Hello everyone,
I am proceeding with my code thank you to this community I’ll never thank you enough 
With your great help, I managed to write a code to: create an asset (with a key), update the asset, retrieve the asset with FetchByKey, then, make a proposal to sell the asset, and finally a contract to sell the asset. I have a question and a problem:
1- In one of the previous topics (Testing fetchByKey - #4 by WallaceKelly) Wallace very kindly suggested that there is no need to copy all instances in the asset, I can just search the asset code. However, I don’t understand if I have to repeat the key and the maintainer in the AssetProposal and in the AssetContract. What is the correct way to keep the chain of the asset, being created, updated, proposed for sale and sold? At the moment I copied the entire Asset.
2- My code doesn’t compile for an issue apparently related to the parties (buyerSolicitor = proposerOwnerSolicitor) and (buyer = proposerOwner). However, everything looks fine to me and I don’t understand where I am wrong.
I copy my code below, hoping that someone will be so kind as to, (again and again 
) help me. I also copied the module Asset (which should be ok) for completeness.
In my defence, I try a lot and a lot before coming back to the community as I am very conscious that you are all busy and my issues are banal for all other people.
module SellAsset where
import Asset
import DA.Time (time)
type AssetProposalId = ContractId AssetProposal
type AssetContractId = ContractId AssetContract
template AssetProposal
with
--idCode : Text
asset: Asset
proposerOwnerSolicitor:Party
proposerOwner:Party
notes: Text
date: Time
where
signatory asset.ownerSolicitor
observer asset.owner, proposerOwner, asset.auctionHouse
-- What the seller can do (through the Owner Solicitor)
-- Propose to sell the asset
choice MakeAssetContractOffer
: AssetProposalId
with
assetproposal : Text
controller asset.ownerSolicitor
do create this
--revise the offer
choice ReviseAsseContractOffer
: AssetProposalId
with
offerRevison :Text
controller asset.ownerSolicitor
do create this with
notes = offerRevison
-- What the buyer can do (through the New Owner Solicitor)
--reject the offer
choice RejectAssetContractOffer
: AssetProposalId
with
feedback : Text
controller proposerOwnerSolicitor
do create this with
notes = feedback
---accept the offer
template AssetContract
with
--idCode: Text
asset : Asset
buyer : Party
seller: Party
buyerSolicitor : Party
sellerSolicitor : Party
contractNotes : Text
contractDate : Time
auctionHouseInContract :Party
where
signatory buyerSolicitor, sellerSolicitor
observer buyer, seller, auctionHouseInContract
choice AcceptContractOffer
: AssetContractId
with
controller buyerSolicitor
do create AssetContract with
asset
buyer = proposerOwner
seller = asset.owner
sellerSolicitor = asset.ownerSolicitor
buyerSolicitor = proposerOwnerSolicitor
contractNotes
contractDate
auctionHouseInContract = asset.auctionHouse
module Asset where
type AssetId = ContractId Asset
template Asset
with
ownerSolicitor : Party
owner : Party
auctionHouse :Party --also makes sure that all parties are legit
address :Text
idCode: Text --To check how to create an asset ID. To be generated offline
a_description : Text
a_documents : [Text]
a_docLink : Text --to be reviwed to create a link to the documents
v_description : Text
v_documents : [Text]
v_docLink : Text --to be reviwed to create a link to the documents
date: Time
where
signatory ownerSolicitor
observer owner,auctionHouse
key (ownerSolicitor, idCode) : (Party, Text)
maintainer key._1
choice UpdateAsset
: ContractId Asset
with
new_owner : Party
new_address :Text
new_a_description : Text
new_a_documents : [Text]
new_a_docLink : Text
new_v_description : Text
new_v_documents : [Text]
new_v_docLink : Text
new_date:Time
controller ownerSolicitor
do
create this with
owner = new_owner
address = new_address
a_description = new_a_description
a_documents = a_documents ++ new_a_documents
a_docLink = new_a_docLink
v_description = new_v_description
v_documents = v_documents ++ new_v_documents
v_docLink = new_v_docLink
date = new_date
template AssetHelper
with
caller : Party
where
signatory caller
choice GetAssetByIdCode : (AssetId, Asset)
with
idCode : Text
controller caller
do
fetchByKey @Asset (caller, idCode)
