# AOSPERF04-BP03 Use the flat object type for nested objects
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 Improve efficiency by using flat object types for indexing and querying complex data structures, reducing storage and retrieval overhead. 

 **Level of risk exposed if this best practice is not established:** Medium 

 **Desired outcome**: You use flat object types for indexing and querying complex data structures, which improves the efficiency of your storage and retrieval of nested objects. 

 **Benefits of establishing this best practice:** 
+  **Efficient reads:** Fetching performance is similar to that of a keyword field. 
+  **Memory efficiency:** Storing the entire complex JSON object in one field without indexing all of its subfields reduces the number of fields in an index. 
+  **Space efficiency:** OpenSearch does not create an inverted index for subfields in flat objects, which saves space. 
+  **Compatibility for migration:** You can migrate your data from systems that support similar flat types to OpenSearch. 

## Implementation guidance
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 The flat object field type treats the JSON object as a string, allowing subfield access without indexing for faster lookup and addressing performance concerns. 

 Flat objects are defined in the mapping of an index, either at creation time or by adding a new field that is flat object type. You cannot change an existing field to use flat object. 

### Implementation steps
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+  Create a mapping for your index where issue is of type `flat_object`: 

```
PUT /test-index/
        {
        "mappings": {
        "properties": {
        "issue": {
        "type": "flat_object"
        }
        }
        }
        }
```

## Resources
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+  [Flat object field type](https://opensearch.org/docs/latest/field-types/supported-field-types/flat-object/)