Read-only transaction

  void 
  
 ReadOnlyTransaction 
 ( 
 google 
 :: 
 cloud 
 :: 
 spanner 
 :: 
 Client 
  
 client 
 ) 
  
 { 
  
 namespace 
  
 spanner 
  
 = 
  
 :: 
 google 
 :: 
 cloud 
 :: 
 spanner 
 ; 
  
 auto 
  
 read_only 
  
 = 
  
 spanner 
 :: 
 MakeReadOnlyTransaction 
 (); 
  
 spanner 
 :: 
 SqlStatement 
  
 select 
 ( 
  
 "SELECT SingerId, AlbumId, AlbumTitle FROM Albums" 
 ); 
  
 using 
  
 RowType 
  
 = 
  
 std 
 :: 
 tuple<std 
 :: 
 int64_t 
 , 
  
 std 
 :: 
 int64_t 
 , 
  
 std 
 :: 
 string 
> ; 
  
 // Read#1. 
  
 auto 
  
 rows1 
  
 = 
  
 client 
 . 
 ExecuteQuery 
 ( 
 read_only 
 , 
  
 select 
 ); 
  
 std 
 :: 
 cout 
 << 
 "Read 1 results 
 \n 
 " 
 ; 
  
 for 
  
 ( 
 auto 
&  
 row 
  
 : 
  
 spanner 
 :: 
 StreamOf<RowType> 
 ( 
 rows1 
 )) 
  
 { 
  
 if 
  
 ( 
 ! 
 row 
 ) 
  
 throw 
  
 std 
 :: 
 move 
 ( 
 row 
 ). 
 status 
 (); 
  
 std 
 :: 
 cout 
 << 
 "SingerId: " 
 << 
 std 
 :: 
 get<0> 
 ( 
 * 
 row 
 ) 
 << 
 " AlbumId: " 
 << 
 std 
 :: 
 get<1> 
 ( 
 * 
 row 
 ) 
 << 
 " AlbumTitle: " 
 << 
 std 
 :: 
 get<2> 
 ( 
 * 
 row 
 ) 
 << 
 " 
 \n 
 " 
 ; 
  
 } 
  
 // Read#2. Even if changes occur in-between the reads the transaction ensures 
  
 // that Read #1 and Read #2 return the same data. 
  
 auto 
  
 rows2 
  
 = 
  
 client 
 . 
 ExecuteQuery 
 ( 
 read_only 
 , 
  
 select 
 ); 
  
 std 
 :: 
 cout 
 << 
 "Read 2 results 
 \n 
 " 
 ; 
  
 for 
  
 ( 
 auto 
&  
 row 
  
 : 
  
 spanner 
 :: 
 StreamOf<RowType> 
 ( 
 rows2 
 )) 
  
 { 
  
 if 
  
 ( 
 ! 
 row 
 ) 
  
 throw 
  
 std 
 :: 
 move 
 ( 
 row 
 ). 
 status 
 (); 
  
 std 
 :: 
 cout 
 << 
 "SingerId: " 
 << 
 std 
 :: 
 get<0> 
 ( 
 * 
 row 
 ) 
 << 
 " AlbumId: " 
 << 
 std 
 :: 
 get<1> 
 ( 
 * 
 row 
 ) 
 << 
 " AlbumTitle: " 
 << 
 std 
 :: 
 get<2> 
 ( 
 * 
 row 
 ) 
 << 
 " 
 \n 
 " 
 ; 
  
 } 
 } 
 

  using 
  
  Google.Cloud.Spanner.Data 
 
 ; 
 using 
  
 System 
 ; 
 using 
  
 System.Collections.Generic 
 ; 
 using 
  
 System.Threading.Tasks 
 ; 
 using 
  
 System.Transactions 
 ; 
 public 
  
 class 
  
 QueryDataWithTransactionAsyncSample 
 { 
  
 public 
  
 class 
  
 Album 
  
 { 
  
 public 
  
 int 
  
 SingerId 
  
 { 
  
 get 
 ; 
  
 set 
 ; 
  
 } 
  
 public 
  
 int 
  
 AlbumId 
  
 { 
  
 get 
 ; 
  
 set 
 ; 
  
 } 
  
 public 
  
 string 
  
 AlbumTitle 
  
 { 
  
 get 
 ; 
  
 set 
 ; 
  
 } 
  
 } 
  
 public 
  
 async 
  
 Task<List<Album> 
>  
 QueryDataWithTransactionAsync 
 ( 
 string 
  
 projectId 
 , 
  
 string 
  
 instanceId 
 , 
  
 string 
  
 databaseId 
 ) 
  
 { 
  
 string 
  
 connectionString 
  
 = 
  
 $"Data Source=projects/{projectId}/instances/{instanceId}/databases/{databaseId}" 
 ; 
  
 var 
  
 albums 
  
 = 
  
 new 
  
 List<Album> 
 (); 
  
 using 
  
 TransactionScope 
  
 scope 
  
 = 
  
 new 
  
 TransactionScope 
 ( 
 TransactionScopeAsyncFlowOption 
 . 
 Enabled 
 ); 
  
 using 
  
 var 
  
 connection 
  
 = 
  
 new 
  
  SpannerConnection 
 
 ( 
 connectionString 
 ); 
  
 // Opens the connection so that the Spanner transaction included in the TransactionScope 
  
 // is read-only TimestampBound.Strong. 
  
 await 
  
 connection 
 . 
  OpenAsync 
 
 ( 
  SpannerTransactionCreationOptions 
 
 . 
  ReadOnly 
 
 , 
  
 options 
 : 
  
 null 
 , 
  
 cancellationToken 
 : 
  
 default 
 ); 
  
 using 
  
 var 
  
 cmd 
  
 = 
  
 connection 
 . 
  CreateSelectCommand 
 
 ( 
 "SELECT SingerId, AlbumId, AlbumTitle FROM Albums" 
 ); 
  
 // Read #1. 
  
 using 
  
 ( 
 var 
  
 reader 
  
 = 
  
 await 
  
 cmd 
 . 
  ExecuteReaderAsync 
 
 ()) 
  
 { 
  
 while 
  
 ( 
 await 
  
 reader 
 . 
  ReadAsync 
 
 ()) 
  
 { 
  
 Console 
 . 
 WriteLine 
 ( 
 "SingerId : " 
  
 + 
  
 reader 
 . 
 GetFieldValue<string> 
 ( 
 "SingerId" 
 ) 
  
 + 
  
 " AlbumId : " 
  
 + 
  
 reader 
 . 
 GetFieldValue<string> 
 ( 
 "AlbumId" 
 ) 
  
 + 
  
 " AlbumTitle : " 
  
 + 
  
 reader 
 . 
 GetFieldValue<string> 
 ( 
 "AlbumTitle" 
 )); 
  
 } 
  
 } 
  
 // Read #2. Even if changes occur in-between the reads, 
  
 // the transaction ensures that Read #1 and Read #2 
  
 // return the same data. 
  
 using 
  
 ( 
 var 
  
 reader 
  
 = 
  
 await 
  
 cmd 
 . 
  ExecuteReaderAsync 
 
 ()) 
  
 { 
  
 while 
  
 ( 
 await 
  
 reader 
 . 
  ReadAsync 
 
 ()) 
  
 { 
  
 albums 
 . 
 Add 
 ( 
 new 
  
 Album 
  
 { 
  
 AlbumId 
  
 = 
  
 reader 
 . 
 GetFieldValue<int> 
 ( 
 "AlbumId" 
 ), 
  
 SingerId 
  
 = 
  
 reader 
 . 
 GetFieldValue<int> 
 ( 
 "SingerId" 
 ), 
  
 AlbumTitle 
  
 = 
  
 reader 
 . 
 GetFieldValue<string> 
 ( 
 "AlbumTitle" 
 ) 
  
 }); 
  
 } 
  
 } 
  
 scope 
 . 
 Complete 
 (); 
  
 Console 
 . 
 WriteLine 
 ( 
 "Transaction complete." 
 ); 
  
 return 
  
 albums 
 ; 
  
 } 
 } 
 

  import 
  
 ( 
  
 "context" 
  
 "fmt" 
  
 "io" 
  
 "cloud.google.com/go/spanner" 
  
 "google.golang.org/api/iterator" 
 ) 
 func 
  
 readOnlyTransaction 
 ( 
 w 
  
 io 
 . 
 Writer 
 , 
  
 db 
  
 string 
 ) 
  
 error 
  
 { 
  
 ctx 
  
 := 
  
 context 
 . 
 Background 
 () 
  
 client 
 , 
  
 err 
  
 := 
  
 spanner 
 . 
 NewClient 
 ( 
 ctx 
 , 
  
 db 
 ) 
  
 if 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 return 
  
 err 
  
 } 
  
 defer 
  
 client 
 . 
 Close 
 () 
  
 ro 
  
 := 
  
 client 
 . 
 ReadOnlyTransaction 
 () 
  
 defer 
  
 ro 
 . 
 Close 
 () 
  
 stmt 
  
 := 
  
 spanner 
 . 
  Statement 
 
 { 
 SQL 
 : 
  
 `SELECT SingerId, AlbumId, AlbumTitle FROM Albums` 
 } 
  
 iter 
  
 := 
  
 ro 
 . 
 Query 
 ( 
 ctx 
 , 
  
 stmt 
 ) 
  
 defer 
  
 iter 
 . 
 Stop 
 () 
  
 for 
  
 { 
  
 row 
 , 
  
 err 
  
 := 
  
 iter 
 . 
 Next 
 () 
  
 if 
  
 err 
  
 == 
  
 iterator 
 . 
 Done 
  
 { 
  
 break 
  
 } 
  
 if 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 return 
  
 err 
  
 } 
  
 var 
  
 singerID 
  
 int64 
  
 var 
  
 albumID 
  
 int64 
  
 var 
  
 albumTitle 
  
 string 
  
 if 
  
 err 
  
 := 
  
 row 
 . 
  Columns 
 
 ( 
& singerID 
 , 
  
& albumID 
 , 
  
& albumTitle 
 ); 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 return 
  
 err 
  
 } 
  
 fmt 
 . 
 Fprintf 
 ( 
 w 
 , 
  
 "%d %d %s\n" 
 , 
  
 singerID 
 , 
  
 albumID 
 , 
  
 albumTitle 
 ) 
  
 } 
  
 iter 
  
 = 
  
 ro 
 . 
 Read 
 ( 
 ctx 
 , 
  
 "Albums" 
 , 
  
 spanner 
 . 
  AllKeys 
 
 (), 
  
 [] 
 string 
 { 
 "SingerId" 
 , 
  
 "AlbumId" 
 , 
  
 "AlbumTitle" 
 }) 
  
 defer 
  
 iter 
 . 
 Stop 
 () 
  
 for 
  
 { 
  
 row 
 , 
  
 err 
  
 := 
  
 iter 
 . 
 Next 
 () 
  
 if 
  
 err 
  
 == 
  
 iterator 
 . 
 Done 
  
 { 
  
 return 
  
 nil 
  
 } 
  
 if 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 return 
  
 err 
  
 } 
  
 var 
  
 singerID 
  
 int64 
  
 var 
  
 albumID 
  
 int64 
  
 var 
  
 albumTitle 
  
 string 
  
 if 
  
 err 
  
 := 
  
 row 
 . 
  Columns 
 
 ( 
& singerID 
 , 
  
& albumID 
 , 
  
& albumTitle 
 ); 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 return 
  
 err 
  
 } 
  
 fmt 
 . 
 Fprintf 
 ( 
 w 
 , 
  
 "%d %d %s\n" 
 , 
  
 singerID 
 , 
  
 albumID 
 , 
  
 albumTitle 
 ) 
  
 } 
 } 
 

  static 
  
 void 
  
 readOnlyTransaction 
 ( 
 DatabaseClient 
  
 dbClient 
 ) 
  
 { 
  
 // ReadOnlyTransaction must be closed by calling close() on it to release resources held by it. 
  
 // We use a try-with-resource block to automatically do so. 
  
 try 
  
 ( 
 ReadOnlyTransaction 
  
 transaction 
  
 = 
  
 dbClient 
 . 
 readOnlyTransaction 
 ()) 
  
 { 
  
 try 
  
 ( 
 ResultSet 
  
 queryResultSet 
  
 = 
  
 transaction 
 . 
 executeQuery 
 ( 
  
 Statement 
 . 
 of 
 ( 
 "SELECT SingerId, AlbumId, AlbumTitle FROM Albums" 
 ))) 
  
 { 
  
 while 
  
 ( 
 queryResultSet 
 . 
 next 
 ()) 
  
 { 
  
 System 
 . 
 out 
 . 
 printf 
 ( 
  
 "%d %d %s\n" 
 , 
  
 queryResultSet 
 . 
 getLong 
 ( 
 0 
 ), 
  
 queryResultSet 
 . 
 getLong 
 ( 
 1 
 ), 
  
 queryResultSet 
 . 
 getString 
 ( 
 2 
 )); 
  
 } 
  
 } 
  
 // queryResultSet.close() is automatically called here 
  
 try 
  
 ( 
 ResultSet 
  
 readResultSet 
  
 = 
  
 transaction 
 . 
 read 
 ( 
  
 "Albums" 
 , 
  
 KeySet 
 . 
 all 
 (), 
  
 Arrays 
 . 
 asList 
 ( 
 "SingerId" 
 , 
  
 "AlbumId" 
 , 
  
 "AlbumTitle" 
 ))) 
  
 { 
  
 while 
  
 ( 
 readResultSet 
 . 
 next 
 ()) 
  
 { 
  
 System 
 . 
 out 
 . 
 printf 
 ( 
  
 "%d %d %s\n" 
 , 
  
 readResultSet 
 . 
 getLong 
 ( 
 0 
 ), 
  
 readResultSet 
 . 
 getLong 
 ( 
 1 
 ), 
  
 readResultSet 
 . 
 getString 
 ( 
 2 
 )); 
  
 } 
  
 } 
  
 // readResultSet.close() is automatically called here 
  
 } 
  
 // transaction.close() is automatically called here 
 } 
 

  // Imports the Google Cloud client library 
 const 
  
 { 
 Spanner 
 } 
  
 = 
  
 require 
 ( 
 ' @google-cloud/spanner 
' 
 ); 
 /** 
 * TODO(developer): Uncomment the following lines before running the sample. 
 */ 
 // const projectId = 'my-project-id'; 
 // const instanceId = 'my-instance'; 
 // const databaseId = 'my-database'; 
 // Creates a client 
 const 
  
 spanner 
  
 = 
  
 new 
  
  Spanner 
 
 ({ 
  
 projectId 
 : 
  
 projectId 
 , 
 }); 
 // Gets a reference to a Cloud Spanner instance and database 
 const 
  
 instance 
  
 = 
  
 spanner 
 . 
 instance 
 ( 
 instanceId 
 ); 
 const 
  
 database 
  
 = 
  
 instance 
 . 
 database 
 ( 
 databaseId 
 ); 
 // Gets a transaction object that captures the database state 
 // at a specific point in time 
 database 
 . 
  getSnapshot 
 
 ( 
 async 
  
 ( 
 err 
 , 
  
 transaction 
 ) 
  
 = 
>  
 { 
  
 if 
  
 ( 
 err 
 ) 
  
 { 
  
 console 
 . 
 error 
 ( 
 err 
 ); 
  
 return 
 ; 
  
 } 
  
 const 
  
 queryOne 
  
 = 
  
 'SELECT SingerId, AlbumId, AlbumTitle FROM Albums' 
 ; 
  
 try 
  
 { 
  
 // Read #1, using SQL 
  
 const 
  
 [ 
 qOneRows 
 ] 
  
 = 
  
 await 
  
 transaction 
 . 
 run 
 ( 
 queryOne 
 ); 
  
 qOneRows 
 . 
 forEach 
 ( 
 row 
  
 = 
>  
 { 
  
 const 
  
 json 
  
 = 
  
 row 
 . 
 toJSON 
 (); 
  
 console 
 . 
 log 
 ( 
  
 `SingerId: 
 ${ 
 json 
 . 
 SingerId 
 } 
 , AlbumId: 
 ${ 
 json 
 . 
 AlbumId 
 } 
 , AlbumTitle: 
 ${ 
 json 
 . 
 AlbumTitle 
 } 
 ` 
 , 
  
 ); 
  
 }); 
  
 const 
  
 queryTwo 
  
 = 
  
 { 
  
 columns 
 : 
  
 [ 
 'SingerId' 
 , 
  
 'AlbumId' 
 , 
  
 'AlbumTitle' 
 ], 
  
 }; 
  
 // Read #2, using the `read` method. Even if changes occur 
  
 // in-between the reads, the transaction ensures that both 
  
 // return the same data. 
  
 const 
  
 [ 
 qTwoRows 
 ] 
  
 = 
  
 await 
  
 transaction 
 . 
 read 
 ( 
 'Albums' 
 , 
  
 queryTwo 
 ); 
  
 qTwoRows 
 . 
 forEach 
 ( 
 row 
  
 = 
>  
 { 
  
 const 
  
 json 
  
 = 
  
 row 
 . 
 toJSON 
 (); 
  
 console 
 . 
 log 
 ( 
  
 `SingerId: 
 ${ 
 json 
 . 
 SingerId 
 } 
 , AlbumId: 
 ${ 
 json 
 . 
 AlbumId 
 } 
 , AlbumTitle: 
 ${ 
 json 
 . 
 AlbumTitle 
 } 
 ` 
 , 
  
 ); 
  
 }); 
  
 console 
 . 
 log 
 ( 
 'Successfully executed read-only transaction.' 
 ); 
  
 } 
  
 catch 
  
 ( 
 err 
 ) 
  
 { 
  
 console 
 . 
 error 
 ( 
 'ERROR:' 
 , 
  
 err 
 ); 
  
 } 
  
 finally 
  
 { 
  
 transaction 
 . 
 end 
 (); 
  
 // Close the database when finished. 
  
 await 
  
 database 
 . 
 close 
 (); 
  
 } 
 }); 
 

  use Google\Cloud\Spanner\SpannerClient; 
 /** 
 * Reads data inside of a read-only transaction. 
 * 
 * Within the read-only transaction, or "snapshot", the application sees 
 * consistent view of the database at a particular timestamp. 
 * Example: 
 * ``` 
 * read_only_transaction($instanceId, $databaseId); 
 * ``` 
 * 
 * @param string $instanceId The Spanner instance ID. 
 * @param string $databaseId The Spanner database ID. 
 */ 
 function read_only_transaction(string $instanceId, string $databaseId): void 
 { 
 $spanner = new SpannerClient(); 
 $instance = $spanner->instance($instanceId); 
 $database = $instance->database($databaseId); 
 $snapshot = $database->snapshot(); 
 $results = $snapshot->execute( 
 'SELECT SingerId, AlbumId, AlbumTitle FROM Albums' 
 ); 
 print('Results from the first read:' . PHP_EOL); 
 foreach ($results as $row) { 
 printf('SingerId: %s, AlbumId: %s, AlbumTitle: %s' . PHP_EOL, 
 $row['SingerId'], $row['AlbumId'], $row['AlbumTitle']); 
 } 
 // Perform another read using the `read` method. Even if the data 
 // is updated in-between the reads, the snapshot ensures that both 
 // return the same data. 
 $keySet = $spanner->keySet(['all' => true]); 
 $results = $database->read( 
 'Albums', 
 $keySet, 
 ['SingerId', 'AlbumId', 'AlbumTitle'] 
 ); 
 print('Results from the second read:' . PHP_EOL); 
 foreach ($results->rows() as $row) { 
 printf('SingerId: %s, AlbumId: %s, AlbumTitle: %s' . PHP_EOL, 
 $row['SingerId'], $row['AlbumId'], $row['AlbumTitle']); 
 } 
 } 
 

  def 
  
 read_only_transaction 
 ( 
 instance_id 
 , 
 database_id 
 ): 
  
 """Reads data inside of a read-only transaction. 
 Within the read-only transaction, or "snapshot", the application sees 
 consistent view of the database at a particular timestamp. 
 """ 
 spanner_client 
 = 
 spanner 
 . 
 Client 
 () 
 instance 
 = 
 spanner_client 
 . 
 instance 
 ( 
 instance_id 
 ) 
 database 
 = 
 instance 
 . 
 database 
 ( 
 database_id 
 ) 
 with 
 database 
 . 
 snapshot 
 ( 
 multi_use 
 = 
 True 
 ) 
 as 
 snapshot 
 : 
 # Read using SQL. 
 results 
 = 
 snapshot 
 . 
 execute_sql 
 ( 
 "SELECT SingerId, AlbumId, AlbumTitle FROM Albums" 
 ) 
 print 
 ( 
 "Results from first read:" 
 ) 
 for 
 row 
 in 
 results 
 : 
 print 
 ( 
 "SingerId: 
 {} 
 , AlbumId: 
 {} 
 , AlbumTitle: 
 {} 
 " 
 . 
 format 
 ( 
 * 
 row 
 )) 
 # Perform another read using the `read` method. Even if the data 
 # is updated in-between the reads, the snapshot ensures that both 
 # return the same data. 
 keyset 
 = 
 spanner 
 . 
 KeySet 
 ( 
 all_ 
 = 
 True 
 ) 
 results 
 = 
 snapshot 
 . 
 read 
 ( 
 table 
 = 
 "Albums" 
 , 
 columns 
 = 
 ( 
 "SingerId" 
 , 
 "AlbumId" 
 , 
 "AlbumTitle" 
 ), 
 keyset 
 = 
 keyset 
 ) 
 print 
 ( 
 "Results from second read:" 
 ) 
 for 
 row 
 in 
 results 
 : 
 print 
 ( 
 "SingerId: 
 {} 
 , AlbumId: 
 {} 
 , AlbumTitle: 
 {} 
 " 
 . 
 format 
 ( 
 * 
 row 
 )) 
 

  # project_id  = "Your Google Cloud project ID" 
 # instance_id = "Your Spanner instance ID" 
 # database_id = "Your Spanner database ID" 
 require 
  
 "google/cloud/spanner" 
 spanner 
  
 = 
  
 Google 
 :: 
 Cloud 
 :: 
  Spanner 
 
 . 
 new 
  
 project 
 : 
  
 project_id 
 client 
  
 = 
  
 spanner 
 . 
  client 
 
  
 instance_id 
 , 
  
 database_id 
 client 
 . 
  snapshot 
 
  
 do 
  
 | 
 snapshot 
 | 
  
 snapshot 
 . 
 execute 
 ( 
 "SELECT SingerId, AlbumId, AlbumTitle FROM Albums" 
 ) 
 . 
 rows 
 . 
  each 
 
  
 do 
  
 | 
 row 
 | 
  
 puts 
  
 " 
 #{ 
 row 
 [ 
 :AlbumId 
 ] 
 } 
  
 #{ 
 row 
 [ 
 :AlbumTitle 
 ] 
 } 
  
 #{ 
 row 
 [ 
 :SingerId 
 ] 
 } 
 " 
  
 end 
  
 # Even if changes occur in-between the reads, the transaction ensures that 
  
 # both return the same data. 
  
 snapshot 
 . 
 read 
 ( 
 "Albums" 
 , 
  
 [ 
 :AlbumId 
 , 
  
 :AlbumTitle 
 , 
  
 :SingerId 
 ] 
 ) 
 . 
 rows 
 . 
  each 
 
  
 do 
  
 | 
 row 
 | 
  
 puts 
  
 " 
 #{ 
 row 
 [ 
 :AlbumId 
 ] 
 } 
  
 #{ 
 row 
 [ 
 :AlbumTitle 
 ] 
 } 
  
 #{ 
 row 
 [ 
 :SingerId 
 ] 
 } 
 " 
  
 end 
 end