text.prefix sub-field, respectively to the text.suffix string field.
{
"settings": {
"analysis": {
"analyzer": {
"prefix_edge_ngram_analyzer": {
"tokenizer": "prefix_edge_ngram_tokenizer",
"filter": ["lowercase"]
},
"suffix_edge_ngram_analyzer": {
"tokenizer": "keyword",
"filter" : ["lowercase","reverse","suffix_edge_ngram_filter","reverse"]
}
},
"tokenizer": {
"prefix_edge_ngram_tokenizer": {
"type": "edgeNGram",
"min_gram": "2",
"max_gram": "25"
}
},
"filter": {
"suffix_edge_ngram_filter": {
"type": "edgeNGram",
"min_gram": 2,
"max_gram": 25
}
}
}
},
"mappings": {
"test_type": {
"properties": {
"text": {
"type": "string",
"fields": {
"prefix": {
"type": "string",
"analyzer": "prefix_edge_ngram_analyzer"
},
"suffix": {
"type": "string",
"analyzer": "suffix_edge_ngram_analyzer"
}
}
}
}
}
}
}
Then let's say we index the following test document:
PUT test_index/test_type/1
{ "text": "stackoverflow" }
We can then search either by prefix or suffix using the following queries:
# input is "stack" => 1 result
GET test_index/test_type/_search?q=text.prefix:stack OR text.suffix:stack
# input is "flow" => 1 result
GET test_index/test_type/_search?q=text.prefix:flow OR text.suffix:flow
# input is "ackov" => 0 result
GET test_index/test_type/_search?q=text.prefix:ackov OR text.suffix:ackov
Another way to query with the query DSL:
POST test_index/test_type/_search
{
"query": {
"multi_match": {
"query": "stack",
"fields": [ "text.*" ]
}
}
}
UPDATE
If you already have a string field, you can "upgrade" it to a multi-field and create the two required sub-fields with their analyzers. The way to do this would be to do this in order:
Close your index in order to create the analyzers
POST test_index/_close
Update the index settings
PUT test_index/_settings
{
"analysis": {
"analyzer": {
"prefix_edge_ngram_analyzer": {
"tokenizer": "prefix_edge_ngram_tokenizer",
"filter": ["lowercase"]
},
"suffix_edge_ngram_analyzer": {
"tokenizer": "keyword",
"filter" : ["lowercase","reverse","suffix_edge_ngram_filter","reverse"]
}
},
"tokenizer": {
"prefix_edge_ngram_tokenizer": {
"type": "edgeNGram",
"min_gram": "2",
"max_gram": "25"
}
},
"filter": {
"suffix_edge_ngram_filter": {
"type": "edgeNGram",
"min_gram": 2,
"max_gram": 25
}
}
}
}
Re-open your index
POST test_index/_open
Finally, update the mapping of your text field
PUT test_index/_mapping/test_type
{
"properties": {
"text": {
"type": "string",
"fields": {
"prefix": {
"type": "string",
"analyzer": "prefix_edge_ngram_analyzer"
},
"suffix": {
"type": "string",
"analyzer": "suffix_edge_ngram_analyzer"
}
}
}
}
}
You still need to re-index all your documents in order for the new sub-fields text.prefix and text.suffix to be populated and analyzed.