Deleting documents in Elasticsearch - Mini Project: Build & Apply

Deleting documents

📖 Scenario: You manage a small online store's product catalog stored in Elasticsearch. Sometimes, products are discontinued and need to be removed from the catalog.

🎯 Goal: You will learn how to delete documents from an Elasticsearch index using the document ID and a query.

📋 What You'll Learn

Create an index with sample product documents

Set a variable for the product ID to delete

Write the command to delete a document by ID

Write the command to delete documents by a query

Print the deletion responses

💡 Why This Matters

🌍 Real World

Deleting outdated or discontinued products from an online store's Elasticsearch catalog keeps the data clean and relevant.

💼 Career

Knowing how to delete documents by ID or query is essential for managing data lifecycle in Elasticsearch, a common skill for backend developers and data engineers.

1

Create the product index with sample documents

Create an index called products with three documents having these exact IDs and fields:
1: {"name": "Laptop", "price": 1200},
2: {"name": "Smartphone", "price": 800},
3: {"name": "Tablet", "price": 400}.
Use the Elasticsearch index API calls as shown.

Elasticsearch

# Use the Elasticsearch index API to add documents
# Your code here

Hint

Use the POST /products/_doc/{id} endpoint to add each product document.

2

Set the product ID to delete

Create a variable called product_id and set it to the string "2" to represent the product to delete.

Elasticsearch

POST /products/_doc/1
{
  "name": "Laptop",
  "price": 1200
}

POST /products/_doc/2
{
  "name": "Smartphone",
  "price": 800
}

POST /products/_doc/3
{
  "name": "Tablet",
  "price": 400
}

# Create a variable called product_id and set it to "2"
# Your code here

Hint

In your client or script, assign the string "2" to a variable named product_id.

3

Delete the product document by ID

Write the Elasticsearch DELETE API call to delete the document with ID stored in product_id from the products index.

Elasticsearch

POST /products/_doc/1
{
  "name": "Laptop",
  "price": 1200
}

POST /products/_doc/2
{
  "name": "Smartphone",
  "price": 800
}

POST /products/_doc/3
{
  "name": "Tablet",
  "price": 400
}

product_id = "2"

# Write the DELETE API call to remove the document with ID product_id
# Your code here

Hint

Use DELETE /products/_doc/{product_id} to delete the document by ID.

4

Delete products by query and print results

Write the Elasticsearch POST API call to delete all products with price less than 1000 using _delete_by_query on the products index.
Then print the response showing how many documents were deleted.

Elasticsearch

POST /products/_doc/1
{
  "name": "Laptop",
  "price": 1200
}

POST /products/_doc/2
{
  "name": "Smartphone",
  "price": 800
}

POST /products/_doc/3
{
  "name": "Tablet",
  "price": 400
}

product_id = "2"

DELETE /products/_doc/2

# Write the _delete_by_query API call to delete products with price < 1000
# Print the number of deleted documents
# Your code here

Hint

Use POST /products/_delete_by_query with a range query on price less than 1000.

Practice

1.

Which Elasticsearch API method is used to delete a single document by its ID?

easy

A. GET method with document ID

B. DELETE method with document ID

C. POST method with document ID

D. PUT method with document ID

Solution

1. Step 1: Understand document deletion in Elasticsearch

   Deleting a single document requires specifying its ID and using the DELETE HTTP method.

2. Step 2: Identify the correct API method

   The DELETE method with the document ID is the standard way to remove one document.

3. Final Answer:

   DELETE method with document ID -> Option B

4. Quick Check:

   Delete single document = DELETE with ID [OK]

Hint: Use DELETE with document ID to remove one document fast [OK]

Common Mistakes:

• Using GET or POST instead of DELETE
• Trying to delete without specifying document ID
• Confusing _delete_by_query with single document deletion

2.

Which of the following is the correct syntax to delete a document with ID 123 from index products using Elasticsearch REST API?

?

easy

A. GET /products/_delete/123

B. POST /products/_doc/123/_delete

C. DELETE /products/_doc/123

D. PUT /products/_doc/123

Solution

1. Step 1: Recall the REST API syntax for deleting a document

   The correct syntax uses DELETE method on the path /index/_doc/document_id.

2. Step 2: Match the syntax with the options

   DELETE /products/_doc/123 matches DELETE /products/_doc/123 which is correct.

3. Final Answer:

   DELETE /products/_doc/123 -> Option C

4. Quick Check:

   Delete syntax = DELETE /index/_doc/id [OK]

Hint: DELETE + /index/_doc/document_id is the right syntax [OK]

Common Mistakes:

• Using POST or GET instead of DELETE
• Wrong URL path like _delete or missing _doc
• Using PUT which is for creating/updating

3.

Given this Elasticsearch _delete_by_query request to delete documents where status is "inactive":

{
  "query": {
    "term": { "status": "inactive" }
  }
}

What will be the result if there are 3 documents matching this query?

medium

A. Deletes 3 documents and returns success count 3

B. Deletes 0 documents because term query is incorrect

C. Deletes all documents in the index

D. Returns an error due to missing document ID

Solution

1. Step 1: Understand _delete_by_query behavior

   It deletes all documents matching the query, here documents with status "inactive".

2. Step 2: Apply to given query and data

   Since 3 documents match, all 3 will be deleted and success count will be 3.

3. Final Answer:

   Deletes 3 documents and returns success count 3 -> Option A

4. Quick Check:

   _delete_by_query deletes matching docs = 3 [OK]

Hint: Delete by query removes all matching docs, not just one [OK]

Common Mistakes:

• Thinking _delete_by_query needs document ID
• Assuming it deletes all documents regardless of query
• Confusing term query syntax

4.

What is wrong with this Elasticsearch delete request?

DELETE /users/_doc

It aims to delete a document but fails. Why?

medium

A. Missing document ID in the URL

B. Using DELETE instead of POST

C. Index name is incorrect

D. Missing request body with query

Solution

1. Step 1: Check the delete request URL format

   Deleting a document requires the document ID after _doc in the URL.

2. Step 2: Identify the missing part

   The request lacks the document ID, so Elasticsearch cannot identify which document to delete.

3. Final Answer:

   Missing document ID in the URL -> Option A

4. Quick Check:

   Delete URL needs document ID [OK]

Hint: Always include document ID after _doc in DELETE URL [OK]

Common Mistakes:

• Omitting document ID in delete URL
• Confusing DELETE with POST for deletion
• Thinking request body is needed for single delete

5.

You want to delete all documents from the orders index where the amount field is less than 100. Which Elasticsearch request correctly achieves this?

hard

A. DELETE /orders/_delete_by_query { "query": { "term": { "amount": 100 } } }

B. DELETE /orders/_doc { "query": { "range": { "amount": { "lt": 100 } } } }

C. POST /orders/_doc/amount_lt_100/_delete

D. POST /orders/_delete_by_query { "query": { "range": { "amount": { "lt": 100 } } } }

Solution

1. Step 1: Identify the correct API for deleting multiple documents by condition

   _delete_by_query is used with POST to delete documents matching a query.

2. Step 2: Check the query for amount less than 100

   The range query with "lt": 100 correctly matches documents with amount less than 100.

3. Step 3: Verify the request method and path

   POST /orders/_delete_by_query with the correct JSON body is the proper syntax.

4. Final Answer:

   POST /orders/_delete_by_query { "query": { "range": { "amount": { "lt": 100 } } } } -> Option D

5. Quick Check:

   Delete by query with range and POST = correct [OK]

Hint: Use POST _delete_by_query with range query for conditional deletes [OK]

Common Mistakes:

• Using DELETE method with request body (not supported)
• Using _doc endpoint instead of _delete_by_query
• Using term query instead of range for less than condition