Why Indexing a document (POST/PUT) in Elasticsearch? - Purpose & Use Cases

The Big Idea

What if you could find any piece of information instantly without digging through piles of data?

The Scenario

Imagine you have a huge pile of papers with important information, and you want to find a specific detail quickly. Without organizing or labeling them, you have to flip through every page manually.

The Problem

Manually searching or updating information in a large collection is slow and prone to mistakes. You might miss pages, overwrite important data, or waste hours trying to find what you need.

The Solution

Indexing a document with POST or PUT in Elasticsearch automatically organizes your data so you can quickly add, update, or find information without flipping through everything.

Before vs After

✗ Before

curl -XPOST 'http://localhost:9200/myindex/_doc/' -H 'Content-Type: application/json' -d '{"name":"John"}'

✓ After

curl -XPUT 'http://localhost:9200/myindex/_doc/1' -H 'Content-Type: application/json' -d '{"name":"John"}'

What It Enables

It lets you store and update data instantly, making search and retrieval fast and reliable.

Real Life Example

Think of a library adding new books or updating existing ones in its catalog so visitors can find them easily online.

Key Takeaways

Manual data handling is slow and error-prone.

Indexing organizes data for quick access.

POST/PUT commands add or update documents efficiently.

Practice

1. What is the main difference between using POST and PUT when indexing a document in Elasticsearch?

easy

A. POST adds a document with an auto-generated ID, PUT adds or replaces a document with a specified ID.

B. POST deletes a document, PUT updates a document.

C. POST is used only for searching, PUT is used for indexing.

D. POST requires an ID, PUT never requires an ID.

Solution

1. Step 1: Understand POST behavior

   POST indexes a document and Elasticsearch generates a unique ID automatically.

2. Step 2: Understand PUT behavior

   PUT indexes a document with the ID you specify, replacing any existing document with that ID.

3. Final Answer:

   POST adds a document with an auto-generated ID, PUT adds or replaces a document with a specified ID. -> Option A

4. Quick Check:

   Method difference = auto ID vs specified ID [OK]

Hint: Remember: POST auto-IDs, PUT needs your ID [OK]

Common Mistakes:

• Thinking POST deletes documents
• Confusing PUT with search operation
• Assuming PUT never requires an ID

2. Which of the following is the correct syntax to index a document with ID "123" using PUT in Elasticsearch?

easy

A. POST /index/_doc {"field": "value"}

B. POST /index/_doc/123 {"field": "value"}

C. PUT /index/_doc {"field": "value"}

D. PUT /index/_doc/123 {"field": "value"}

Solution

1. Step 1: Identify correct HTTP method and URL

   To specify an ID, use PUT with the URL including the ID: /index/_doc/123.

2. Step 2: Confirm request body format

   The body contains the document fields as JSON, e.g., {"field": "value"}.

3. Final Answer:

   PUT /index/_doc/123 {"field": "value"} -> Option D

4. Quick Check:

   PUT + ID in URL = correct syntax [OK]

Hint: PUT with ID in URL, POST without ID [OK]

Common Mistakes:

• Using POST with an ID in URL
• Omitting the ID when using PUT
• Confusing URL structure

3. Given this request to index a document:

POST /products/_doc
{
  "name": "Coffee Mug",
  "price": 12.99
}

What will Elasticsearch do after this request?

medium

A. Index the document with an auto-generated ID under the 'products' index.

B. Replace any existing document with ID 'products'.

C. Return an error because ID is missing.

D. Create a new index named '_doc'.

Solution

1. Step 1: Analyze the HTTP method and URL

   The request uses POST on /products/_doc, which means index 'products' and type '_doc'.

2. Step 2: Understand ID assignment

   Since no ID is specified, Elasticsearch generates a unique ID automatically and indexes the document.

3. Final Answer:

   Index the document with an auto-generated ID under the 'products' index. -> Option A

4. Quick Check:

   POST without ID = auto-generated ID [OK]

Hint: POST without ID means auto ID assigned [OK]

Common Mistakes:

• Thinking missing ID causes error
• Assuming document replaces existing one
• Confusing index and type names

4. You tried to index a document with PUT /myindex/_doc without specifying an ID. What is the problem with this request?

medium

A. It will create a document with a random ID.

B. It will update all documents in the index.

C. It will cause a syntax error because ID is missing in the URL.

D. It will delete the entire index.

Solution

1. Step 1: Check the HTTP method and URL requirements

   PUT requires an explicit document ID in the URL to index or replace a document.

2. Step 2: Identify the error cause

   Since the ID is missing, Elasticsearch will reject the request with an error due to invalid URL syntax.

3. Final Answer:

   It will cause a syntax error because ID is missing in the URL. -> Option C

4. Quick Check:

   PUT needs ID in URL [OK]

Hint: PUT without ID in URL causes error [OK]

Common Mistakes:

• Assuming PUT auto-generates ID
• Thinking it deletes index
• Believing it updates all documents

5. You want to update a document if it exists or create it if it doesn't, using ID "789" in index "users". Which is the best way to do this in Elasticsearch?

hard

A. Use POST /users/_doc with the document body {"id": "789"}.

B. Use PUT /users/_doc/789 with the document body.

C. Use POST /users/_doc without ID.

D. Use DELETE /users/_doc/789 then POST /users/_doc.

Solution

1. Step 1: Understand update or create behavior

   PUT with a specified ID will create the document if missing or replace it if it exists.

2. Step 2: Compare options

   POST without ID creates new documents with auto IDs, so it won't update by ID. Deleting then posting is inefficient.

3. Final Answer:

   Use PUT /users/_doc/789 with the document body. -> Option B

4. Quick Check:

   PUT with ID updates or creates [OK]

Hint: PUT with ID updates or creates document [OK]

Common Mistakes:

• Specifying ID in the document body
• Omitting ID when update needed
• Deleting before posting wastes resources