Highlighting matched text in Elasticsearch - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the field to highlight in an Elasticsearch query.

Elasticsearch

{
  "query": {
    "match": {
      "content": "search text"
    }
  },
  "highlight": {
    "fields": {
      "[1]": {}
    }
  }
}

Drag options to blanks, or click blank then click option'

Acontent

Btitle

Cauthor

Ddate

Attempts:

3 left

💡 Hint

Common Mistakes

Using a field name different from the one in the query.

Forgetting to specify the field inside the highlight fields.

The highlight section must specify the field name where matches are highlighted. Here, the field is content.

2fill in blank

medium

Complete the code to set the pre-tags for highlighted text in Elasticsearch.

Elasticsearch

{
  "highlight": {
    "pre_tags": ["[1]"],
    "post_tags": ["</em>"],
    "fields": {
      "content": {}
    }
  }
}

Drag options to blanks, or click blank then click option'

A<strong>

B<b>

C<mark>

D<em>

Attempts:

3 left

💡 Hint

Common Mistakes

Using tags that do not match the post-tags.

Using tags that are not valid HTML tags.

The pre_tags define the opening tag for highlighted text. Commonly, <em> is used to emphasize matched text.

3fill in blank

hard

Fix the error in the highlight section to correctly specify multiple fields to highlight.

Elasticsearch

{
  "highlight": {
    "fields": {
      "title": {},
      "[1]": {}
    }
  }
}

Drag options to blanks, or click blank then click option'

Acontent

Bhighlight

Cmatch

Dfields

Attempts:

3 left

💡 Hint

Common Mistakes

Using reserved keywords like fields or match as field names.

Using invalid field names that do not exist in the index.

To highlight multiple fields, list each field name under fields. Here, content is the second field to highlight.

4fill in blank

hard

Fill both blanks to highlight the field and set the fragment size in Elasticsearch.

Elasticsearch

{
  "highlight": {
    "fields": {
      "[1]": {
        "fragment_size": [2]
      }
    }
  }
}

Drag options to blanks, or click blank then click option'

Acontent

Btitle

C150

D50

Attempts:

3 left

💡 Hint

Common Mistakes

Setting fragment_size to a string instead of a number.

Using a field name that does not match the query.

The field to highlight is content. The fragment_size controls the size of the highlighted snippet, here set to 150 characters.

5fill in blank

hard

Fill all three blanks to highlight a field with custom tags and number of fragments.

Elasticsearch

{
  "highlight": {
    "pre_tags": ["[1]"],
    "post_tags": ["[2]"],
    "fields": {
      "content": {
        "number_of_fragments": [3]
      }
    }
  }
}

Drag options to blanks, or click blank then click option'

A<em>

B</em>

C3

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching pre and post tags.

Using a string instead of a number for number_of_fragments.

The pre_tags and post_tags define the HTML tags wrapping the highlighted text. The number_of_fragments controls how many highlighted snippets are returned, here 3.

Practice

1. What is the main purpose of the highlight section in an Elasticsearch query?

easy

A. To filter documents before searching

B. To sort the search results by relevance

C. To update documents in the index

D. To show matched words clearly in search results

Solution

1. Step 1: Understand the role of highlighting

   Highlighting is used to emphasize matched words in search results so users can see why a document matched.

2. Step 2: Compare with other query parts

   Sorting, filtering, and updating are different functions not related to highlighting matched text.

3. Final Answer:

   To show matched words clearly in search results -> Option D

4. Quick Check:

   Highlight = show matched words [OK]

Hint: Highlight section shows matched words in results [OK]

Common Mistakes:

• Confusing highlight with sorting or filtering
• Thinking highlight updates documents
• Assuming highlight changes search relevance

2. Which of the following is the correct syntax to add highlighting for the field content in an Elasticsearch query?

easy

A. "highlight": {"fields": {"content": {}}}

B. "highlight": {"field": "content"}

C. "highlight": {"content": {"fields": {}}}

D. "highlight": {"fields": ["content"]}

Solution

1. Step 1: Recall correct highlight syntax

   The correct syntax uses "highlight" with "fields" as an object mapping field names to options, like {"content": {}}.

2. Step 2: Check each option

   "highlight": {"fields": {"content": {}}} matches the correct structure. Options B, C, and D use incorrect keys or data types.

3. Final Answer:

   "highlight": {"fields": {"content": {}}} -> Option A

4. Quick Check:

   Highlight fields syntax = "highlight": {"fields": {"content": {}}} [OK]

Hint: Use "highlight": {"fields": {"fieldname": {}}} [OK]

Common Mistakes:

• Using "field" instead of "fields"
• Putting fields inside an array instead of object
• Misplacing keys inside highlight

3. Given this Elasticsearch query snippet, what will the highlight section return for a match in the title field?

{
  "query": {"match": {"title": "quick fox"}},
  "highlight": {"fields": {"title": {}}}
}

medium

A. An error because highlight requires custom tags

B. Only the word "quick" highlighted, "fox" ignored

C. The matched words "quick" and "fox" wrapped in default highlight tags

D. No highlighting because tags are missing

Solution

1. Step 1: Understand default highlight behavior

   When highlight is enabled with empty options, Elasticsearch wraps matched words with default tags like <em> and </em>.

2. Step 2: Analyze the query

   The query matches both "quick" and "fox" in the title, so both words will be highlighted.

3. Final Answer:

   The matched words "quick" and "fox" wrapped in default highlight tags -> Option C

4. Quick Check:

   Default highlight tags wrap matched words [OK]

Hint: Empty highlight options use default tags to wrap matches [OK]

Common Mistakes:

• Thinking highlight needs custom tags to work
• Assuming only first matched word is highlighted
• Believing missing tags cause errors

4. Identify the error in this Elasticsearch highlight query snippet:

{
  "query": {"match": {"description": "fast car"}},
  "highlight": {"fields": ["description"]}
}

medium

A. "match" query is invalid for highlighting

B. "fields" should be an object, not an array

C. "highlight" must be inside "query"

D. "description" field cannot be highlighted

Solution

1. Step 1: Check highlight fields syntax

   The "fields" key must be an object mapping field names to options, not an array.

2. Step 2: Verify other parts

   "match" query is valid, "highlight" is correctly placed, and any field can be highlighted if indexed.

3. Final Answer:

   "fields" should be an object, not an array -> Option B

4. Quick Check:

   Highlight fields = object, not array [OK]

Hint: Highlight fields must be an object, not a list [OK]

Common Mistakes:

• Using array instead of object for fields
• Placing highlight inside query incorrectly
• Assuming some fields can't be highlighted

5. You want to highlight matched text in both title and content fields with custom tags <strong> and </strong>. Which is the correct highlight section to achieve this?

hard

A. "highlight": {"fields": {"title": {}, "content": {}}, "pre_tags": [""], "post_tags": [""]}

B. "highlight": {"fields": ["title", "content"], "pre_tags": "", "post_tags": ""}

C. "highlight": {"fields": {"title": {"tags": ["", ""]}, "content": {"tags": ["", ""]}}}

D. "highlight": {"fields": {"title": {}, "content": {}}, "tags": ["", ""]}

Solution

1. Step 1: Understand how to set custom tags

   Custom tags are set globally using "pre_tags" and "post_tags" arrays outside the fields object.

2. Step 2: Check each option's structure

   "highlight": {"fields": {"title": {}, "content": {}}, "pre_tags": [""], "post_tags": [""]} correctly sets "fields" as an object and uses "pre_tags" and "post_tags" arrays. Options B, C, and D misuse keys or data types.

3. Final Answer:

   "highlight": {"fields": {"title": {}, "content": {}}, "pre_tags": [""], "post_tags": [""]} -> Option A

4. Quick Check:

   Custom tags use pre_tags/post_tags arrays [OK]

Hint: Use pre_tags/post_tags arrays for custom highlight tags [OK]

Common Mistakes:

• Using arrays for fields instead of objects
• Setting tags inside each field incorrectly
• Using single strings instead of arrays for tags