MongoDB’s BSON document structure can store array data types. In order to interpret that data for Designer, the user has to decide how they want those multi-value fields to be displayed.
Bson-wise array expansion allows parsing of all the fields of a nested hierarchy in a sub document of a JSON array. During data retrieval, the column value is converted to JSON, and nested columns are flattened based on a JSON parser logic.
To use the Bson-wise expansion feature, select Bson-Expanded Array in the Structure drop-down box.