SERVER-22043 attach read preference in count helper

(cherry picked from commit a7820c6af9c4474239f8f80c88d9de7722fa900a)

2 files changed, 41 insertions, 1 deletions

diff --git a/jstests/noPassthrough/count_helper_read_preference.js b/jstests/noPassthrough/count_helper_read_preference.js
new file mode 100644
index 00000000000..b888107ccd6
--- /dev/null
+++ b/jstests/noPassthrough/count_helper_read_preference.js
@@ -0,0 +1,40 @@
+// Tests that the read preference set on the connection is used when we call the count helper.
+(function() {
+    "use strict";
+
+    var commandsRan = [];
+
+    // Create a new DB object backed by a mock connection.
+    function MockMongo() {};
+    MockMongo.prototype = Mongo.prototype;
+    MockMongo.prototype.runCommand = function(db, cmd, opts) {
+        commandsRan.push({db: db, cmd: cmd, opts:opts});
+        return {ok: 1, n: 100};
+    };
+    var db = new DB(new MockMongo(), "test");
+
+    assert.eq(commandsRan.length, 0);
+
+    // Run a count with no readPref.
+    db.getMongo().setReadPref(null);
+    db.foo.count();
+
+    // Check that there is no readPref on the command document.
+    assert.eq(commandsRan.length, 1);
+    assert.docEq(commandsRan[0].cmd, {count: "foo", fields: {}, query: {}});
+
+    commandsRan = [];
+
+    // Run with readPref secondary.
+    db.getMongo().setReadPref("secondary");
+    db.foo.count();
+
+    // Check that we have wrapped the command and attached the read preference.
+    assert.eq(commandsRan.length, 1);
+    assert.docEq(commandsRan[0].cmd,
+                 {query: {count: "foo",
+                           fields: {},
+                           query: {}},
+                  $readPreference: {mode: "secondary"}});
+
+})();
diff --git a/src/mongo/shell/query.js b/src/mongo/shell/query.js
index 1dd6d7fff1d..f0067fe4837 100644
--- a/src/mongo/shell/query.js
+++ b/src/mongo/shell/query.js
@@ -364,7 +364,7 @@ DBQuery.prototype._convertToCountCmd = function(applySkipLimit) {
 DBQuery.prototype.count = function(applySkipLimit) {
     var cmd = this._convertToCountCmd(applySkipLimit);
 
-    var res = this._db.runCommand(cmd);
+    var res = this._db.runReadCommand(cmd);
     if (res && res.n != null)
         return res.n;
     throw _getErrorWithCode(res, "count failed: " + tojson(res));