Updating documents in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Elasticsearch update script?

Given the following update request, what will be the value of the field counter after the update?

Elasticsearch

{
  "script" : {
    "source" : "ctx._source.counter += params.count",
    "params" : {
      "count" : 4
    }
  }
}

A The <code>counter</code> field will be set to 4

B The <code>counter</code> field will increase by 4

C The <code>counter</code> field will decrease by 4

D The update will fail with a script error

💡 Hint

Look at the script source and the operation it performs on ctx._source.counter.

The script uses ctx._source.counter += params.count which means it adds the value of params.count (4) to the existing counter field. So the field increases by 4.

❓ Predict Output

intermediate

What happens if you try to update a non-existent document?

Consider this update request targeting a document ID that does not exist. What is the expected result?

Elasticsearch

{
  "doc" : {
    "status" : "active"
  }
}

A Elasticsearch returns a 404 error indicating document not found

B Elasticsearch creates a new document with the given fields

C Elasticsearch updates the document silently without error

D Elasticsearch throws a script error

💡 Hint

Think about the default behavior of update requests on missing documents.

By default, an update request on a non-existent document returns a 404 error. It does not create a new document unless doc_as_upsert is set to true.

🔧 Debug

advanced

Why does this update script fail with a runtime error?

This update script is intended to append a new tag to the tags array. Why does it fail?

Elasticsearch

{
  "script": {
    "source": "ctx._source.tags.add(params.new_tag)",
    "params": {
      "new_tag": "urgent"
    }
  }
}

A The <code>add</code> method is not supported in Elasticsearch scripts

B The parameter <code>new_tag</code> is not passed correctly

C The script syntax is invalid due to missing semicolon

D The <code>tags</code> field is null or missing, so <code>add</code> method fails

💡 Hint

Check if the tags field exists and is an array before calling add.

If tags is missing or null, calling add on it causes a runtime error because you cannot call methods on null.

📝 Syntax

advanced

Which update script syntax is correct to conditionally update a field?

You want to update the status field to "closed" only if its current value is "open". Which script is correct?

A "source": "if (ctx._source.status === 'open') { ctx._source.status = 'closed' }"

B "source": "if (ctx._source.status = 'open') { ctx._source.status = 'closed' }"

C "source": "if (ctx._source.status == 'open') { ctx._source.status = 'closed' }"

D "source": "if ctx._source.status == 'open' { ctx._source.status = 'closed' }"

💡 Hint

Check the syntax for if statements and equality operators in painless scripts.

Option C uses correct painless script syntax: parentheses around condition, double equals for comparison, and braces for the block.

🚀 Application

expert

How to atomically increment a nested field in an update request?

You have a document with a nested field metrics.views. Which update request correctly increments views by 1 atomically?

A { "script": { "source": "ctx._source.metrics.views += 1" } }

B { "doc": { "metrics.views": "metrics.views + 1" } }

C { "script": { "source": "ctx._source['metrics.views'] += 1" } }

D { "doc": { "metrics": { "views": "metrics.views + 1" } } }

💡 Hint

Think about how to access nested fields in painless scripts and how to increment them.

Option A correctly uses painless script syntax to increment the nested field metrics.views. Options B and D try to update with strings, which is invalid. Option A uses incorrect syntax for nested field access.