The Metafield resource now stores JSON strings
API
Effective September 18, 2018
You can now create a metafield with a value type of json_string, which allows you to store structured data and access it using Liquid. When retrieving the value of a json_string type Metafield, the data is deserialized to an iterable hash or array.
To learn more about accessing metafields using Liquid, see the metafield object reference.