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    Update

    Use an update in a transaction.

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    For detailed documentation that includes this code sample, see the following:

    Code sample

    C#

    To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries . For more information, see the Datastore mode C# API reference documentation .

    To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment .

      private 
  
 void 
  
 TransferFunds 
 ( 
 Key 
  
 fromKey 
 , 
  
 Key 
  
 toKey 
 , 
  
 long 
  
 amount 
 ) 
 { 
  
 using 
  
 ( 
 var 
  
 transaction 
  
 = 
  
 _db 
 . 
 BeginTransaction 
 ()) 
  
 { 
  
 var 
  
 entities 
  
 = 
  
 transaction 
 . 
 Lookup 
 ( 
 fromKey 
 , 
  
 toKey 
 ); 
  
 entities 
 [ 
 0 
 ][ 
 "balance" 
 ]. 
 IntegerValue 
  
 -= 
  
 amount 
 ; 
  
 entities 
 [ 
 1 
 ][ 
 "balance" 
 ]. 
 IntegerValue 
  
 += 
  
 amount 
 ; 
  
 transaction 
 . 
 Update 
 ( 
 entities 
 ); 
  
 transaction 
 . 
 Commit 
 (); 
  
 } 
 }

    Go

    To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries . For more information, see the Datastore mode Go API reference documentation .

    To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment .

      type 
  
 BankAccount 
  
 struct 
  
 { 
  
 Balance 
  
 int 
 } 
 const 
  
 amount 
  
 = 
  
 50 
 keys 
  
 := 
  
 [] 
 * 
 datastore 
 . 
 Key 
 { 
 to 
 , 
  
 from 
 } 
 tx 
 , 
  
 err 
  
 := 
  
 client 
 . 
 NewTransaction 
 ( 
 ctx 
 ) 
 if 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 log 
 . 
 Fatalf 
 ( 
 "client.NewTransaction: %v" 
 , 
  
 err 
 ) 
 } 
 accs 
  
 := 
  
 make 
 ([] 
 BankAccount 
 , 
  
 2 
 ) 
 if 
  
 err 
  
 := 
  
 tx 
 . 
 GetMulti 
 ( 
 keys 
 , 
  
 accs 
 ); 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 tx 
 . 
 Rollback 
 () 
  
 log 
 . 
 Fatalf 
 ( 
 "tx.GetMulti: %v" 
 , 
  
 err 
 ) 
 } 
 accs 
 [ 
 0 
 ]. 
 Balance 
  
 += 
  
 amount 
 accs 
 [ 
 1 
 ]. 
 Balance 
  
 -= 
  
 amount 
 if 
  
 _ 
 , 
  
 err 
  
 := 
  
 tx 
 . 
 PutMulti 
 ( 
 keys 
 , 
  
 accs 
 ); 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 tx 
 . 
 Rollback 
 () 
  
 log 
 . 
 Fatalf 
 ( 
 "tx.PutMulti: %v" 
 , 
  
 err 
 ) 
 } 
 if 
  
 _ 
 , 
  
 err 
  
 = 
  
 tx 
 . 
 Commit 
 (); 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 log 
 . 
 Fatalf 
 ( 
 "tx.Commit: %v" 
 , 
  
 err 
 ) 
 }

    Java

    To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries . For more information, see the Datastore mode Java API reference documentation .

    To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment .

      void 
  
 transferFunds 
 ( 
 Key 
  
 fromKey 
 , 
  
 Key 
  
 toKey 
 , 
  
 long 
  
 amount 
 ) 
  
 { 
  
 Transaction 
  
 txn 
  
 = 
  
 datastore 
 . 
 newTransaction 
 (); 
  
 try 
  
 { 
  
 List<Entity> 
  
 entities 
  
 = 
  
 txn 
 . 
 fetch 
 ( 
 fromKey 
 , 
  
 toKey 
 ); 
  
 Entity 
  
 from 
  
 = 
  
 entities 
 . 
 get 
 ( 
 0 
 ); 
  
 Entity 
  
 updatedFrom 
  
 = 
  
 Entity 
 . 
 newBuilder 
 ( 
 from 
 ). 
 set 
 ( 
 "balance" 
 , 
  
 from 
 . 
 getLong 
 ( 
 "balance" 
 ) 
  
 - 
  
 amount 
 ). 
 build 
 (); 
  
 Entity 
  
 to 
  
 = 
  
 entities 
 . 
 get 
 ( 
 1 
 ); 
  
 Entity 
  
 updatedTo 
  
 = 
  
 Entity 
 . 
 newBuilder 
 ( 
 to 
 ). 
 set 
 ( 
 "balance" 
 , 
  
 to 
 . 
 getLong 
 ( 
 "balance" 
 ) 
  
 + 
  
 amount 
 ). 
 build 
 (); 
  
 txn 
 . 
 put 
 ( 
 updatedFrom 
 , 
  
 updatedTo 
 ); 
  
 txn 
 . 
 commit 
 (); 
  
 } 
  
 finally 
  
 { 
  
 if 
  
 ( 
 txn 
 . 
 isActive 
 ()) 
  
 { 
  
 txn 
 . 
 rollback 
 (); 
  
 } 
  
 } 
 }

    Node.js

    To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries . For more information, see the Datastore mode Node.js API reference documentation .

    To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment .

      async 
  
 function 
  
 transferFunds 
 ( 
 fromKey 
 , 
  
 toKey 
 , 
  
 amount 
 ) 
  
 { 
  
 const 
  
 transaction 
  
 = 
  
 datastore 
 . 
 transaction 
 (); 
  
 await 
  
 transaction 
 . 
 run 
 (); 
  
 const 
  
 results 
  
 = 
  
 await 
  
 Promise 
 . 
 all 
 ([ 
  
 transaction 
 . 
 get 
 ( 
 fromKey 
 ), 
  
 transaction 
 . 
 get 
 ( 
 toKey 
 ), 
  
 ]); 
  
 const 
  
 accounts 
  
 = 
  
 results 
 . 
 map 
 ( 
 result 
  
 = 
>  
 result 
 [ 
 0 
 ]); 
  
 accounts 
 [ 
 0 
 ]. 
 balance 
  
 -= 
  
 amount 
 ; 
  
 accounts 
 [ 
 1 
 ]. 
 balance 
  
 += 
  
 amount 
 ; 
  
 transaction 
 . 
 save 
 ([ 
  
 { 
  
 key 
 : 
  
 fromKey 
 , 
  
 data 
 : 
  
 accounts 
 [ 
 0 
 ], 
  
 }, 
  
 { 
  
 key 
 : 
  
 toKey 
 , 
  
 data 
 : 
  
 accounts 
 [ 
 1 
 ], 
  
 }, 
  
 ]); 
  
 return 
  
 await 
  
 transaction 
 . 
 commit 
 (); 
 }

    PHP

    To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries . For more information, see the Datastore mode PHP API reference documentation .

    To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment .

      /** 
 * Update two entities in a transaction. 
 * 
 * @param string $fromKeyId 
 * @param string $toKeyId 
 * @param int $amount 
 * @param string $namespaceId 
 */ 
 function transfer_funds( 
 string $fromKeyId, 
 string $toKeyId, 
 int $amount, 
 string $namespaceId = null 
 ) { 
 $datastore = new DatastoreClient(['namespaceId' => $namespaceId]); 
 $transaction = $datastore->transaction(); 
 $fromKey = $datastore->key('Account', $fromKeyId); 
 $toKey = $datastore->key('Account', $toKeyId); 
 // The option 'sort' is important here, otherwise the order of the result 
 // might be different from the order of the keys. 
 $result = $transaction->lookupBatch([$fromKey, $toKey], ['sort' => true]); 
 if (count($result['found']) != 2) { 
 $transaction->rollback(); 
 } 
 $fromAccount = $result['found'][0]; 
 $toAccount = $result['found'][1]; 
 $fromAccount['balance'] -= $amount; 
 $toAccount['balance'] += $amount; 
 $transaction->updateBatch([$fromAccount, $toAccount]); 
 $transaction->commit(); 
 }

    Python

    To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries . For more information, see the Datastore mode Python API reference documentation .

    To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment .

      from 
  
 google.cloud 
  
 import 
  datastore 
 
 # For help authenticating your client, visit 
 # https://cloud.google.com/docs/authentication/getting-started 
 client 
 = 
  datastore 
 
 . 
  Client 
 
 () 
 def 
  
 transfer_funds 
 ( 
 client 
 , 
 from_key 
 , 
 to_key 
 , 
 amount 
 ): 
 with 
 client 
 . 
  transaction 
 
 (): 
 from_account 
 = 
 client 
 . 
  get 
 
 ( 
 from_key 
 ) 
 to_account 
 = 
 client 
 . 
  get 
 
 ( 
 to_key 
 ) 
 from_account 
 [ 
 "balance" 
 ] 
 -= 
 amount 
 to_account 
 [ 
 "balance" 
 ] 
 += 
 amount 
 client 
 . 
  put_multi 
 
 ([ 
 from_account 
 , 
 to_account 
 ])

    Ruby

    To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries . For more information, see the Datastore mode Ruby API reference documentation .

    To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment .

      def 
  
 transfer_funds 
  
 from_key 
 , 
  
 to_key 
 , 
  
 amount 
  
 datastore 
 . 
 transaction 
  
 do 
  
 | 
 tx 
 | 
  
 from 
  
 = 
  
 tx 
 . 
 find 
  
 from_key 
  
 from 
 [ 
 "balance" 
 ] 
  
 -= 
  
 amount 
  
 to 
  
 = 
  
 tx 
 . 
 find 
  
 to_key 
  
 to 
 [ 
 "balance" 
 ] 
  
 += 
  
 amount 
  
 tx 
 . 
 save 
  
 from 
 , 
  
 to 
  
 end 
 end

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