Lookup Transform

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The lookup transform extends a primary data source by looking up values from another data source. It is similar to a one sided join.

// Any View Specification
{
  ...
  "transform": [
    {"lookup": ..., "from" ..., "as": ..., "default": ...} // Lookup Transform
     ...
  ],
  ...
}

Lookup Transform

For each data object in the main data source, the transform tries to find a matching objects in the secondary data source. An object matches if the value in the field specified by lookup is the same as the field specified in the from.key.

Property	Type	Description
lookup	FieldName	*Required.* Key in primary data source.
from	LookupData	*Required.* Secondary data reference.
as	FieldName \| FieldName[]	The field or fields for storing the computed formula value. If `from.fields` is specified, the transform will use the same names for `as`. If `from.fields` is not specified, `as` has to be a string and we put the whole object into the data under the specified name.
default	String	The default value to use if lookup fails. Default value: `null`

Lookup Data

The secondary data reference (set with from) is an object that specifies how the lookup key should be matched to a second data source and what fields should be added.

Property	Type	Description
data	Data	*Required.* Secondary data source to lookup in.
key	FieldName	*Required.* Key in data to lookup.
fields	FieldName[]	Fields in foreign data to lookup. If not specified, the entire object is queried.

Example

This example uses lookup to add the properties age and height to the main data source. The person field in the main data source is matched to the name field in the secondary data source.