Runtime fields in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a runtime script field calculation

What is the output of the following runtime field script when applied to a document with price = 100 and tax = 0.15?

Elasticsearch

{
  "runtime_mappings": {
    "total_price": {
      "type": "double",
      "script": {
        "source": "emit(doc['price'].value * (1 + doc['tax'].value))"
      }
    }
  }
}

A Error: field not found

B 15.0

C 100.15

D 115.0

💡 Hint

Remember the formula for total price including tax is price * (1 + tax).

The script multiplies the price (100) by 1 plus the tax rate (0.15), resulting in 100 * 1.15 = 115.0.

❓ Predict Output

intermediate

Runtime field with conditional logic output

Given the runtime field script below, what value will it emit for a document with status = "active"?

Elasticsearch

{
  "runtime_mappings": {
    "status_flag": {
      "type": "keyword",
      "script": {
        "source": "if (doc['status'].value == 'active') { emit('1') } else { emit('0') }"
      }
    }
  }
}

A "1"

B "0"

C "active"

D null

💡 Hint

Check the condition comparing the status field value.

The script checks if the status is 'active' and emits '1' if true, otherwise '0'. Since status is 'active', it emits '1'.

❓ Predict Output

advanced

Output of runtime field script with array field

What will the runtime field script emit for a document where scores = [10, 20, 30]?

Elasticsearch

{
  "runtime_mappings": {
    "max_score": {
      "type": "long",
      "script": {
        "source": "emit(Collections.max(doc['scores'].values))"
      }
    }
  }
}

A 20

B 10

C 30

D Error: Collections not defined

💡 Hint

The script uses Collections.max to find the highest value in the scores array.

The script finds the maximum value in the scores array [10, 20, 30], which is 30.

❓ Predict Output

advanced

Runtime field script error type

What error will occur when running this runtime field script if the document does NOT have the discount field?

Elasticsearch

{
  "runtime_mappings": {
    "final_price": {
      "type": "double",
      "script": {
        "source": "emit(doc['price'].value * (1 - doc['discount'].value))"
      }
    }
  }
}

A IndexOutOfBoundsException

B NullPointerException

C NoSuchFieldException

D ArithmeticException

💡 Hint

Accessing a missing field's value causes a null reference error.

If the discount field is missing, accessing doc['discount'].value causes a NullPointerException in the script.

🧠 Conceptual

expert

Number of runtime fields created by this mapping

Given the following runtime_mappings configuration, how many runtime fields will be created?

Elasticsearch

{
  "runtime_mappings": {
    "field1": { "type": "keyword", "script": { "source": "emit('a')" } },
    "field2": { "type": "long", "script": { "source": "emit(1)" } },
    "field3": { "type": "double", "script": { "source": "emit(1.0)" } },
    "field4": { "type": "boolean", "script": { "source": "emit(true)" } },
    "field5": { "type": "date", "script": { "source": "emit(params._source['date_field'])" } }
  }
}

A 5

B 4

C 3

D 0

💡 Hint

Count each runtime field defined under runtime_mappings.

There are 5 runtime fields defined: field1, field2, field3, field4, and field5.