Package 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.

  • Method Details

    • 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

    • readAsync

      AsyncResultSet readAsync(String table, KeySet keys, Iterable<String> columns, Options.ReadOption... options)
      Same as read(String, KeySet, Iterable, ReadOption...), but is guaranteed to be non-blocking and will return the results as an AsyncResultSet.

    • 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

    • readUsingIndexAsync

      AsyncResultSet readUsingIndexAsync(String table, String index, KeySet keys, Iterable<String> columns, Options.ReadOption... options)
      Same as readUsingIndex(String, String, KeySet, Iterable, ReadOption...), but is guaranteed to be non-blocking and will return its results as an AsyncResultSet.

    • 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

    • readRowAsync

      com.google.api.core.ApiFuture<Struct> readRowAsync(String table, Key key, Iterable<String> columns)
      Same as readRow(String, Key, Iterable), but is guaranteed to be non-blocking.

    • 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

    • readRowUsingIndexAsync

      com.google.api.core.ApiFuture<Struct> readRowUsingIndexAsync(String table, String index, Key key, Iterable<String> columns)
      Same as readRowUsingIndex(String, String, Key, Iterable), but is guaranteed to be non-blocking.

    • executeQuery

      ResultSet executeQuery(Statement statement, Options.QueryOption... options)
      Executes a query against the database. Can also execute a DML statement with returning clause in a read/write transaction.

      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

    • executeQueryAsync

      AsyncResultSet executeQueryAsync(Statement statement, Options.QueryOption... options)
      Same as executeQuery(Statement, QueryOption...), but is guaranteed to be non-blocking and returns its results as an AsyncResultSet.

    • 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