Added hooks to support mongo-db transaction

README.md

@@ -265,6 +265,71 @@ students.find({ query, collation }).then( ... );
 For more information on MongoDB's collation feature, visit the [collation reference page](https://docs.mongodb.com/manual/reference/collation/).
 
 
+## Mongo-DB Transaction
+
+This adapter includes support to enable database transaction to rollback the persisted records for any error occured for a api call. This requires  [Mongo-DB v4.x](https://docs.mongodb.com/manual/) installed.
+
+Start working with transactin enabled by adding the following lines in `app.hooks.js`.
+
+```js
+const TransactionManager = require('feathers-mongoose').TransactionManager;
+const isTransactionEnable = process.env.TRANSACTION_ENABLE || false;
+const skipPath = ['login'];
+
+let moduleExports = {
+  before: {
+    // !<DEFAULT> code: before
+    all: [],
+    find: [],
+    get: [],
+    create: [
+      when(isTransactionEnable, async hook =>
+        TransactionManager.beginTransaction(hook, skipPath)
+      )
+    ],
+    update: [
+      when(isTransactionEnable, async hook =>
+        TransactionManager.beginTransaction(hook, skipPath)
+      )
+    ],
+    patch: [],
+    remove: []
+    // !end
+  },
+
+  after: {
+    // !<DEFAULT> code: after
+    all: [log()],
+    find: [],
+    get: [],
+    create: [when(isTransactionEnable, TransactionManager.commitTransaction)],
+    update: [when(isTransactionEnable, TransactionManager.commitTransaction)],
+    patch: [],
+    remove: [afterAudit]
+    // !end
+  },
+
+  error: {
+    // !<DEFAULT> code: error
+    all: [log()],
+    find: [],
+    get: [],
+    create: [when(isTransactionEnable, TransactionManager.rollbackTransaction)],
+    update: [when(isTransactionEnable, TransactionManager.rollbackTransaction)],
+    patch: [],
+    remove: []
+    // !end
+  }
+  // !code: moduleExports // !end
+};
+
+// !code: exports // !end
+module.exports = moduleExports;
+
+// !code: funcs // !end
+// !code: end // !end
+```
+
 ## License
 
 [MIT](LICENSE)

lib/index.js

@@ -1,6 +1,8 @@
 const hooks = require('./hooks');
 const service = require('./service');
+const transactionManager = require('./transaction-manager');
 
 Object.assign(service, { hooks, service });
 
 module.exports = service;
+module.exports.TransactionManager = transactionManager;

lib/transaction-manager.js

@@ -0,0 +1,93 @@
+const errors = require('@feathersjs/errors');
+const mongoose = require('mongoose');
+
+/**
+ * To start a new session and initiate transaction on the session and set
+ * mongoose-session in context-params to all consecutive service call if the
+ * boolean
+ *
+ * @param {object} context                            context and all params
+ * @param {[string]} skipPath      list of paths to exclude from transaction
+ *                                                     -  Example: ['login']
+ * @return {object} context                 context with db-session appended
+ */
+const beginTransaction = async (context, skipPath) => {
+  try {
+    // if the current path is not added to skipPath-list
+    if (skipPath.indexOf(context.path) === -1) {
+      // if there is no open-transaction appended already
+      if (context.params && !context.params.transactionOpen) {
+        const session = await mongoose.startSession();
+        session.startTransaction();
+        context.params.transactionOpen = true;
+        context.params.mongoose = { session };
+      }
+      context.enableTransaction = true;     // true if transaction is enabled
+    } else {
+      context.enableTransaction = false;
+    }
+    return context;
+  } catch (err) {
+    throw new errors.MongoError(`Error while starting session`);
+  }
+};
+
+/**
+ * To commit a mongo-transaction after save methods of mongo service
+ *
+ * @param {object} context           context with params, result and DB-session
+ * @return {object} context          context with params, result and DB-session
+ */
+const commitTransaction = async context => {
+  try {
+    // if transaction is enabled during startSession
+    if (context.enableTransaction)
+      // if context contains the mongoose session to be committed
+      if (
+        context.params &&
+        context.params.mongoose &&
+        context.params.mongoose.session
+      ) {
+        await context.params.mongoose.session.commitTransaction();
+        context.params.mongoose = null;
+        context.params.transactionOpen = false;       // reset transaction-open
+        context.enableTransaction = false;
+      }
+    return context;
+  } catch (err) {
+    throw new errors.MongoError(`Error while commiting transaction`);
+  }
+};
+
+/**
+ * To rollback a mongo-transaction for any error thrown in service calls
+ *
+ * @param {object} context            context with params and DB-session
+ * @return {object} context           context with params and DB-session
+ */
+const rollbackTransaction = async context => {
+  try {
+    // if transaction is enabled during startSession
+    if (context.enableTransaction)
+      // if context contains the mongoose session to be committed
+      if (
+        context.params &&
+        context.params.mongoose &&
+        context.params.mongoose.session
+      ) {
+        await context.params.mongoose.session.abortTransaction();
+        context.params.mongoose = null;
+        context.transactionOpen = false;      // reset transaction-open
+        context.enableTransaction = false;
+      }
+    return context;
+  } catch (err) {
+    throw new errors.MongoError(`Error while rolling-back transaction`);
+  }
+};
+
+module.exports = {
+  beginTransaction,
+  commitTransaction,
+  rollbackTransaction
+};