transactions Class Reference

The transactions object is used to initiate a transaction. More...

#include <couchbase/transactions.hxx>

Public Member Functions
virtual	~transactions ()=default
virtual auto	run (txn_logic &&logic, const transaction_options &cfg) -> std::pair< error, transaction_result >=0
	Run a blocking transaction.
auto	run (txn_logic &&logic) -> std::pair< error, transaction_result >
virtual void	run (async_txn_logic &&logic, async_txn_complete_logic &&complete_callback, const transaction_options &cfg)=0
	Run an asynchronous transaction.
void	run (async_txn_logic &&logic, async_txn_complete_logic &&complete_callback)

Detailed Description

The transactions object is used to initiate a transaction.

Examples

async_game_server.cxx, and game_server.cxx.

Constructor & Destructor Documentation

~transactions()

virtual ~transactions ( )

virtualdefault

Member Function Documentation

run() [1/4]

void run ( async_txn_logic && logic, async_txn_complete_logic && complete_callback )

inline

run() [2/4]

virtual void run ( async_txn_logic && logic, async_txn_complete_logic && complete_callback, const transaction_options & cfg )

pure virtual

Run an asynchronous transaction.

You can supply a lambda or function which uses a yielded async_attempt_context to perform a transaction, where each transaction operation is asynchronous. A simple usage would be to get 3 document and replace the contents of each. In the example below, we get the 3 documents in parallel, and update each when the get returns the document. This can be significantly faster than getting each document in serial, and updating it using the blocking api:

// [4.1] create promise to retrieve result from the transaction
auto barrier = std::make_shared<std::promise<std::error_code>>();
auto f = barrier->get_future();
cluster.transactions()->run(
  // [4.2] closure argument to run() method encapsulates logic, that has to be run in
  // transaction
  [=](std::shared_ptr<couchbase::transactions::async_attempt_context> ctx) -> couchbase::error {
    // [4.3] get document
    ctx->get(collection, id_1, [=](auto err_ctx_1, auto doc) {
      if (err_ctx_1.ec()) {
        fmt::print(
          stderr, "failed to get document \"{}\": {}\n", id_1, err_ctx_1.ec().message());
        return;
      }
      // [4.4] replace document's content
      ctx->replace(doc,
                   tao::json::value{ { "some", "other async content" } },
                   [=](auto err_ctx_2, auto /*res*/) {
                     if (err_ctx_2.ec()) {
                       fmt::print(stderr,
                                  "error replacing content in doc {}: {}\n",
                                  id_1,
                                  err_ctx_2.ec().message());
                     } else {
                       fmt::print("successfully replaced: {}\n", id_1);
                     }
                   });
    });
    ctx->get(collection, id_2, [=](auto err_ctx_1, auto doc) {
      if (err_ctx_1.ec()) {
        fmt::print("error getting doc {}: {}", id_2, err_ctx_1.ec().message());
        return;
      }
      ctx->replace(doc,
                   tao::json::value{ { "some", "other async content" } },
                   [=](auto err_ctx_2, auto /*res*/) {
                     if (err_ctx_2.ec()) {
                       fmt::print(stderr,
                                  "error replacing content in doc {}: {}\n",
                                  id_2,
                                  err_ctx_2.ec().message());
                     } else {
                       fmt::print("successfully replaced: {}\n", id_2);
                     }
                   });
    });
    ctx->get(collection, id_3, [=](auto err_ctx_1, auto doc) {
      if (err_ctx_1.ec()) {
        fmt::print(stderr, "error getting doc {}: {}\n", id_3, err_ctx_1.ec().message());
        return;
      }
      ctx->replace(doc,
                   tao::json::value{ { "some", "other async content" } },
                   [=](auto err_ctx_2, auto /*res*/) {
                     if (err_ctx_2.ec()) {
                       fmt::print(stderr,
                                  "error replacing content in doc {}: {}\n",
                                  id_3,
                                  err_ctx_2.ec().message());
                     } else {
                       fmt::print("successfully replaced: {}\n", id_3);
                     }
                   });
    });
    return {};
  },
  // [4.5], second closure represents transaction completion logic
  [barrier](auto tx_err, auto tx_res) {
    if (tx_err.ec()) {
      fmt::print(stderr,
                 "error in async transaction {}, {}\n",
                 tx_res.transaction_id,
                 tx_err.ec().message());
    }
    barrier->set_value(tx_err.ec());
  });
if (auto async_err = f.get()) {
  fmt::print(stderr, "received async error from future: message - {}\n", async_err.message());
  retval = 1;
}

Parameters

logic	a lambda or function which uses the yielded async_attempt_context to perform the desired transactional operations.
complete_callback	a lambda or function to which is yielded a {transaction_error_context} and {transaction_result}.
cfg	if passed in, these options override the defaults, or those set in the cluster_options.

run() [3/4]

auto run ( txn_logic && logic ) -> std::pair<error, transaction_result>

inline

run() [4/4]

virtual auto run ( txn_logic && logic, const transaction_options & cfg ) -> std::pair< error, transaction_result >

pure virtual

Run a blocking transaction.

You can supply a lambda or function which uses a yielded attempt_context to perform a transaction, where each transaction operation is blocking. A simple usage would be to get a document and replace the contents:

auto [tx_err, tx_res] = cluster.transactions()->run(
  // [3.1] closure argument to run() method encapsulates logic, that has to be run in
  // transaction
  [=](std::shared_ptr<couchbase::transactions::attempt_context> ctx) -> couchbase::error {
    // [3.2] get document
    auto [err_ctx, doc] = ctx->get(collection, id_1);
    if (err_ctx.ec()) {
      fmt::print(stderr, "failed to get document \"{}\": {}\n", id_1, err_ctx.ec().message());
      // [3.3] don't continue the transaction logic
      return {};
    }
    // [3.4] replace document's content
    ctx->replace(doc, tao::json::value{ { "some", "other content" } });
    return {};
  });
// [3.5] check the overall status of the transaction
if (tx_err.ec()) {
  fmt::print(stderr,
             "error in transaction {}, cause: {}\n",
             tx_err.ec().message(),
             tx_err.cause().has_value() ? tx_err.cause().value().ec().message() : "");
  retval = 1;
} else {
  fmt::print("transaction {} completed successfully\n", tx_res.transaction_id);
}

Parameters

logic	a lambda or function which uses the yielded attempt_context to perform the desired transactional operations.
cfg	if passed in, these options override the defaults, or those set in the cluster_options.

Returns

an error, and a transaction_result representing the results of the transaction.

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The documentation for this class was generated from the following file:

• couchbase/transactions.hxx