Nested queries for nested objects in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a nested query filtering by nested field

Given the following Elasticsearch nested query, what is the expected output when searching an index with documents containing nested 'comments' objects?

{
  "query": {
    "nested": {
      "path": "comments",
      "query": {
        "bool": {
          "must": [
            { "match": { "comments.author": "alice" } },
            { "range": { "comments.likes": { "gte": 10 } } }
          ]
        }
      }
    }
  }
}

Assuming the index has documents with nested comments by various authors with different likes, which option best describes the result?

A Documents that have comments with author 'alice' and comments with likes >= 10, but not necessarily in the same comment.

B Documents that have at least one comment by 'alice' with 10 or more likes.

C Documents that have all comments by 'alice' with 10 or more likes.

D Documents that have any comment by 'alice' or any comment with 10 or more likes.

💡 Hint

Remember that nested queries match nested objects individually, not across different nested objects.

The nested query filters documents where at least one nested 'comments' object matches both conditions: author is 'alice' and likes are 10 or more. It does not combine conditions across different nested objects.

🧠 Conceptual

intermediate

Understanding the purpose of nested queries

Why do we use nested queries in Elasticsearch when dealing with nested objects instead of regular queries?

A Because nested queries allow matching conditions on the same nested object, preserving object relationships.

B Because nested queries improve performance by indexing nested objects separately.

C Because nested queries automatically flatten nested objects into the root document.

D Because nested queries are required to search any field in Elasticsearch.

💡 Hint

Think about how nested objects are stored and how queries match them.

Nested queries ensure that conditions apply to the same nested object instance, preserving the relationship between fields inside that object. Regular queries might match fields from different nested objects incorrectly.

🔧 Debug

advanced

Identify the error in this nested query

What error will this Elasticsearch query produce?

{
  "query": {
    "nested": {
      "path": "comments",
      "query": {
        "match": {
          "author": "bob"
        }
      }
    }
  }
}

Assuming 'comments' is a nested field, what is wrong?

A It will cause a type mismatch error because 'author' is not a string field.

B It will run correctly and return documents with comments by 'bob'.

C It will cause a syntax error due to missing closing braces.

D It will cause a 'field [author] not found' error because the field path is incomplete inside nested query.

💡 Hint

Check the field name used inside the nested query's match clause.

Inside a nested query, the field names must be fully qualified with the nested path prefix. Using just 'author' instead of 'comments.author' causes Elasticsearch to not find the field.

📝 Syntax

advanced

Correct syntax for nested query with inner hits

Which of the following nested queries correctly includes inner hits to return matching nested objects?

A { "nested": { "path": "comments", "query": { "match": { "comments.text": "great" } }, "inner_hits": {} } }

B { "nested": { "path": "comments", "inner_hits": {}, "query": { "match": { "comments.text": "great" } } } }

C { "nested": { "query": { "match": { "comments.text": "great" } }, "path": "comments" } }

D { "nested": { "path": "comments", "query": { "match": { "text": "great" } }, "inner_hits": {} } }

💡 Hint

Check the order and presence of required keys and correct field names.

Option A correctly places 'path', 'query', and 'inner_hits' keys and uses the fully qualified field 'comments.text'. Option A has keys in wrong order (though order is not critical, but inner_hits should be after query), C misses inner_hits, D uses unqualified field 'text'.

🚀 Application

expert

Construct a nested query to find documents with nested comments by 'eve' having likes between 5 and 15

You want to find documents where at least one nested comment has author 'eve' and likes between 5 and 15 inclusive. Which query correctly implements this?

A { "query": { "nested": { "path": "comments", "query": { "match": { "comments.author": "eve" } }, "filter": { "range": { "comments.likes": { "gte": 5, "lte": 15 } } } } } }

B { "query": { "bool": { "must": [ { "match": { "comments.author": "eve" } }, { "range": { "comments.likes": { "gte": 5, "lte": 15 } } } ] } } }

C { "query": { "nested": { "path": "comments", "query": { "bool": { "must": [ { "match": { "comments.author": "eve" } }, { "range": { "comments.likes": { "gte": 5, "lte": 15 } } } ] } } } } }

D { "query": { "nested": { "path": "comments", "query": { "bool": { "should": [ { "match": { "comments.author": "eve" } }, { "range": { "comments.likes": { "gte": 5, "lte": 15 } } } ] } } } } }

💡 Hint

Use a bool must inside nested query to combine conditions on the same nested object.

Option C correctly uses a nested query with a bool must combining match and range conditions on the same nested object. Option C is not nested, so conditions may match different nested objects. Option C uses an invalid 'filter' key inside nested query. Option C uses 'should' which means either condition can match, not both.