fix: respect readPreference and writeConcern from connection string

lib/operations/connect.js

@@ -308,6 +308,10 @@ function connect(mongoClient, url, options, callback) {
     // Store the merged options object
     mongoClient.s.options = _finalOptions;
 
+    // Apply read and write concern from parsed url
+    mongoClient.s.readPreference = ReadPreference.fromOptions(_finalOptions);
+    mongoClient.s.writeConcern = WriteConcern.fromOptions(_finalOptions);
+
     // Failure modes
     if (object.servers.length === 0) {
       return callback(new Error('connection string must contain at least one seed host'));

test/functional/readpreference.test.js

@@ -4,9 +4,12 @@ const Topology = require('../../lib/core/sdam/topology').Topology;
 const test = require('./shared').assert;
 const setupDatabase = require('./shared').setupDatabase;
 const withMonitoredClient = require('./shared').withMonitoredClient;
-const expect = require('chai').expect;
+
 const ReadPreference = require('../../lib/core/topologies/read_preference');
 const withClient = require('./shared').withClient;
+const chai = require('chai');
+chai.use(require('chai-subset'));
+const expect = chai.expect;
 
 describe('ReadPreference', function() {
   before(function() {
@@ -729,4 +732,31 @@ describe('ReadPreference', function() {
       });
     });
   });
+
+  it('should respect readPreference from uri', {
+    metadata: { requires: { topology: 'replicaset', mongodb: '>=3.6' } },
+    test: withMonitoredClient('find', { queryOptions: { readPreference: 'secondary' } }, function(
+      client,
+      events,
+      done
+    ) {
+      expect(client.readPreference.mode).to.equal('secondary');
+      client
+        .db('test')
+        .collection('test')
+        .findOne({ a: 1 }, err => {
+          expect(err).to.not.exist;
+          expect(events)
+            .to.be.an('array')
+            .with.lengthOf(1);
+          expect(events[0]).to.containSubset({
+            commandName: 'find',
+            command: {
+              $readPreference: { mode: 'secondary' }
+            }
+          });
+          done();
+        });
+    })
+  });
 });

test/functional/write_concern.test.js

@@ -21,6 +21,30 @@ describe('Write Concern', function() {
     generateTopologyTests(testSuites, testContext);
   });
 
+  it(
+    'should respect writeConcern from uri',
+    withMonitoredClient('insert', { queryOptions: { w: 0 } }, function(client, events, done) {
+      expect(client.writeConcern).to.eql({ w: 0 });
+      client
+        .db('test')
+        .collection('test')
+        .insertOne({ a: 1 }, (err, result) => {
+          expect(err).to.not.exist;
+          expect(result).to.exist;
+          expect(events)
+            .to.be.an('array')
+            .with.lengthOf(1);
+          expect(events[0]).to.containSubset({
+            commandName: 'insert',
+            command: {
+              writeConcern: { w: 0 }
+            }
+          });
+          done();
+        });
+    })
+  );
+
   // TODO: once `read-write-concern/connection-string` spec tests are implemented these can likely be removed
   describe('test journal connection string option', function() {
     function journalOptionTest(client, events, done) {