cloud.google.com/go/spanner (go): Package spanner provides a client for reading and writing to Cloud Spanner databases. See the packages under admin for clients that operate on databases and instances.  See https://cloud.google.com/spanner/docs/getting-started/go/ for an introduction to Cloud Spanner and additional help on using this API.  See https://godoc.org/cloud.google.com/go for authentication, timeouts, connection pooling and similar aspects of this package.  To start working with this package, create a client that refers to the database of interest:  Remember to close the client after use to free up the sessions in the session pool.  To use an emulator with this library, you can set the SPANNER_EMULATOR_HOST environment variable to the address at which your emulator is running. This will send requests to that address instead of to Cloud Spanner. You can then create and use a client as usual:  Two Client methods, Apply and Single, work well for simple reads and writes. As a quick introduction, here we write a new row to the database and read it back:  All the methods used above are discussed in more detail below.  Every Cloud Spanner row has a unique key, composed of one or more columns. Construct keys with a literal of type Key:  The keys of a Cloud Spanner table are ordered. You can specify ranges of keys using the KeyRange type:  By default, a KeyRange includes its start key but not its end key. Use the Kind field to specify other boundary conditions:  A KeySet represents a set of keys. A single Key or KeyRange can act as a KeySet. Use the KeySets function to build the union of several KeySets:  AllKeys returns a KeySet that refers to all the keys in a table:  All Cloud Spanner reads and writes occur inside transactions. There are two types of transactions, read-only and read-write. Read-only transactions cannot change the database, do not acquire locks, and may access either the current database state or states in the past. Read-write transactions can read the database before writing to it, and always apply to the most recent database state.  The simplest and fastest transaction is a ReadOnlyTransaction that supports a single read operation. Use Client.Single to create such a transaction. You can chain the call to Single with a call to a Read method.  When you only want one row whose key you know, use ReadRow. Provide the table name, key, and the columns you want to read:  Read multiple rows with the Read method. It takes a table name, KeySet, and list of columns:  Read returns a RowIterator. You can call the Do method on the iterator and pass a callback:  RowIterator also follows the standard pattern for the Google Cloud Client Libraries:  Always call Stop when you finish using an iterator this way, whether or not you iterate to the end. (Failing to call Stop could lead you to exhaust the database's session quota.)  To read rows with an index, use ReadUsingIndex.  The most general form of reading uses SQL statements. Construct a Statement with NewStatement, setting any parameters using the Statement's Params map:  You can also construct a Statement directly with a struct literal, providing your own map of parameters.  Use the Query method to run the statement and obtain an iterator:  Once you have a Row, via an iterator or a call to ReadRow, you can extract column values in several ways. Pass in a pointer to a Go variable of the appropriate type when you extract a value.  You can extract by column position or name:  You can extract all the columns at once:  Or you can define a Go struct that corresponds to your columns, and extract into that:  For Cloud Spanner columns that may contain NULL, use one of the NullXXX types, like NullString:  To perform more than one read in a transaction, use ReadOnlyTransaction:  You must call Close when you are done with the transaction.  Cloud Spanner read-only transactions conceptually perform all their reads at a single moment in time, called the transaction's read timestamp. Once a read has started, you can call ReadOnlyTransaction's Timestamp method to obtain the read timestamp.  By default, a transaction will pick the most recent time (a time where all previously committed transactions are visible) for its reads. This provides the freshest data, but may involve some delay. You can often get a quicker response if you are willing to tolerate "stale" data. You can control the read timestamp selected by a transaction by calling the WithTimestampBound method on the transaction before using it. For example, to perform a query on data that is at most one minute stale, use  See the documentation of TimestampBound for more details.  To write values to a Cloud Spanner database, construct a Mutation. The spanner package has functions for inserting, updating and deleting rows. Except for the Delete methods, which take a Key or KeyRange, each mutation-building function comes in three varieties.  One takes lists of columns and values along with the table name:  One takes a map from column names to values:  And the third accepts a struct value, and determines the columns from the struct field names:  To apply a list of mutations to the database, use Apply:  If you need to read before writing in a single transaction, use a ReadWriteTransaction. ReadWriteTransactions may be aborted automatically by the backend and need to be retried. You pass in a function to ReadWriteTransaction, and the client will handle the retries automatically. Use the transaction's BufferWrite method to buffer mutations, which will all be executed at the end of the transaction:  Cloud Spanner STRUCT (aka STRUCT) values (https://cloud.google.com/spanner/docs/data-types#struct-type) can be represented by a Go struct value.  A proto StructType is built from the field types and field tag information of the Go struct. If a field in the struct type definition has a "spanner:<field_name>" tag, then the value of the "spanner" key in the tag is used as the name for that field in the built StructType, otherwise the field name in the struct definition is used. To specify a field with an empty field name in a Cloud Spanner STRUCT type, use the `spanner:""` tag annotation against the corresponding field in the Go struct's type definition.  A STRUCT value can contain STRUCT-typed and Array-of-STRUCT typed fields and these can be specified using named struct-typed and []struct-typed fields inside a Go struct. However, embedded struct fields are not allowed. Unexported struct fields are ignored.  NULL STRUCT values in Cloud Spanner are typed. A nil pointer to a Go struct value can be used to specify a NULL STRUCT value of the corresponding StructType.  Nil and empty slices of a Go STRUCT type can be used to specify NULL and empty array values respectively of the corresponding StructType. A slice of pointers to a Go struct type can be used to specify an array of NULL-able STRUCT values.  Spanner supports DML statements like INSERT, UPDATE and DELETE. Use ReadWriteTransaction.Update to run DML statements. It returns the number of rows affected. (You can call use ReadWriteTransaction.Query with a DML statement. The first call to Next on the resulting RowIterator will return iterator.Done, and the RowCount field of the iterator will hold the number of affected rows.)  For large databases, it may be more efficient to partition the DML statement. Use client.PartitionedUpdate to run a DML statement in this way. Not all DML statements can be partitioned.  This client has been instrumented to use OpenCensus tracing (http://opencensus.io). To enable tracing, see "Enabling Tracing for a Program" at https://godoc.org/go.opencensus.io/trace. OpenCensus tracing requires Go 1.8 or higher.
Keywords: cloud-bigquery|cloud-datastore|cloud-pubsub|cloud-storage|go|golang|google-cloud