This PR adds support for .transaction()

README.md

@@ -216,6 +216,25 @@ con.promise().query("SELECT 1")
   .then( () => con.end());
 ```
 
+### 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, isolationLevel: mysql.ISOLATION_LEVEL.READ_COMMITTED}, 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.

index.js

@@ -76,3 +76,10 @@ exports.setMaxParserCache = function(max) {
 exports.clearParserCache = function() {
   parserCache.clearCache();
 };
+
+exports.ISOLATION_LEVEL = {
+  READ_UNCOMMITTED: 'READ UNCOMMITTED',
+  READ_COMMITTED: 'READ COMMITTED',
+  REPEATABLE_READ: 'REPEATABLE READ',
+  SERIALIZABLE: 'SERIALIZABLE'
+};

lib/connection.js

@@ -638,8 +638,27 @@ class Connection extends EventEmitter {
   }
 
   // transaction helpers
-  beginTransaction(cb) {
-    return this.query('START TRANSACTION', cb);
+  beginTransaction(options,cb) {
+    if (cb === undefined) {
+     cb = options;
+     options = {};
+    }
+
+    const startTransactionSQL = 
+      "START TRANSACTION" +
+      ( options.consistentSnapshot === true ? " WITH CONSISTENT SNAPSHOT," : "" ) +
+      ( options.readWrite !== false ? " READ WRITE" : " READ ONLY" )
+    ;
+
+
+    if (options.isolationLevel) {
+      this.query("SET TRANSACTION ISOLATION LEVEL " + options.isolationLevel, err => {
+        if (err) return cb(err);
+        this.query(startTransactionSQL,cb);
+      });
+    } else {
+      this.query(startTransactionSQL,cb);
+    }
   }
 
   commit(cb) {

lib/packets/packet.js

@@ -528,8 +528,7 @@ class Packet {
             result.push({ x: x, y: y });
           }
           break;
-        case 3: // WKBPolygon
-          // eslint-disable-next-line no-case-declarations
+        case 3: { // WKBPolygon
           const numRings = byteOrder
             ? buffer.readUInt32LE(offset)
             : buffer.readUInt32BE(offset);
@@ -555,11 +554,11 @@ class Packet {
             result.push(line);
           }
           break;
+        }
         case 4: // WKBMultiPoint
         case 5: // WKBMultiLineString
         case 6: // WKBMultiPolygon
-        case 7: // WKBGeometryCollection
-          // eslint-disable-next-line no-case-declarations
+        case 7: { // WKBGeometryCollection
           const num = byteOrder
             ? buffer.readUInt32LE(offset)
             : buffer.readUInt32BE(offset);
@@ -569,6 +568,7 @@ class Packet {
             result.push(parseGeometry());
           }
           break;
+        }
       }
       return result;
     }

promise.js

@@ -119,15 +119,47 @@ class PromiseConnection extends EventEmitter {
     });
   }
 
-  beginTransaction() {
+  beginTransaction(options) {
     const c = this.connection;
     const localErr = new Error();
     return new this.Promise((resolve, reject) => {
       const done = makeDoneCb(resolve, reject, localErr);
-      c.beginTransaction(done);
+      c.beginTransaction(options,done);
     });
   }
 
+  transaction(options,promiseCallback) {
+    if (! promiseCallback) {
+      promiseCallback = options;
+      options = {};
+    }
+    options = options || {};
+
+    let promiseChain = this.Promise.resolve();
+
+    if (options.autoCommit !== true) {
+      promiseChain = promiseChain.then(() => this.beginTransaction(options));
+    }
+
+    promiseChain = promiseChain.then(() => promiseCallback(this));
+
+    if (options.autoCommit !== true) {
+      promiseChain = promiseChain
+      .then( res => 
+        this.commit()
+        .then(
+          () => res
+        )
+      )
+      .catch( err => 
+        this.rollback()
+        .catch(() => null)
+        .then(() => { throw err })
+      )
+    }
+    return promiseChain;
+  }
+
   commit() {
     const c = this.connection;
     const localErr = new Error();
@@ -330,6 +362,21 @@ class PromisePool extends EventEmitter {
     });
   }
 
+  transaction(options,promiseCallback) {
+    return this.getConnection()
+    .then(con => 
+      con.transaction(options,promiseCallback)
+      .then(res => {
+        con.release();
+        return res;
+      })
+      .catch(err => {
+        con.release();
+        throw err;
+      })
+    );
+  }
+
   execute(sql, values) {
     const corePool = this.pool;
     const localErr = new Error();
@@ -403,3 +450,4 @@ exports.raw = core.raw;
 exports.PromisePool = PromisePool;
 exports.PromiseConnection = PromiseConnection;
 exports.PromisePoolConnection = PromisePoolConnection;
+exports.ISOLATION_LEVEL = core.ISOLATION_LEVEL;