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

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	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.
`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`.
`ResultSet`	`read(String table, KeySet keys, Iterable<String> columns, Options.ReadOption... options)`	Reads zero or more rows from a database.
`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`.
`Struct`	`readRow(String table, Key key, Iterable<String> columns)`	Reads a single row from a database, returning `null` if the row does not exist.
`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.
`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.
`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.
`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.
`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`.

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

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.
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

Interface ReadContext