Object and nested types in Elasticsearch - Step-by-Step Execution

Concept Flow - Object and nested types

Define mapping with object type

↓

Store JSON document with nested objects

↓

Query on object fields

↓

Define mapping with nested type

↓

Store JSON document with nested arrays

↓

Query with nested query to match inner objects

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Return matching documents

This flow shows how Elasticsearch handles object and nested types: defining mappings, storing documents, and querying them differently.

Execution Sample

Elasticsearch

PUT my_index
{
  "mappings": {
    "properties": {
      "user": { "type": "nested" }
    }
  }
}

Defines an index with a nested type field called 'user' to store arrays of objects.

Execution Table

Step	Action	Input/Condition	Result/Output
1	Define mapping with object type	{"properties":{"address":{"type":"object"}}}	Mapping created with 'address' as object type
2	Index document with nested JSON	{"address":{"city":"NY","zip":"10001"}}	Document stored with 'address' object
3	Query on object field	Match 'address.city' = 'NY'	Document returned if city matches
4	Define mapping with nested type	{"properties":{"user":{"type":"nested"}}}	Mapping created with 'user' as nested type
5	Index document with nested array	{"user":[{"name":"Alice","age":30},{"name":"Bob","age":25}]}	Document stored with nested 'user' array
6	Query with nested query	Match 'user.name' = 'Alice' and 'user.age' = 30	Only documents with matching nested object returned
7	Query with simple object query	Match 'user.name' = 'Alice' and 'user.age' = 25	Document returned incorrectly because fields from different nested objects are mixed
8	Exit	No more queries	End of example

💡 Finished showing difference between object and nested types in mapping and querying

Variable Tracker

Variable	Start	After Step 2	After Step 5	Final
Mapping	Empty	{"address": object}	{"address": object, "user": nested}	{"address": object, "user": nested}
Document	None	{"address":{"city":"NY","zip":"10001"}}	{"address":{"city":"NY","zip":"10001"}, "user":[{"name":"Alice","age":30},{"name":"Bob","age":25}]}	Same
Query Result	None	Document returned if city matches	Document returned if nested user matches	Depends on query

Key Moments - 2 Insights

Why does a simple object query on nested fields sometimes return wrong results?

Because nested objects are stored separately, querying nested fields as simple objects can mix values from different nested objects, as shown in step 7 where the document is returned unexpectedly.

What is the main difference between object and nested types in Elasticsearch?

Object type stores JSON objects as a single document, while nested type stores each object in an array as a separate hidden document, enabling precise queries on inner objects (see steps 4-6).

Visual Quiz - 3 Questions

Look at the execution table, at which step is the nested type mapping defined?

A Step 2

B Step 4

C Step 6

D Step 1

💡 Hint

Check the 'Action' column for 'Define mapping with nested type' in the execution_table.

According to the variable tracker, what is the state of 'Document' after step 5?

A Document with address and nested user array

B Empty document

C Only address object stored

D Document with only nested user array

💡 Hint

Look at the 'Document' row under 'After Step 5' in variable_tracker.

If you query 'user.name' = 'Alice' and 'user.age' = 25 with nested type, what happens according to the execution table?

A No document is returned

B Query causes error

C Document is returned

D All documents are returned

💡 Hint

See step 7 in execution_table where simple object query on nested fields returns the document.

Concept Snapshot

Elasticsearch Object and Nested Types:
- Object type stores JSON objects as single documents.
- Nested type stores arrays of objects as separate hidden docs.
- Nested queries allow precise matching inside arrays.
- Use nested type for arrays of objects needing exact inner matches.
- Object type is simpler but can mix inner object fields in queries.

Full Transcript

This visual execution shows how Elasticsearch handles object and nested types. First, we define a mapping with an object type field and store a document with nested JSON. Queries on object fields return documents if the field matches. Then, we define a mapping with a nested type field to store arrays of objects. Documents with nested arrays are stored, and nested queries allow matching specific inner objects precisely. Simple queries on nested fields without nested query fail to match correctly because nested objects are stored separately. The variable tracker shows how mappings and documents evolve. Key moments clarify common confusions about querying nested fields and the difference between object and nested types. The quiz tests understanding of mapping steps, document states, and query results. This helps beginners see step-by-step how Elasticsearch manages complex JSON structures.