Shantanu's Blog

Corporate Consultant

June 25, 2016

 

save lowercase data into elasticsearch

Most of the searches we do are case insensitive. Elasticsearch by default indexes data in lowercase. But there are times when we do not want to use any analyzer and still want to save the data in lowercase. The best option is to take care of not inserting data in capital letters. Here is an example.

# delete the index if exists
DELETE /test_index

# insert the records, table structure will be created automatically
POST /test_index/doc/_bulk
{"index":{"_id":1}}
{"cities":["new york","delhi"]}
{"index":{"_id":2}}
{"cities":["new york","Delhi","new Jersey"]}

# query to show how each word is indexed
POST /test_index/_search?search_type=count
{
   "aggs": {
      "city_terms": {
         "terms": {
            "field": "cities"
         }
      }
   }
}

This will return
delhi 2
new 2
york 2
jersey 1
_____

All the text is split on whitespace and lowercased to be saved with each document identifier. But we need "new york" 2 and "new jersey" 1. The single word "new" does not mean anything in this case. Elasticsearch will build the table structure dynamically for you. It has decided that the "cities" column should be of "string" type.

get /test_index/_mapping

{
   "test_index": {
      "mappings": {
         "doc": {
            "properties": {
               "cities": {
                  "type": "string"
               }
            }
         }
      }
   }
}

If we decide not to analyze the cities, then each value in the list will be saved together.

# delete index
DELETE /test_index

PUT /test_index
{
   "mappings": {
      "doc": {
         "properties": {
            "cities": {
               "type": "string",
               "index": "not_analyzed"
            }
         }
      }
   }
}

If you run the same insert and select queries again, then you will get
new york 2
Delhi 1
delhi 1
new Jersey 1

As you must have noticed we got separate entry for "Delhi" and "delhi" because of capitalization. To avoid this use all lowercase letters while inserting the data, or use the following query....

POST /test_index/_search?search_type=count
{
    "aggs": {
        "city_terms": {
            "terms": {
                "script": "doc.cities.values.collect{it.toLowerCase()}"
            }
}}}

You should now get the correct results:
delhi 2
new york 2
new jersey 1

Lowercase all the fields before inserting them into elasic.
1) If you are using Elasticsearch version 5.0 then you can use "Lowercase Processor" to convert certain fields to lowercase while inserting the records into database. I guess this is an important reason to upgrade. We can not rely on the data that we receive and processing the data to lowercase using python will be difficult.
2) If you are using logstash, then use mutate filter...

filter {
  mutate {
    lowercase => [ "fieldname" ]
  }
}

3) Use "lower" function of python or any other scripting language.

You can use any of the 3 methods mentioned above, but saving the data into lowercase fields will save a lot of confusion later.

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