Write to data store using forEach

Question

Hello, I'm trying to write an array of data using foreach in a write to multiple data store entities, but it gives me error without specifying what could be wrong: here is the code and the error: 
 a!forEach( 
 items: pv!getDocuments, 
 expression: { 
 a!entityData( 
 entity: cons!CM_REF_CLAIM_DECLARATION_DOC, 
 data: 'type!{urn:com:appian:types:CM}cm_ref_claim_declaration_doc'( 
 idClaimDeclDoc: index(fv!item, "documentId", null), 
 idDoc: index(fv!item, "documentId", null), 
 idClaimDecl: pv!id_claim_declaration, 
 createdBy: index(fv!item, "documentLoadUser", null), 
 createdOn: index(fv!item, "documentLoadDateTime", null) 
 ) 
 ), 
 if( 
 or( 
 a!isNotNullOrEmpty(fv!item.letterTemplate), 
 a!isNotNullOrEmpty(fv!item.letterCreationDate) 
 ), 
 a!entityData( 
 entity: cons!CM_DSE_LETTER, 
 data: 'type!{urn:com:appian:types:CM}cm_letter'( 
 idClaimDecl: pv!id_claim_declaration, 
 idClaim: pv!claimDeclaration.idClaim, 
 idRisk: pv!claimDeclaration.idRisk, 
 sentDate: index(fv!item, "letterSentDate", null), 
 idDoc: index(fv!item, "documentId", null), 
 createdBy: index(fv!item, "letterCreationUser", null), 
 createdOn: index(fv!item, "letterCreationDate", null), 
 receivedDate: index(fv!item, "documentReceptionDate", null) 
 ) 
 ), 
 {} 
 ), 
 a!entityData( 
 entity: cons!CM_DSE_DOCUMENT, 
 data: 'type!{urn:com:appian:types:CM}cm_document'( 
 idDoc: index(fv!item, "documentId", null), 
 docName: index(fv!item, "docName", null), 
 docDescription: index(fv!item, "documentDescription", null), 
 receiptDate: index(fv!item, "documentReceptionDate", null), 
 uploadedDate: index(fv!item, "documentLoadDateTime", null), 
 uploadOwner: index(fv!item, "documentLoadUser", null), 
 idDocMacroCategory: index(fv!item, "documentIdMacroCategory", null), 
 idDocMicroCategory: index(fv!item, "documentIdMicroCategory", null), 
 status: index(fv!item, "letterStatus", null), 
 sendLetterDate: index(fv!item, "letterSentDate", null), 
 createdBy: index(fv!item, "documentLoadUser", null), 
 createdOn: index(fv!item, "documentLoadDateTime", null), 
 enrichDate: now() 
 ) 
 ) 
 } 
 )

Is the "forEach" a problem? How should I write it then?

Shubham Aware · Answer

Write to Multiple Data Store Entities smart service expects a flat list of a!entityData() - but a!forEach returns an array of arrays (one array per iteration), which breaks the smart service input. use a!flatten(): a!flatten(
a!forEach(
items: pv!getDocuments,
expression: { ... }
)
) and keep {} for the false branch, not null.