Function json_exists 

pub fn json_exists<'a, L>(left: L, path: &'a str) -> SQLiteSQL<'a>
where
    L: ToSQL<'a, SQLiteValue<'a>>,

Create a JSON field exists condition using json_type

Example

let column = SQL::<SQLiteValue>::raw("metadata");
let condition = json_exists(column, "$.theme");
assert_eq!(condition.sql(), "json_type( metadata , '$.theme') IS NOT NULL");