Macro contains_key 

macro_rules! contains_key {
    ($key:expr) => { ... };
    ($address:expr => $key:expr) => { ... };
}

Checks if a record with this key exists

Usage

use we_cdk::*;

#[action]
fn _constructor() {
    let address = base58!("3NzkzibVRkKUzaRzjUxndpTPvoBzQ3iLng3");

    let result: Boolean = contains_key!("boolean_key");
    let result: Boolean = contains_key!(address => "integer_key");
}