SERVER-18557 remove usage of $cmd.findOne from shell and jstests

jstests/core/count5.js

@@ -26,5 +26,5 @@ assert.eq( 2 , t.find( q ).skip(48).limit(5).size() , "I" );
 assert.eq( 20 , t.find().limit(20).size() , "J" );
 
 assert.eq( 0 , t.find().skip(120).size() , "K" );
-assert.eq( 1 , db.$cmd.findOne( { count: "count5" } )["ok"] , "L" );
-assert.eq( 1 , db.$cmd.findOne( { count: "count5", skip: 120 } )["ok"] , "M" );
+assert.eq( 1 , db.runCommand( { count: "count5" } )["ok"] , "L" );
+assert.eq( 1 , db.runCommand( { count: "count5", skip: 120 } )["ok"] , "M" );

jstests/gle/core/error1.js

@@ -1,9 +1,9 @@
 db.jstests_error1.drop();
 
 // test 1
-db.$cmd.findOne({reseterror:1});
-assert( db.$cmd.findOne({getlasterror:1}).err == null, "A" );
-assert( db.$cmd.findOne({getpreverror:1}).err == null, "B" );
+db.runCommand({reseterror:1});
+assert( db.runCommand({getlasterror:1}).err == null, "A" );
+assert( db.runCommand({getpreverror:1}).err == null, "B" );
 
 db.resetError();
 assert( db.getLastError() == null, "C" );
@@ -11,9 +11,9 @@ assert( db.getPrevError().err == null , "preverror 1" );
 
 // test 2
 
-db.$cmd.findOne({forceerror:1});
-assert( db.$cmd.findOne({getlasterror:1}).err != null, "D" );
-assert( db.$cmd.findOne({getpreverror:1}).err != null, "E" );
+db.runCommand({forceerror:1});
+assert( db.runCommand({getlasterror:1}).err != null, "D" );
+assert( db.runCommand({getpreverror:1}).err != null, "E" );
 
 
 assert( db.getLastError() != null, "F" );
@@ -21,14 +21,14 @@ assert( db.getPrevError().err != null , "preverror 2" );
 assert( db.getPrevError().nPrev == 1, "G" );
 
 db.jstests_error1.findOne();
-assert( db.$cmd.findOne({getlasterror:1}).err == null, "H" );
-assert( db.$cmd.findOne({getpreverror:1}).err != null, "I" );
-assert( db.$cmd.findOne({getpreverror:1}).nPrev == 2, "J" );
+assert( db.runCommand({getlasterror:1}).err == null, "H" );
+assert( db.runCommand({getpreverror:1}).err != null, "I" );
+assert( db.runCommand({getpreverror:1}).nPrev == 2, "J" );
 
 db.jstests_error1.findOne();
-assert( db.$cmd.findOne({getlasterror:1}).err == null, "K" );
-assert( db.$cmd.findOne({getpreverror:1}).err != null, "L" );
-assert( db.$cmd.findOne({getpreverror:1}).nPrev == 3, "M" );
+assert( db.runCommand({getlasterror:1}).err == null, "K" );
+assert( db.runCommand({getpreverror:1}).err != null, "L" );
+assert( db.runCommand({getpreverror:1}).nPrev == 3, "M" );
 
 db.resetError();
 db.forceError();
@@ -37,5 +37,5 @@ assert( db.getLastError() == null , "getLastError 5" );
 assert( db.getPrevError().err != null , "preverror 3" );
 
 // test 3
-db.$cmd.findOne({reseterror:1});
-assert( db.$cmd.findOne({getpreverror:1}).err == null, "N" );
+db.runCommand({reseterror:1});
+assert( db.runCommand({getpreverror:1}).err == null, "N" );

src/mongo/shell/db.js

@@ -45,11 +45,10 @@ DB.prototype.commandHelp = function( name ){
 }
 
  // utility to attach readPreference if needed.
- DB.prototype._attachReadPreferenceToCommand = function (cmdObj) {
+ DB.prototype._attachReadPreferenceToCommand = function (cmdObj, readPref) {
      "use strict";
-     var readPref = this.getMongo().getReadPref();
      // if the user has not set a readpref, return the original cmdObj
-     if (readPref === null) {
+     if ((readPref === null) || typeof(readPref) !== "object") {
          return cmdObj;
      }
 
@@ -86,21 +85,24 @@ DB.prototype.commandHelp = function( name ){
  };
 
  // Like runCommand but applies readPreference if one has been set
- // on the connection. Also sets options automatically.
+ // on the connection. Also sets slaveOk if a (non-primary) readPref has been set.
  DB.prototype.runReadCommand = function (obj, extra) {
      "use strict";
 
+     // Support users who call this function with a string commandName, e.g.
+     // db.runReadCommand("commandName", {arg1: "value", arg2: "value"}).
      var mergedObj = (typeof(obj) === "string") ? this._mergeCommandOptions(obj, extra) : obj;
-     var cmdObjWithReadPref = this._attachReadPreferenceToCommand(obj);
+     var cmdObjWithReadPref =
+         this._attachReadPreferenceToCommand(mergedObj,
+                                             this.getMongo().getReadPref());
 
      var options = 0;
-     // automatically set slaveOk if readPreference is anything but primary
+     // We automatically set slaveOk if readPreference is anything but primary.
      if (this.getMongo().getReadPrefMode() !== "primary") {
          options |= 4;
      }
 
-     // allow options to be overridden
-     // extra is not used since mergedObj is an object
+     // The 'extra' parameter is not used as we have already created a merged command object.
      return this.runCommand(cmdObjWithReadPref, null, options);
  };
 

src/mongo/shell/explain_query.js

@@ -160,25 +160,15 @@ var DBExplainQuery = (function() {
                 var explainCmd = {explain: innerCmd};
                 explainCmd["verbosity"] = this._verbosity;
 
-                // We explicitly run a find against the $cmd collection instead of using the
-                // runCommand helper so that we can set a read preference on the command.
-                var cmdColl = this._query._db.getCollection("$cmd");
-                var cmdQuery = cmdColl.find(explainCmd,
-                                            {}, // projection
-                                            -1, // limit
-                                            0, // skip
-                                            0, // batchSize
-                                            this._query._options);
+                var explainDb = this._query._db;
 
-                // Handle read preference.
                 if ("$readPreference" in this._query._query) {
-                    // A read preference was set on the query. Pull the read pref up so that it is
-                    // set on the explain command.
                     var prefObj = this._query._query.$readPreference;
-                    cmdQuery.readPref(prefObj.mode, prefObj.tags);
+                    explainCmd = explainDb._attachReadPreferenceToCommand(explainCmd, prefObj);
                 }
 
-                var explainResult = cmdQuery.next();
+                var explainResult = explainDb.runCommand(explainCmd, null, this._query._options);
+
                 if (!explainResult.ok && explainResult.code === CMD_NOT_FOUND_CODE) {
                     // One of the shards doesn't have the explain command available. Retry using
                     // the legacy $explain format, which should be supported by all shards.