add nft.orderCount (#332)

schema.graphql

@@ -100,6 +100,9 @@ type Nft @entity{
     tx: String!   
     "block number when it was created"                                            
     block: Int  
+
+    "number of orders executed for all underlying datatokens"                                
+    orderCount: BigInt!                                              
 }
 
 type Pool @entity {

src/mappings/erc20Templates.ts

@@ -1,4 +1,4 @@
-import { Order } from '../@types/schema'
+import { Order, Nft } from '../@types/schema'
 import { BigInt } from '@graphprotocol/graph-ts'
 import {
   NewPaymentCollector,
@@ -60,6 +60,13 @@ export function handleOrderStarted(event: OrderStarted): void {
   order.save()
   token.save()
   addOrder()
+  if (token.nft) {
+    const nft = Nft.load(token.nft as string) as Nft
+    if (nft) {
+      nft.orderCount = nft.orderCount.plus(integer.ONE)
+      nft.save()
+    }
+  }
 }
 
 export function handleNewPaymentCollector(event: NewPaymentCollector): void {}

src/mappings/nftUpdate.ts

@@ -17,6 +17,7 @@ export function handleCreated(event: MetadataCreated): void {
 
   nft.assetState = event.params.state
   nft.providerUrl = event.params.decryptorUrl.toString()
+
   const nftUpdate = new NftUpdate(
     getId(event.transaction.hash.toHex(), nftAddress)
   )