Migrating from DataClient to DataConnection

In this document we describe how to migrate existing code that uses DataClient to use DataConnection.

All examples use the following aliases:

namespace gc = ::google::cloud;
namespace cbt = ::google::cloud::bigtable;

Simple case

cbt::Table OldCode() {
  auto data_client = cbt::MakeDataClient("project-id", "instance-id");
  return cbt::Table(data_client, "table-id");
}
 
cbt::Table UpdatedCode() {
  auto connection = cbt::MakeDataConnection();
  return cbt::Table(
      connection, cbt::TableResource("project-id", "instance-id", "table-id"));
}

Note that the DataConnection is not associated with any resource ids. They are instead packaged as a TableResource and passed as a single object to Table.

Optional configuration

Note that there is only one Table constructor that accepts a DataConnection. All configuration is done via the Options parameter.

Set an application profile id

cbt::Table OldCode() {
  auto data_client = cbt::MakeDataClient("project-id", "instance-id");
  return cbt::Table(data_client, "app-profile-id", "table-id");
}
 
cbt::Table UpdatedCode() {
  auto connection = cbt::MakeDataConnection();
  return cbt::Table(
      connection, cbt::TableResource("project-id", "instance-id", "table-id"),
      gc::Options{}.set<cbt::AppProfileIdOption>("app-profile-id"));
}

Set a custom retry policy

cbt::Table OldCode() {
  auto data_client = cbt::MakeDataClient("project-id", "instance-id");
  return cbt::Table(data_client, "table-id",
                    cbt::LimitedErrorCountRetryPolicy(7));
}
 
cbt::Table UpdatedCode() {
  auto connection = cbt::MakeDataConnection();
  return cbt::Table(connection,
                    cbt::TableResource("project-id", "instance-id", "table-id"),
                    gc::Options{}.set<cbt::DataRetryPolicyOption>(
                        cbt::DataLimitedErrorCountRetryPolicy(7).clone()));
}

The retry, backoff, and idempotency policies are packaged in Options as shared_ptrs, instead of passed by value as variadic parameters to Table(..., Policies&&).

Also note that the retry and backoff policy types have changed. If you defined your own policy, extending RPCRetryPolicy or RPCBackoffPolicy, it will not be compatible with the new types. The new policies do not have a Setup(grpc::ClientContext&) function. This function has not been included because we believe that setting up the grpc::ClientContext...

1. Should not be tied to the retry policies.
2. Is unlikely to be needed by external customers.

If you do need a Setup() feature, please open a feature request explaining your use case, and we will be happy to accommodate you.