com.google.cloud.spanner

Interface ReadContext

All Superinterfaces:

AutoCloseable

All Known Subinterfaces:

BatchReadOnlyTransaction, ReadOnlyTransaction, TransactionContext

public interface ReadContext
extends AutoCloseable

A concurrency context in which to run a read or SQL statement. All ReadContexts are implicitly bound to a Session and therefore a particular Database.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	ReadContext.QueryAnalyzeMode Used to specify the mode in which the query should be analyzed by analyzeQuery(Statement,QueryAnalyzeMode).

Method Summary

Modifier and Type	Method and Description
ResultSet	analyzeQuery(Statement statement, ReadContext.QueryAnalyzeMode queryMode) Analyzes a query and returns query plan and/or query execution statistics information.
void	close() Closes this read context and frees up the underlying resources.
ResultSet	executeQuery(Statement statement, Options.QueryOption... options) Executes a query against the database.
ResultSet	read(String table, KeySet keys, Iterable<String> columns, Options.ReadOption... options) Reads zero or more rows from a database.
Struct	readRow(String table, Key key, Iterable<String> columns) Reads a single row from a database, returning null if the row does not exist.
Struct	readRowUsingIndex(String table, String index, Key key, Iterable<String> columns) Reads a single row from a database using an index, returning null if the row does not exist.
ResultSet	readUsingIndex(String table, String index, KeySet keys, Iterable<String> columns, Options.ReadOption... options) Reads zero or more rows from a database using an index.

Method Detail

read

ResultSet read(String table,
               KeySet keys,
               Iterable<String> columns,
               Options.ReadOption... options)

Reads zero or more rows from a database.

Implementations may or may not block in the initial read(...) call; for those that do not, the remote call will be initiated immediately but blocking on the response is deferred to the first ResultSet.next() call. Regardless of blocking behavior, any SpannerException is deferred to the first or subsequent ResultSet.next() call.

 ReadContext readContext = dbClient.singleUse();
 ResultSet resultSet =
     readContext.read(
         "Albums",
         // KeySet.all() can be used to read all rows in a table. KeySet exposes other
         // methods to read only a subset of the table.
         KeySet.all(),
         Arrays.asList("SingerId", "AlbumId", "AlbumTitle"));
 

Parameters:

table - the name of the table to read

keys - the keys and ranges of rows to read. Regardless of ordering in keys, rows are returned in their natural key order.

columns - the columns to read

options - the options to configure the read

readUsingIndex

ResultSet readUsingIndex(String table,
                         String index,
                         KeySet keys,
                         Iterable<String> columns,
                         Options.ReadOption... options)

Reads zero or more rows from a database using an index.

Implementations may or may not block in the initial read(...) call; for those that do not, the remote call will be initiated immediately but blocking on the response is deferred to the first ResultSet.next() call. Regardless of blocking behavior, any SpannerException is deferred to the first or subsequent ResultSet.next() call.

 ReadContext readContext = dbClient.singleUse();
 Struct row =
     readContext.readRowUsingIndex("Albums", "AlbumsByAlbumId", Key.of(1, "Green"),
         Arrays.asList("AlbumId", "AlbumTitle"));
 

Parameters:

table - the name of the table to read

index - the name of the index on table to use

keys - the keys and ranges of index rows to read. Regardless of ordering in keys, rows are returned in the natural key order of the index.

columns - the columns to read

options - the options to configure the read

readRow

@Nullable
Struct readRow(String table,
                         Key key,
                         Iterable<String> columns)

Reads a single row from a database, returning null if the row does not exist.

 ReadContext readContext = dbClient.singleUse();
 Struct row =
     readContext.readRow("Albums", Key.of(2, 1), Arrays.asList("MarketingBudget"));
 

Parameters:

table - the name of the table to read

key - the row to read

columns - the columns to return

readRowUsingIndex

@Nullable
Struct readRowUsingIndex(String table,
                                   String index,
                                   Key key,
                                   Iterable<String> columns)

Reads a single row from a database using an index, returning null if the row does not exist.

 ReadContext readContext = dbClient.singleUse();
 Struct row =
     readContext.readRowUsingIndex("Albums", "AlbumsByAlbumId", Key.of(1, "Green"),
         Arrays.asList("AlbumId", "AlbumTitle"));
 

Parameters:

table - the name of the table to read

index - the name of the index on table to use

key - the index row to read

columns - the columns to return

executeQuery

ResultSet executeQuery(Statement statement,
                       Options.QueryOption... options)

Executes a query against the database.

Implementations may or may not block in the initial executeQuery(...) call; for those that do not, the remote call will be initiated immediately but blocking on the response is deferred to the first ResultSet.next() call. Regardless of blocking behavior, any SpannerException is deferred to the first or subsequent ResultSet.next() call.

 // Rows without an explicit value for MarketingBudget will have a MarketingBudget equal to
 // null.
 ReadContext readContext = dbClient.singleUse();
 ResultSet resultSet =
     readContext.executeQuery(
         Statement.of(
             "SELECT SingerId, AlbumId, MarketingBudget, LastUpdateTime FROM Albums"));
 

Parameters:

statement - the query statement to execute

options - the options to configure the query

analyzeQuery

ResultSet analyzeQuery(Statement statement,
                       ReadContext.QueryAnalyzeMode queryMode)

Analyzes a query and returns query plan and/or query execution statistics information.

The query plan and query statistics information is contained in ResultSetStats that can be accessed by calling ResultSet.getStats() on the returned ResultSet.

 ReadContext rc = dbClient.singleUse();
 ResultSet resultSet =
     rc.analyzeQuery(
         Statement.of("SELECT SingerId, AlbumId, MarketingBudget FROM Albums"),
         ReadContext.QueryAnalyzeMode.PROFILE);
 while (resultSet.next()) {
   // Discard the results. We're only processing because getStats() below requires it.
   resultSet.getCurrentRowAsStruct();
 }
 ResultSetStats stats = resultSet.getStats();
 

Parameters:

statement - the query statement to execute

queryMode - the mode in which to execute the query

close

void close()

Closes this read context and frees up the underlying resources.

Specified by:

close in interface AutoCloseable