Started with database connection

app/node_modules/mysql2/lib/pool_connection.js

@@ -0,0 +1,69 @@
+'use strict';
+
+const Connection = require('../index.js').Connection;
+
+class PoolConnection extends Connection {
+  constructor(pool, options) {
+    super(options);
+    this._pool = pool;
+    // The last active time of this connection
+    this.lastActiveTime = Date.now();
+    // When a fatal error occurs the connection's protocol ends, which will cause
+    // the connection to end as well, thus we only need to watch for the end event
+    // and we will be notified of disconnects.
+    // REVIEW: Moved to `once`
+    this.once('end', () => {
+      this._removeFromPool();
+    });
+    this.once('error', () => {
+      this._removeFromPool();
+    });
+  }
+
+  release() {
+    if (!this._pool || this._pool._closed) {
+      return;
+    }
+    // update last active time
+    this.lastActiveTime = Date.now();
+    this._pool.releaseConnection(this);
+  }
+
+  promise(promiseImpl) {
+    const PromisePoolConnection = require('../promise').PromisePoolConnection;
+    return new PromisePoolConnection(this, promiseImpl);
+  }
+
+  end() {
+    const err = new Error(
+      'Calling conn.end() to release a pooled connection is ' +
+        'deprecated. In next version calling conn.end() will be ' +
+        'restored to default conn.end() behavior. Use ' +
+        'conn.release() instead.'
+    );
+    this.emit('warn', err);
+    // eslint-disable-next-line no-console
+    console.warn(err.message);
+    this.release();
+  }
+
+  destroy() {
+    this._removeFromPool();
+    super.destroy();
+  }
+
+  _removeFromPool() {
+    if (!this._pool || this._pool._closed) {
+      return;
+    }
+    const pool = this._pool;
+    this._pool = null;
+    pool._removeConnection(this);
+  }
+}
+
+PoolConnection.statementKey = Connection.statementKey;
+module.exports = PoolConnection;
+
+// TODO: Remove this when we are removing PoolConnection#end
+PoolConnection.prototype._realEnd = Connection.prototype.end;