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 finds 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	String	*Required.* Key in primary data source.
from	LookupData \| LookupSelection	*Required.* Data source or selection for secondary data reference.
as	String \| String[]	The output fields on which to store the looked up data values. For data lookups, this property may be left blank if `from.fields` has been specified (those field names will be used); if `from.fields` has not been specified, `as` must be a string. For selection lookups, this property is optional: if unspecified, looked up values will be stored under a property named for the selection; and if specified, it must correspond to `from.fields`.
default	Any	The default value to use if lookup fails. Default value: `null`

Lookup Data

The secondary data reference (set with from) can be 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	String	*Required.* Key in data to lookup.
fields	String[]	Fields in foreign data or selection 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.

Lookup Selection

The secondary data reference (set with from) can also be a selection parameter name.

Property	Type	Description
param	String	*Required.* Selection parameter name to look up.

Lookup Transform