fix: db.command to not inherit options from parent

Fixes `db.command` method to not inherit readPreference, writeConcern, readConcern
from parent. centralizes readPreference helpers translate, resolve, fromOptions to the
ReadPreference class. Adds Aspect "NO_INHERIT_OPTIONS" to command operations
for flagging specific operations. Creates `RunCommand` operation to wrap
`CommandV2`, updating `db.command` to use `CommandV2`.

NODE-2649

src/db.ts

@@ -26,6 +26,7 @@ import AggregateOperation = require('./operations/aggregate');
 import AddUserOperation = require('./operations/add_user');
 import CollectionsOperation = require('./operations/collections');
 import CommandOperation = require('./operations/command');
+import RunCommandOperation = require('./operations/run_command');
 import CreateCollectionOperation = require('./operations/create_collection');
 import CreateIndexesOperation = require('./operations/create_indexes');
 import { DropCollectionOperation, DropDatabaseOperation } from './operations/drop';
@@ -241,7 +242,7 @@ class Db {
     if (typeof options === 'function') (callback = options), (options = {});
     options = Object.assign({}, options);
 
-    const commandOperation = new CommandOperation(this, options, null, command);
+    const commandOperation = new RunCommandOperation(this, command, options);
 
     return executeOperation(this.s.topology, commandOperation, callback);
   }

src/operations/command_v2.ts

@@ -27,9 +27,10 @@ class CommandOperationV2 extends OperationBase {
     super(options);
 
     this.ns = parent.s.namespace.withCollection('$cmd');
-    this.readPreference = ReadPreference.resolve(parent, this.options);
-    this.readConcern = resolveReadConcern(parent, this.options);
-    this.writeConcern = resolveWriteConcern(parent, this.options);
+    const propertyProvider = this.hasAspect(Aspect.NO_INHERIT_OPTIONS) ? undefined : parent;
+    this.readPreference = ReadPreference.resolve(propertyProvider, this.options);
+    this.readConcern = resolveReadConcern(propertyProvider, this.options);
+    this.writeConcern = resolveWriteConcern(propertyProvider, this.options);
     this.explain = false;
 
     if (operationOptions && typeof operationOptions.fullResponse === 'boolean') {
@@ -108,11 +109,11 @@ class CommandOperationV2 extends OperationBase {
 }
 
 function resolveWriteConcern(parent: any, options: any) {
-  return WriteConcern.fromOptions(options) || parent.writeConcern;
+  return WriteConcern.fromOptions(options) || (parent && parent.writeConcern);
 }
 
 function resolveReadConcern(parent: any, options: any) {
-  return ReadConcern.fromOptions(options) || parent.readConcern;
+  return ReadConcern.fromOptions(options) || (parent && parent.readConcern);
 }
 
 export = CommandOperationV2;

src/operations/operation.ts

@@ -2,7 +2,8 @@ const Aspect = {
   READ_OPERATION: Symbol('READ_OPERATION'),
   WRITE_OPERATION: Symbol('WRITE_OPERATION'),
   RETRYABLE: Symbol('RETRYABLE'),
-  EXECUTE_WITH_SELECTION: Symbol('EXECUTE_WITH_SELECTION')
+  EXECUTE_WITH_SELECTION: Symbol('EXECUTE_WITH_SELECTION'),
+  NO_INHERIT_OPTIONS: Symbol('NO_INHERIT_OPTIONS')
 };
 
 /**

src/operations/run_command.ts

@@ -0,0 +1,21 @@
+import CommandOperationV2 = require('./command_v2');
+import { defineAspects, Aspect } from './operation';
+import Db = require('../db');
+import Collection = require('../collection');
+import MongoClient = require('../mongo_client');
+import { Server } from '../sdam/server';
+
+class RunCommandOperation extends CommandOperationV2 {
+  command: any;
+  constructor(parent: MongoClient | Db | Collection, command: any, options: any) {
+    super(parent, options);
+    this.command = command;
+  }
+  execute(server: Server, callback: any) {
+    const command = this.command;
+    this.executeCommand(server, command, callback);
+  }
+}
+defineAspects(RunCommandOperation, [Aspect.EXECUTE_WITH_SELECTION, Aspect.NO_INHERIT_OPTIONS]);
+
+export = RunCommandOperation;

src/read_preference.ts

@@ -127,7 +127,7 @@ class ReadPreference {
     options = options || {};
     const session = options.session;
 
-    const inheritedReadPreference = parent.readPreference;
+    const inheritedReadPreference = parent && parent.readPreference;
 
     let readPreference;
     if (options.readPreference) {
@@ -138,7 +138,7 @@ class ReadPreference {
     } else if (inheritedReadPreference != null) {
       readPreference = inheritedReadPreference;
     } else {
-      throw new Error('No readPreference was provided or inherited.');
+      readPreference = ReadPreference.primary;
     }
 
     return typeof readPreference === 'string' ? new ReadPreference(readPreference) : readPreference;
@@ -148,12 +148,22 @@ class ReadPreference {
    * Replaces options.readPreference with a ReadPreference instance
    */
   static translate(options: any) {
-    if (options.readPreference == null) return undefined;
+    if (options.readPreference == null) return options;
     const r = options.readPreference;
-    options.readPreference = ReadPreference.fromOptions(options);
-    if (!(options.readPreference instanceof ReadPreference)) {
+
+    if (typeof r === 'string') {
+      options.readPreference = new ReadPreference(r);
+    } else if (r && !(r instanceof ReadPreference) && typeof r === 'object') {
+      const mode = r.mode || r.preference;
+      if (mode && typeof mode === 'string') {
+        options.readPreference = new ReadPreference(mode, r.tags, {
+          maxStalenessSeconds: r.maxStalenessSeconds
+        });
+      }
+    } else if (!(r instanceof ReadPreference)) {
       throw new TypeError('Invalid read preference: ' + r);
     }
+
     return options;
   }