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# Resource: Items

# Type: WixDataAggregatePipelineExpressions

# Action: substring

# Link: https://dev.wix.com/docs/sdk/data-items-sdk/data/items/wix-data-aggregate-pipeline-expressions/substring.md

## Description: Extracts a portion of a string expression.

The `substring()` method configures the aggregation pipeline to extract a portion of the specified string expression.

## Schema:

```json
 Method: substring(expression, start, length)
 Description: Extracts a portion of a string expression.  The `substring()` method configures the aggregation pipeline to extract a portion of the specified string expression.
 Method parameters:
   param name:  expression | type: Expression | description:  Expression to extract a substring from. Expression must resolve to a string. Learn more about using [expressions in aggregation pipelines](https://dev.wix.com/docs/sdk/backend-modules/data/items/wix-data-aggregate-pipeline-expressions/introduction.md). 
   param name:  start | type: Expression | description:  Starting position of the substring to extract, specified in zero-based indexing. Expression must resolve to a number. 
   param name:  length | type: Expression | description:  Number of characters to extract from the starting position. Expression must resolve to a number. 
 Return type: REFERENCE<SubstringExpression>

```