Partial updates in Elasticsearch - Step-by-Step Execution

Concept Flow - Partial updates

Start with existing document

↓

Receive partial update data

↓

Merge partial data with existing document

↓

Save updated document

↓

End

Partial updates take new data and merge it into an existing document, then save the updated document.

Execution Sample

Elasticsearch

POST /my_index/_update/1
{
  "doc": {
    "age": 30
  }
}

This request updates the document with ID 1 by changing only the 'age' field to 30.

Execution Table

Step	Action	Input Data	Existing Document	Resulting Document
1	Start with existing document	N/A	{"name": "Alice", "age": 25, "city": "NY"}	{"name": "Alice", "age": 25, "city": "NY"}
2	Receive partial update	{"age": 30}	{"name": "Alice", "age": 25, "city": "NY"}	N/A
3	Merge partial update	{"age": 30}	{"name": "Alice", "age": 25, "city": "NY"}	{"name": "Alice", "age": 30, "city": "NY"}
4	Save updated document	N/A	{"name": "Alice", "age": 30, "city": "NY"}	{"name": "Alice", "age": 30, "city": "NY"}
5	End	N/A	N/A	N/A

💡 Partial update applied and document saved successfully.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
existing_document	{"name": "Alice", "age": 25, "city": "NY"}	{"name": "Alice", "age": 25, "city": "NY"}	{"name": "Alice", "age": 30, "city": "NY"}	{"name": "Alice", "age": 30, "city": "NY"}
partial_update	N/A	{"age": 30}	{"age": 30}	{"age": 30}
resulting_document	N/A	N/A	{"name": "Alice", "age": 30, "city": "NY"}	{"name": "Alice", "age": 30, "city": "NY"}

Key Moments - 2 Insights

Why does the partial update only change the 'age' field and not remove other fields?

Because the update merges the new data into the existing document, it only changes specified fields and keeps others intact, as shown in step 3 of the execution_table.

What happens if the partial update includes a new field not in the original document?

The new field is added to the document during the merge step, just like the 'age' field was updated, extending the document without removing existing fields.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the value of 'age' in the resulting document?

A 30

B 25

C null

D Not present

💡 Hint

Check the 'Resulting Document' column at step 3 in the execution_table.

At which step does the document get saved with the updated data?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Look for the 'Save updated document' action in the execution_table.

If the partial update included a new field 'email', when would it appear in the document?

A After step 1

B After step 2

C After step 3

D Never

💡 Hint

New fields appear after merging partial update, see step 3 in execution_table.

Concept Snapshot

Partial updates in Elasticsearch:
Use POST /index/_update/id with {"doc": {...}}.
Only specified fields change; others stay the same.
Merges new data into existing document.
Saves updated document automatically.

Full Transcript

Partial updates in Elasticsearch let you change only some fields of a document without replacing the whole document. The process starts with the existing document. Then, Elasticsearch receives the partial update data. It merges this data into the existing document, changing or adding only the specified fields. Finally, it saves the updated document. For example, updating the 'age' field from 25 to 30 keeps other fields like 'name' and 'city' unchanged. This merging behavior ensures efficient updates without losing data.

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