This PR adds support for .transaction()

README.md

@@ -220,6 +220,25 @@ async function main() {
   );
 ```
 
+### Using managed transaction
+
+When using a promise pool, MySQL2 offers a .transaction() function to allow you to execute code within a transaction, with pre-defined behavior to roll back the transaction on error, and which automatically releases the connection after you are finished working with it:
+```js
+async function main() {
+  // get the client
+  const mysql = require('mysql2/promise');
+  // create the pool
+  const pool = mysql.createPool({host:'localhost', user: 'root', database: 'test'});
+  // using the pool, execute a chain of queries within a transaction
+  pool.transaction({ autoCommit: false, readWrite: true, consistentSnapshot: false }, async function(con) {
+    const [rows, fields] = await con.query('SELECT * FROM `table` WHERE `name` = ? AND `age` > ?', ['Morty', 14]);
+    await con.execute('INSERT INTO `table` (name,age) VALUES(?,?)', ['Bob',rows[0].age]); // Bob and Morty are the same age
+  });
+  // If the promise chain passed to .transaction() resolves, .transaction() commits the changes, and releases the connection.
+  // If the promise chain passed to .transaction() rejects, or if a connection or SQL error occures, .transaction() rolls back the changes, and releases the connection.
+}
+```
+
 ## API and Configuration
 
 MySQL2 is mostly API compatible with [Node MySQL][node-mysql]. You should check their API documentation to see all available API options.

promise.js

@@ -214,6 +214,47 @@ PromiseConnection.prototype.changeUser = function(options) {
     });
   });
 };
+PromiseConnection.prototype.transaction = function(options,userPromise) {
+  const self = this;
+  if (! userPromise) {
+   userPromise = options;
+   options = {};
+  }
+  options = options || {};
+
+  var promiseChain = Promise.resolve();
+
+  if (options.autoCommit !== true) {
+    promiseChain = promiseChain.then(function() {
+      return self.query(
+        "START TRANSACTION" +
+        ( options.consistentSnapshot === true ? " WITH CONSISTENT SNAPSHOT" : 
+         ( options.readWrite !== false ? " READ WRITE" : " READ ONLY" )
+        )
+      );
+    });
+  }
+
+  promiseChain = promiseChain.then(function() {
+    return userPromise(self);
+  });
+
+  if (options.autoCommit === false) {
+    promiseChain = promiseChain.then(function(res) {
+      return self.query("COMMIT")
+      .then(function() {
+        return res;
+      });
+    })
+    .catch(function(err) {
+      return self.query("ROLLBACK")
+      .catch(function() {
+        throw err;
+      });
+    })
+  }
+  return promiseChain;
+};
 
 function PromisePreparedStatementInfo(statement, promiseImpl) {
   this.statement = statement;
@@ -339,6 +380,21 @@ PromisePool.prototype.getConnection = function() {
   });
 };
 
+PromisePool.prototype.transaction = function(options,userPromise) {
+  return this.getConnection()
+  .then(function(con) {
+    return this.Promise.resolve(con.transaction(options,userPromise))
+    .then(function(res) {
+      con.release();
+      return res;
+    })
+    .catch(function(err) {
+      con.release();
+      throw err;
+    });
+  });
+};
+
 PromisePool.prototype.query = function(sql, args) {
   const corePool = this.pool;
   const localErr = new Error();