Partial updates in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this partial update script?

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

Elasticsearch

{
  "script": {
    "source": "ctx._source.counter += params.increment",
    "params": {"increment": 3}
  }
}

A The <code>counter</code> field will be set to 3 regardless of its previous value.

B The <code>counter</code> field will increase by 3 from its current value.

C The update will fail because <code>ctx._source.counter</code> is not defined.

D The <code>counter</code> field will be removed from the document.

💡 Hint

Think about how the script modifies the existing field value.

The script uses ctx._source.counter += params.increment which adds 3 to the existing counter value. It does not overwrite or remove it.

❓ Predict Output

intermediate

What happens if you use a partial update with a nested field?

Consider this partial update request to change a nested field address.city. What will be the result?

Elasticsearch

{
  "doc": {
    "address": {
      "city": "Newville"
    }
  }
}

A Only the <code>city</code> inside <code>address</code> is updated; other <code>address</code> fields remain unchanged.

B The entire <code>address</code> object is replaced with {"city": "Newville"}.

C The update will fail because nested fields cannot be updated partially.

D The <code>city</code> field is added at the root level, not inside <code>address</code>.

💡 Hint

Partial updates merge the provided fields into the existing document.

Partial updates merge the provided nested fields into the existing object, so only city changes while other address fields stay the same.

🔧 Debug

advanced

Why does this partial update script cause an error?

This update script is intended to add a tag to a list field tags. 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 script syntax is invalid because it lacks a return statement.

C The parameter <code>new_tag</code> is not passed correctly.

D The <code>tags</code> field is null or missing, so calling <code>add</code> causes a NullPointerException.

💡 Hint

Check if the tags field exists and is initialized as a list.

If tags is missing or null, calling add on it causes an error. You must ensure tags is a list before adding.

🧠 Conceptual

advanced

What is the effect of using doc_as_upsert in a partial update?

When you set doc_as_upsert to true in an update request, what happens if the document does not exist?

A The partial document is inserted as a new document.

B The update fails with a document not found error.

C The update request is ignored silently.

D A new empty document is created without the partial fields.

💡 Hint

Think about how upsert works in Elasticsearch.

Setting doc_as_upsert to true means if the document does not exist, Elasticsearch inserts the partial document as a new one.

❓ Predict Output

expert

What is the final document after this partial update with a script?

Given the document {"count": 5, "tags": ["old"]} and this update request, what is the final document?

Elasticsearch

{
  "script": {
    "source": "ctx._source.count = params.count; ctx._source.tags.add(params.tag)",
    "params": {"count": 10, "tag": "new"}
  }
}

A {"count": 5, "tags": ["old", "new"]}

B {"count": 10, "tags": ["new"]}

C {"count": 10, "tags": ["old", "new"]}

D The update fails with a NullPointerException.

💡 Hint

The script sets count and adds a tag to the existing list.

The script sets count to 10 and adds "new" to the existing tags list, resulting in {"count": 10, "tags": ["old", "new"]}.