refactor(populate): move execPopulateQuery() calls after all querie…

…s are computed re: #3812

lib/model.js

@@ -4124,6 +4124,7 @@ function populate(model, docs, options, callback) {
 
   let _remaining = len;
   let hasOne = false;
+  const params = [];
   for (let i = 0; i < len; ++i) {
     const mod = modelsMap[i];
     let select = mod.options.select;
@@ -4189,11 +4190,7 @@ function populate(model, docs, options, callback) {
       mod.options.options.limit = mod.options.options.limit * ids.length;
     }
 
-    _execQuery(mod, match, select, (err, valsFromDb) => {
-      if (mod.options.options && mod.options.options.limit) {
-        mod.options.options.limit = assignmentOpts.originalLimit;
-      }
-
+    params.push([mod, match, select, assignmentOpts, (err, valsFromDb) => {
       if (err != null) {
         return callback(err, null);
       }
@@ -4202,15 +4199,23 @@ function populate(model, docs, options, callback) {
       if (--_remaining === 0) {
         callback();
       }
-    });
+    }]);
   }
 
   if (!hasOne) {
     return callback();
   }
+
+  for (const arr of params) {
+    _execPopulateQuery.apply(null, arr);
+  }
 }
 
-function _execQuery(mod, match, select, callback) {
+/*!
+ * ignore
+ */
+
+function _execPopulateQuery(mod, match, select, assignmentOpts, callback) {
   const subPopulate = utils.clone(mod.options.populate);
 
   const query = mod.model.find(match, select, mod.options.options);
@@ -4239,6 +4244,10 @@ function _execQuery(mod, match, select, callback) {
   }
 
   query.exec(callback);
+
+  if (mod.options.options && mod.options.options.limit) {
+    mod.options.options.limit = assignmentOpts.originalLimit;
+  }
 }
 
 /*!