---
title: "maxKey"
description: "Returns org.bson.types.MaxKey, which is used in filters for the MongoDB Perspective binding expression."
---

# maxKey

> Returns org.bson.types.MaxKey, which is used in filters for the MongoDB Perspective binding expression.

**This function is used by Ignition's Expression language.**

## Description
## Syntax
`maxKey()`

### Parameters
**None**

### Results
**MaxKey** - A special data type that will match with document fields of the same MaxKey type.

## Example
```py title="Code Snippet"
// In this example, we are querying for weather data documents using the field “elevation”
// In a Perspective MongoDB Binding, the expression below is applied to “value” of
// filter { elevation: “value” }
 
maxKey() // binding will return entire document(s) where maxKey is found
```