Partial updates in Elasticsearch - Mini Project: Build & Apply

Partial updates in Elasticsearch

📖 Scenario: You are managing a collection of books in an Elasticsearch index. Sometimes, you need to update only certain fields of a book without replacing the entire document.

🎯 Goal: Learn how to perform partial updates on documents in Elasticsearch using the _update API.

📋 What You'll Learn

Create an index with a sample book document

Prepare the _update API call for document ID 1

Write a partial update script to change specific fields

Print the update response to verify success

💡 Why This Matters

🌍 Real World

Partial updates let you change only some parts of a document without sending the whole data again. This saves time and bandwidth.

💼 Career

Many jobs working with search engines or databases require updating records efficiently. Knowing partial updates in Elasticsearch is a valuable skill.

1

Create the initial book document

Create an index called library and add a document with ID 1 containing these fields: title as "The Great Gatsby", author as "F. Scott Fitzgerald", and year as 1925.

Elasticsearch

# Use the Elasticsearch index API to create the document
# Your code here

Hint

Use the PUT method with the index name library and document ID 1.

2

Prepare the _update API call

Use the _update API endpoint for document ID 1 with an empty doc object.

Elasticsearch

PUT /library/_doc/1
{
  "title": "The Great Gatsby",
  "author": "F. Scott Fitzgerald",
  "year": 1925
}

# Write the _update API call for document ID 1
# Your code here

Hint

Use the _update API with the document ID 1.

3

Write the partial update to change the year

Use the _update API on the library index and document ID 1 to change the year field to 1926 using the doc parameter.

Elasticsearch

PUT /library/_doc/1
{
  "title": "The Great Gatsby",
  "author": "F. Scott Fitzgerald",
  "year": 1925
}

# Update the year field to 1926
# Your code here

Hint

Inside doc, specify the field year with the new value 1926.

4

Print the update response

Print the response from the update request to confirm the partial update was successful.

Elasticsearch

PUT /library/_doc/1
{
  "title": "The Great Gatsby",
  "author": "F. Scott Fitzgerald",
  "year": 1925
}

POST /library/_update/1
{
  "doc": {
    "year": 1926
  }
}

# Print the update response
# Your code here

Hint

When you run the update command, Elasticsearch returns a JSON response showing "result": "updated" if successful.

Practice

1. What is the main purpose of using partial updates in Elasticsearch?

easy

A. To delete a document completely from the index

B. To create a new document with all fields specified

C. To update only specific fields of a document without replacing the whole document

D. To retrieve documents matching a query

Solution

1. Step 1: Understand partial update concept

   Partial updates allow changing only some fields of a document instead of replacing the entire document.

2. Step 2: Identify the main purpose

   This saves bandwidth and time by sending only the changed fields, not the whole document.

3. Final Answer:

   To update only specific fields of a document without replacing the whole document -> Option C

4. Quick Check:

   Partial update = update some fields only [OK]

Hint: Partial updates change only some fields, not whole document [OK]

Common Mistakes:

• Confusing partial update with document deletion
• Thinking partial update creates new documents
• Believing partial update retrieves documents

2. Which of the following is the correct syntax to perform a partial update on a document with ID '1' in index 'products'?

easy

A. POST /products/_doc/1 { "price": 20 }

B. POST /products/_update/1 { "doc": { "price": 20 } }

C. PUT /products/_update/1 { "price": 20 }

D. GET /products/_update/1 { "doc": { "price": 20 } }

Solution

1. Step 1: Identify correct HTTP method and endpoint

   Partial updates use POST method on the _update API with the document ID.

2. Step 2: Check request body format

   The update body must include a "doc" key with the fields to update.

3. Final Answer:

   POST /products/_update/1 { "doc": { "price": 20 } } -> Option B

4. Quick Check:

   Use POST + _update + doc key [OK]

Hint: Use POST with _update and doc key for partial updates [OK]

Common Mistakes:

• Using GET instead of POST for update
• Omitting the 'doc' key in request body
• Using PUT on _update endpoint incorrectly
• Updating with _doc endpoint instead of _update

3. Given this partial update request on document ID '2' in index 'users':

POST /users/_update/2
{
  "doc": {
    "age": 30
  }
}

If the original document was {"name": "Alice", "age": 25}, what will be the document after the update?

medium

A. {"name": "Alice", "age": 30}

B. {"age": 30}

C. {"name": "Alice"}

D. {"name": "Alice", "age": 25, "updated": true}

Solution

1. Step 1: Understand partial update effect

   The partial update changes only the "age" field to 30, keeping other fields unchanged.

2. Step 2: Apply update to original document

   Original document {"name": "Alice", "age": 25} becomes {"name": "Alice", "age": 30} after update.

3. Final Answer:

   {"name": "Alice", "age": 30} -> Option A

4. Quick Check:

   Partial update changes only specified fields [OK]

Hint: Partial update changes only given fields, others stay same [OK]

Common Mistakes:

• Thinking update replaces whole document
• Assuming fields not in doc are removed
• Adding extra fields not in update request

4. You try this partial update:

POST /orders/_update/5
{
  "doc": {
    "status": "shipped"
  }
}

But you get an error. Which is the most likely cause?

medium

A. The document with ID '5' does not exist in 'orders' index

B. You used GET instead of POST

C. You forgot to include the 'doc' key in the body

D. The 'status' field cannot be updated

Solution

1. Step 1: Check common update errors

   Partial update errors often happen if the document ID does not exist.

2. Step 2: Analyze given request and error cause

   The syntax is correct, so the likely cause is missing document with ID '5'.

3. Final Answer:

   The document with ID '5' does not exist in 'orders' index -> Option A

4. Quick Check:

   Missing document ID causes update error [OK]

Hint: Check if document ID exists before updating [OK]

Common Mistakes:

• Confusing HTTP method errors with missing document
• Assuming all fields are immutable
• Omitting 'doc' key causing syntax errors

5. You want to increase the 'stock' field by 10 in a product document with ID '10' using a partial update. Which request body correctly achieves this?

hard

A. { "update": { "stock": 10 } }

B. { "doc": { "stock": 10 } }

C. { "doc": { "stock": "stock + 10" } }

D. { "script": { "source": "ctx._source.stock += params.count", "params": { "count": 10 } } }

Solution

1. Step 1: Understand increment operation in partial update

   To increase a numeric field, use a script that adds the value to the existing field.

2. Step 2: Identify correct syntax for scripted update

   { "script": { "source": "ctx._source.stock += params.count", "params": { "count": 10 } } } uses the 'script' key with source code to add 10 to 'stock'.

3. Final Answer:

   { "script": { "source": "ctx._source.stock += params.count", "params": { "count": 10 } } } -> Option D

4. Quick Check:

   Use script to increment numeric fields [OK]

Hint: Use script with ctx._source to increment fields [OK]

Common Mistakes:

• Trying to update with doc key using expression string
• Using 'update' key instead of 'doc' or 'script'
• Assigning value directly instead of incrementing