Search-as-you-type field in Elasticsearch

Introduction

A search-as-you-type field helps users find what they want quickly by showing results while they type. It makes searching faster and easier.

When building a website search box that shows suggestions as you type.

When creating a product catalog where users can find items quickly.

When making a contact list that filters names instantly.

When you want to improve user experience by reducing typing effort.

When you want to handle partial words or prefixes in search queries.

Syntax

Elasticsearch

PUT /my_index
{
  "mappings": {
    "properties": {
      "my_field": {
        "type": "search_as_you_type"
      }
    }
  }
}

The search_as_you_type field type creates special subfields to support fast prefix matching.

You use this field type in your index mapping before adding documents.

Examples

This creates a name field that supports search-as-you-type for product names.

Elasticsearch

PUT /products
{
  "mappings": {
    "properties": {
      "name": {
        "type": "search_as_you_type"
      }
    }
  }
}

This query searches for terms starting with "iph" in the name field and its subfields.

Elasticsearch

GET /products/_search
{
  "query": {
    "multi_match": {
      "query": "iph",
      "type": "bool_prefix",
      "fields": [
        "name",
        "name._2gram",
        "name._3gram"
      ]
    }
  }
}

Sample Program

This example creates an index called library with a title field that supports search-as-you-type. It adds two books and then searches for titles starting with "Grea".

Elasticsearch

PUT /library
{
  "mappings": {
    "properties": {
      "title": {
        "type": "search_as_you_type"
      }
    }
  }
}

POST /library/_doc/1
{
  "title": "The Great Gatsby"
}

POST /library/_doc/2
{
  "title": "Great Expectations"
}

GET /library/_search
{
  "query": {
    "multi_match": {
      "query": "Grea",
      "type": "bool_prefix",
      "fields": [
        "title",
        "title._2gram",
        "title._3gram"
      ]
    }
  }
}

Important Notes

Search-as-you-type fields create hidden subfields with n-grams to speed up prefix searches.

Use multi_match with bool_prefix type to query these fields effectively.

Remember to reindex your data after changing mappings.

Summary

Search-as-you-type fields help users find matches while typing.

Define the field with type: search_as_you_type in your mapping.

Use multi_match queries with bool_prefix to search these fields.

Practice

1. What is the main purpose of a search_as_you_type field in Elasticsearch?

easy

A. To provide instant search results as the user types each character

B. To store large binary files efficiently

C. To perform complex aggregations on numeric data

D. To index documents only after full text is entered

Solution

1. Step 1: Understand the purpose of search_as_you_type

   The search_as_you_type field is designed to help users get search results instantly as they type, improving user experience.

2. Step 2: Compare with other options

   Options B, C, and D describe unrelated Elasticsearch features like binary storage, aggregations, or delayed indexing, which are not related to search_as_you_type.

3. Final Answer:

   To provide instant search results as the user types each character -> Option A

4. Quick Check:

   search_as_you_type = instant search while typing [OK]

Hint: Remember: search_as_you_type means live search suggestions [OK]

Common Mistakes:

• Confusing search_as_you_type with binary or numeric fields
• Thinking it delays indexing until full input
• Assuming it is for aggregations

2. Which is the correct way to define a search_as_you_type field in an Elasticsearch mapping?

easy

A. "title": { "type": "text" }

B. "title": { "type": "completion" }

C. "title": { "type": "keyword" }

D. "title": { "type": "search_as_you_type" }

Solution

1. Step 1: Identify the correct field type for search-as-you-type

   The search_as_you_type field type must be explicitly set as "type": "search_as_you_type" in the mapping.

2. Step 2: Eliminate other field types

   "title": { "type": "text" } uses text, which is for full text search but not optimized for search-as-you-type. "title": { "type": "keyword" } uses keyword, which is for exact matches. "title": { "type": "completion" } uses completion, which is for autocomplete but different from search_as_you_type.

3. Final Answer:

   "title": { "type": "search_as_you_type" } -> Option D

4. Quick Check:

   Mapping type for search-as-you-type = search_as_you_type [OK]

Hint: Use type "search_as_you_type" exactly in mapping [OK]

Common Mistakes:

• Using "text" instead of "search_as_you_type"
• Confusing with "completion" type
• Omitting the type field

3. Given this mapping snippet:

{
  "mappings": {
    "properties": {
      "name": { "type": "search_as_you_type" }
    }
  }
}

Which query will correctly search for documents where the name field starts with "mic"?

medium

A. { "match": { "name": "mic" } }

B. { "multi_match": { "query": "mic", "type": "bool_prefix", "fields": ["name", "name._2gram", "name._3gram"] } }

C. { "term": { "name": "mic" } }

D. { "prefix": { "name": "mic" } }

Solution

1. Step 1: Understand how to query search_as_you_type fields

   Search-as-you-type fields require a multi_match query with type: bool_prefix and fields including the base field and its n-gram subfields.

2. Step 2: Analyze each query option

   { "match": { "name": "mic" } } uses simple match, which does not support prefix matching well. { "term": { "name": "mic" } } uses term query, which requires exact match. { "prefix": { "name": "mic" } } uses prefix query, which is not optimized for search_as_you_type. { "multi_match": { "query": "mic", "type": "bool_prefix", "fields": ["name", "name._2gram", "name._3gram"] } } correctly uses multi_match with bool_prefix and the required fields.

3. Final Answer:

   { "multi_match": { "query": "mic", "type": "bool_prefix", "fields": ["name", "name._2gram", "name._3gram"] } } -> Option B

4. Quick Check:

   Use multi_match + bool_prefix + ngram fields [OK]

Hint: Use multi_match with bool_prefix and ngram fields [OK]

Common Mistakes:

• Using term or prefix queries alone
• Not including ngram subfields in fields list
• Using simple match query for prefix search

4. You wrote this query to search a search_as_you_type field but get no results:

{ "multi_match": { "query": "app", "type": "bool_prefix", "fields": ["title"] } }

What is the likely problem?

medium

A. The field 'title' must be of type 'keyword' for this query

B. The 'bool_prefix' type is invalid for multi_match queries

C. The query should include ngram subfields like 'title._2gram' and 'title._3gram'

D. The query string 'app' is too short to match anything

Solution

1. Step 1: Check query fields for search_as_you_type

   Search-as-you-type fields generate subfields with ngrams like '_2gram' and '_3gram' that must be included in the query fields for prefix matching.

2. Step 2: Identify missing ngram subfields in the query

   The query only searches 'title' field, missing 'title._2gram' and 'title._3gram', so it won't match prefixes properly.

3. Final Answer:

   The query should include ngram subfields like 'title._2gram' and 'title._3gram' -> Option C

4. Quick Check:

   Include ngram subfields in fields list for prefix search [OK]

Hint: Always add _2gram and _3gram subfields in multi_match fields [OK]

Common Mistakes:

• Omitting ngram subfields in fields list
• Thinking bool_prefix is invalid
• Assuming keyword type is needed
• Blaming query length

5. You want to implement a search-as-you-type feature for a product catalog with a name field. Which of the following mapping and query combinations will correctly support prefix matching as the user types?

hard

A. Mapping: { "name": { "type": "search_as_you_type" } }Query: { "multi_match": { "query": "lap", "type": "bool_prefix", "fields": ["name", "name._2gram", "name._3gram"] } }

B. Mapping: { "name": { "type": "text" } }Query: { "match": { "name": "lap" } }

C. Mapping: { "name": { "type": "keyword" } }Query: { "prefix": { "name": "lap" } }

D. Mapping: { "name": { "type": "completion" } }Query: { "term": { "name": "lap" } }

Solution

1. Step 1: Choose the correct mapping for search-as-you-type

   The search_as_you_type type is designed for prefix matching and instant search as the user types.

2. Step 2: Use the correct query for prefix matching

   The multi_match query with bool_prefix type and fields including the base field and its ngram subfields is required for effective prefix matching.

3. Step 3: Evaluate other options

   Mapping: { "name": { "type": "text" } }
   Query: { "match": { "name": "lap" } } uses text with simple match, which does not support prefix search well. Mapping: { "name": { "type": "keyword" } }
   Query: { "prefix": { "name": "lap" } } uses keyword with prefix query, which is less flexible. Mapping: { "name": { "type": "completion" } }
   Query: { "term": { "name": "lap" } } uses completion with term query, which is incorrect usage.

4. Final Answer:

   Mapping: { "name": { "type": "search_as_you_type" } } and Query: { "multi_match": { "query": "lap", "type": "bool_prefix", "fields": ["name", "name._2gram", "name._3gram"] } } -> Option A

5. Quick Check:

   search_as_you_type + multi_match bool_prefix + ngram fields = correct [OK]

Hint: Combine search_as_you_type mapping with multi_match bool_prefix query [OK]

Common Mistakes:

• Using text type with match query for prefix search
• Using keyword type with prefix query only
• Confusing completion type with search_as_you_type
• Using term query for prefix matching