Add method to get current transaction id, #267

README.md

@@ -168,6 +168,11 @@ This will run the provided callback in a transaction much like `transaction` exc
 
 The `childTransaction` function can be executed on its own (to run the child transaction inside the next queued transaction), or it can be executed inside another transaction callback, executing the child transaction within the current transaction.
 
+### `db.getWriteTxnId(): number`
+Returns the transaction id of the currently executing transaction. This is an integer that increments with each
+transaction. This is only available inside transaction callbacks (for transactionSync or asynchronous transaction),
+and does not provide access transaction ids for asynchronous put/delete methods (the `aftercommit` method can be
+used for that).
 
 ### `db.committed: Promise`
 This is a promise-like object that resolves when all previous writes have been committed.

index.d.ts

@@ -187,6 +187,13 @@ declare namespace lmdb {
 		* @param action The function to execute within the transaction
 		**/
 		childTransaction<T>(action: () => T): Promise<T>
+		/**
+		 * Returns the transaction id of the currently executing transaction. This is an integer that increments with each
+		 * transaction. This is only available inside transaction callbacks (for transactionSync or asynchronous transaction),
+		 * and does not provide access transaction ids for asynchronous put/delete methods (the 'aftercommit' method can be
+		 * used for that).
+		 */
+		getWriteTxnId(): number
 		/**
 		* Returns the current transaction and marks it as in use. This can then be explicitly used for read operations
 		* @returns The transaction object

src/env.cpp

@@ -970,6 +970,18 @@ Napi::Value EnvWrap::abortTxn(const CallbackInfo& info) {
 	delete currentTxn;
 	return info.Env().Undefined();
 }
+Napi::Value EnvWrap::getWriteTxnId(const Napi::CallbackInfo& info) {
+	TxnTracked *currentTxn = this->writeTxn;
+	size_t txn_id;
+	if (currentTxn) {
+		txn_id = mdb_txn_id(currentTxn->txn);
+	} else if (this->writeWorker) {
+		txn_id = mdb_txn_id(this->writeWorker->txn);
+	} else return throwError(info.Env(), "There is no active write transaction.");
+	return Number::New(info.Env(), txn_id);
+}
+
+
 /*Napi::Value EnvWrap::openDbi(const CallbackInfo& info) {
 
 
@@ -1171,6 +1183,7 @@ void EnvWrap::setupExports(Napi::Env env, Object exports) {
 		EnvWrap::InstanceMethod("beginTxn", &EnvWrap::beginTxn),
 		EnvWrap::InstanceMethod("commitTxn", &EnvWrap::commitTxn),
 		EnvWrap::InstanceMethod("abortTxn", &EnvWrap::abortTxn),
+		EnvWrap::InstanceMethod("getWriteTxnId", &EnvWrap::getWriteTxnId),
 		EnvWrap::InstanceMethod("sync", &EnvWrap::sync),
 		EnvWrap::InstanceMethod("resumeWriting", &EnvWrap::resumeWriting),
 		EnvWrap::InstanceMethod("startWriting", &EnvWrap::startWriting),

src/lmdb-js.h

@@ -426,6 +426,7 @@ class EnvWrap : public ObjectWrap<EnvWrap> {
 	Napi::Value beginTxn(const CallbackInfo& info);
 	Napi::Value commitTxn(const CallbackInfo& info);
 	Napi::Value abortTxn(const CallbackInfo& info);
+	Napi::Value getWriteTxnId(const CallbackInfo& info);
 
 	/*
 		Flushes all data to the disk asynchronously.

test/index.test.js

@@ -946,6 +946,7 @@ describe('lmdb-js', function () {
 					}
 					db2.put('key2-async', 'async test 2');
 					should.equal(db2.get('key2-async'), 'async test 2');
+					expect(db.getWriteTxnId()).gte(1);
 				});
 				should.equal(db.get('key1'), 'async test 1');
 				should.equal(db2.get('key2-async'), 'async test 2');
@@ -1152,9 +1153,11 @@ describe('lmdb-js', function () {
 						db.childTransaction(() => {
 							iterator = db.getRange({ start: 'c1' })[Symbol.iterator]();
 							should.equal(iterator.next().value.value, 'value1');
+							expect(db.getWriteTxnId()).gte(1);
 						});
 					}
 					should.equal(iterator.next().value.value, 'value2');
+					expect(db.getWriteTxnId()).gte(1);
 				});
 				should.equal(iterator.next().value.value, 'value3');
 			});

write.js

@@ -840,6 +840,9 @@ export function addWriteMethods(LMDBStore, { env, fixedBuffer, resetReadTxn, use
 				throw error;
 			}
 		},
+		getWriteTxnId() {
+			return env.getWriteTxnId();
+		},
 		transactionSyncStart(callback) {
 			return this.transactionSync(callback, 0);
 		},