feat: add handler for burns to the transfer handler [subgraph] (#162)

* feat: add handler for burns to the transfer handler

* fix: update transfer.ts to include the changes.

subgraph/src/transfer.ts

@@ -16,18 +16,21 @@ import {
 } from '../generated/schema';
 
 export function handleTransfer(event: TransferEvent): void {
-    let entity = new Transfer(
+    let transfer = new Transfer(
       event.transaction.hash.concatI32(event.logIndex.toI32())
     );
-    entity.from = event.params.from;
-    entity.to = event.params.to;
-    entity.tokenId = event.params.tokenId;
     
-    entity.blockNumber = event.block.number;
+    const TokenId = event.params.tokenId;
-    entity.blockTimestamp = event.block.timestamp;
-    entity.transactionHash = event.transaction.hash;
     
-    entity.save();
+    transfer.from = event.params.from;
+    transfer.to = event.params.to;
+    transfer.tokenId = TokenId;
+  
+    transfer.blockNumber = event.block.number;
+    transfer.blockTimestamp = event.block.timestamp;
+    transfer.transactionHash = event.transaction.hash;
+  
+    transfer.save();
   
     let token: Token | null;
   
@@ -40,11 +43,16 @@ export function handleTransfer(event: TransferEvent): void {
     }
   
     if (parseInt(event.params.from.toHexString()) !== 0) {
+      if (parseInt(event.params.to.toHexString()) === 0) {
+        // Burn
+        // Remove the entity from storage
+        // Its controllers and owner will be affected.
+        store.remove('Token', TokenId.toString());
+      } else {
         // Transfer
-
         // Load the Token by using its TokenId
         token = Token.load(
-            Bytes.fromByteArray(Bytes.fromBigInt(event.params.tokenId))
+          Bytes.fromByteArray(Bytes.fromBigInt(TokenId))
         );
   
         if (token) {
@@ -59,4 +67,6 @@ export function handleTransfer(event: TransferEvent): void {
           log.error('Unknown token was transferred.', []);
         }
       }
-}
+    }
+  }
+