• Source Type - choose source  type for the lookup. Can be sObject or Apex. Select "Apex" to use DataProvider.

Available starting from version 5.0

• Field - (available for sObject Source Type) - choose field of Data Source object that will be used to display lookup option items
• Size - (available for sObject Source Type) - limits lookup options list to the specified number of records

Available starting from version 6.0

• Source Object - (available for sObject Source Type) - available for multi-reference lookups only (e.g. Task -> WhatId (Related To ID)).

• This lookup will allow to select objects that are met all the following conditions:
  1. Objects are listed in multi-reference lookup field Data Type property (Setup -> Object Manager -> %Object% -> %Lookup Field%)
  2. Objects are selected as allowed in Settings (Settings -> Objects Settings -> Allowed Objects)

Pre-population can be done like for any other Object field. Pass the Id of the record of Lookup Data Source object as a parameter to the form.

• Parameter name should be equal to API Name of the lookup field (1).
• Parameter value should be an ID or, if lookup is based on another field, use value of this field (2).

• Source Type - choose source  type for the lookup. Can be sObject, Apex or JSON.
• Use sObject Source Type to search for records in Sales Force.

• Source Object - choose source object for the lookup
• Field - choose field that will be used to display lookup option items
• Size - limits lookup options list to the specified number of records
• Default Value - provide default value if needed
• Use Apex Source Type to get lookup using  DataProvider.
• Choose JSON Source Type to build lookup options using JSON array.

• Pass  array of JSON objects of a following format:

[
{"id":"lookupOptionValue", "name":"lookupOptionLabel"},
{"id":"lookupOptionValue2","name":"lookupOptionLabel2"},
{"id":"lookupOptionValue3", "name":"lookupOptionLabel3"}
]

where "lookupOptionValueX" is option value and "lookupOptionLabelX" is label of the lookup option.

To provide Default Value use lookup Option Id (e.g., "lookupOptionValue2", so in example above it will be passed as Default Value). This will result in following:

Data Provider allows to populate lookups/lists with custom data collected in Apex class.

Create an Apex class which implements WR_BPM.FormBuilderService.FormBuilderApiInterface Interface.

Class should have 2 public methods: loadListData, loadLookupData.

See example attached:

Click lookup "Campaign" (4). Select "Apex" Source Type (5) to see "Data Provider" input. Click icon (6) to select the class. Apply it.

Parameters (7) should be passed as a JSON object:

Attached is a form which can be imported to your organization along with the class attached above to see examples of using Data Provider. 

Built-in FormService Data Provider allows to feed JSON data to lookup. Using FormService Data Provider user can build lookup without interaction with database or using Apex code.

Click lookup (8), select "FormService" in "Data Provider" input (9). Fill in "Parameters" input (10).  Pass JSON array of lookup options via Parameters (11):

Here's how lookup looks like in form preview:

Below is example form that can be uploaded to your organization: