diff --git a/lib/sequence.js b/lib/sequence.js
index d222194..11bdf73 100644
--- a/lib/sequence.js
+++ b/lib/sequence.js
@@ -110,13 +110,14 @@ Sequence.prototype.getId = function() {
  *                       reference
  */
 Sequence.prototype._getCounterReferenceField = function(doc) {
-    var reference = [];
+    var reference = {};
 
     if (this._useReference === false) {
         reference = null;
     }else {
         for (var i in this._options.reference_fields) {
-            reference.push(JSON.stringify(doc[this._options.reference_fields[i]]));
+            reference[this._options.reference_fields[i]] = doc[this._options.reference_fields[i]];
+            // reference.push(JSON.stringify(doc[this._options.reference_fields[i]]));
         }
     }
 
@@ -153,7 +154,7 @@ Sequence.prototype._createCounterModel = function() {
     CounterSchema = mongoose.Schema(
         {
             id: {type: String, required: true},
-            reference_value: {type:Array, required: true},
+            reference_value: { type: mongoose.Schema.Types.Mixed, required: true},
             seq: {type:Number, default: 0, required: true}
         },
         {
diff --git a/package-lock.json b/package-lock.json
index 271403f..43bd115 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "mongoose-sequence",
-  "version": "4.0.0",
+  "version": "4.0.1",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
@@ -22,7 +22,7 @@
       "integrity": "sha1-r9+UiPsezvyDSPb7IvRk4ypYs2s=",
       "dev": true,
       "requires": {
-        "acorn": "3.3.0"
+        "acorn": "^3.0.4"
       },
       "dependencies": {
         "acorn": {
@@ -39,8 +39,8 @@
       "integrity": "sha1-gv+wKynmYq5TvcIK8VlHcGc5xTY=",
       "dev": true,
       "requires": {
-        "co": "4.6.0",
-        "json-stable-stringify": "1.0.1"
+        "co": "^4.6.0",
+        "json-stable-stringify": "^1.0.1"
       }
     },
     "ajv-keywords": {
@@ -55,9 +55,9 @@
       "integrity": "sha1-DNkKVhCT810KmSVsIrcGlDP60Rc=",
       "dev": true,
       "requires": {
-        "kind-of": "3.2.2",
-        "longest": "1.0.1",
-        "repeat-string": "1.6.1"
+        "kind-of": "^3.0.2",
+        "longest": "^1.0.1",
+        "repeat-string": "^1.5.2"
       }
     },
     "amdefine": {
@@ -90,7 +90,7 @@
       "integrity": "sha1-c9g7wmP4bpf4zE9rrhsOkKfSLIY=",
       "dev": true,
       "requires": {
-        "sprintf-js": "1.0.3"
+        "sprintf-js": "~1.0.2"
       }
     },
     "array-differ": {
@@ -105,7 +105,7 @@
       "integrity": "sha1-mjRBDk9OPaI96jdb5b5w8kd47Dk=",
       "dev": true,
       "requires": {
-        "array-uniq": "1.0.3"
+        "array-uniq": "^1.0.1"
       }
     },
     "array-uniq": {
@@ -143,7 +143,7 @@
       "resolved": "https://registry.npmjs.org/async/-/async-2.5.0.tgz",
       "integrity": "sha512-e+lJAJeNWuPCNyxZKOBdaJGyLGHugXVQtrAwtuAe2vhxTYxFTKE73p8JuTmdH0qdQZtDvI4dhJwjZc5zsfIsYw==",
       "requires": {
-        "lodash": "4.17.4"
+        "lodash": "^4.14.0"
       }
     },
     "asynckit": {
@@ -177,7 +177,7 @@
       "dev": true,
       "optional": true,
       "requires": {
-        "tweetnacl": "0.14.5"
+        "tweetnacl": "^0.14.3"
       }
     },
     "bluebird": {
@@ -192,7 +192,7 @@
       "integrity": "sha1-OciRjO/1eZ+D+UkqhI9iWt0Mdm8=",
       "dev": true,
       "requires": {
-        "hoek": "2.16.3"
+        "hoek": "2.x.x"
       }
     },
     "brace-expansion": {
@@ -201,7 +201,7 @@
       "integrity": "sha1-wHshHHyVLsH479Uad+8NHTmQopI=",
       "dev": true,
       "requires": {
-        "balanced-match": "1.0.0",
+        "balanced-match": "^1.0.0",
         "concat-map": "0.0.1"
       }
     },
@@ -223,7 +223,7 @@
       "integrity": "sha1-lAhe9jWB7NPaqSREqP6U6CV3dR8=",
       "dev": true,
       "requires": {
-        "callsites": "0.2.0"
+        "callsites": "^0.2.0"
       }
     },
     "callsites": {
@@ -252,8 +252,8 @@
       "dev": true,
       "optional": true,
       "requires": {
-        "align-text": "0.1.4",
-        "lazy-cache": "1.0.4"
+        "align-text": "^0.1.3",
+        "lazy-cache": "^1.0.3"
       }
     },
     "chai": {
@@ -262,9 +262,9 @@
       "integrity": "sha1-TQJjewZ/6Vi9v906QOxW/vc3Mkc=",
       "dev": true,
       "requires": {
-        "assertion-error": "1.0.2",
-        "deep-eql": "0.1.3",
-        "type-detect": "1.0.0"
+        "assertion-error": "^1.0.1",
+        "deep-eql": "^0.1.3",
+        "type-detect": "^1.0.0"
       }
     },
     "chalk": {
@@ -273,11 +273,11 @@
       "integrity": "sha1-qBFcVeSnAv5NFQq9OHKCKn4J/Jg=",
       "dev": true,
       "requires": {
-        "ansi-styles": "2.2.1",
-        "escape-string-regexp": "1.0.5",
-        "has-ansi": "2.0.0",
-        "strip-ansi": "3.0.1",
-        "supports-color": "2.0.0"
+        "ansi-styles": "^2.2.1",
+        "escape-string-regexp": "^1.0.2",
+        "has-ansi": "^2.0.0",
+        "strip-ansi": "^3.0.0",
+        "supports-color": "^2.0.0"
       }
     },
     "circular-json": {
@@ -292,7 +292,7 @@
       "integrity": "sha1-ZNo/fValRBLll5S9Ytw1KV6PKYc=",
       "dev": true,
       "requires": {
-        "restore-cursor": "1.0.1"
+        "restore-cursor": "^1.0.1"
       }
     },
     "cli-width": {
@@ -308,8 +308,8 @@
       "dev": true,
       "optional": true,
       "requires": {
-        "center-align": "0.1.3",
-        "right-align": "0.1.3",
+        "center-align": "^0.1.1",
+        "right-align": "^0.1.1",
         "wordwrap": "0.0.2"
       },
       "dependencies": {
@@ -352,7 +352,7 @@
       "integrity": "sha1-k4NwpXtKUd6ix3wV1cX9+JUWQAk=",
       "dev": true,
       "requires": {
-        "delayed-stream": "1.0.0"
+        "delayed-stream": "~1.0.0"
       }
     },
     "commander": {
@@ -373,9 +373,9 @@
       "integrity": "sha1-CqxmL9Ur54lk1VMvaUeE5wEQrPc=",
       "dev": true,
       "requires": {
-        "inherits": "2.0.3",
-        "readable-stream": "2.3.3",
-        "typedarray": "0.0.6"
+        "inherits": "^2.0.3",
+        "readable-stream": "^2.2.2",
+        "typedarray": "^0.0.6"
       }
     },
     "core-util-is": {
@@ -403,7 +403,7 @@
       "integrity": "sha1-O9/s3GCBR8HGcgL6KR59ylnqo7g=",
       "dev": true,
       "requires": {
-        "boom": "2.10.1"
+        "boom": "2.x.x"
       }
     },
     "d": {
@@ -412,7 +412,7 @@
       "integrity": "sha1-dUu1v+VUUdpppYuU1F9MWwRi1Y8=",
       "dev": true,
       "requires": {
-        "es5-ext": "0.10.26"
+        "es5-ext": "^0.10.9"
       }
     },
     "dashdash": {
@@ -421,7 +421,7 @@
       "integrity": "sha1-hTz6D3y+L+1d4gMmuN1YEDX24vA=",
       "dev": true,
       "requires": {
-        "assert-plus": "1.0.0"
+        "assert-plus": "^1.0.0"
       },
       "dependencies": {
         "assert-plus": {
@@ -483,13 +483,13 @@
       "integrity": "sha1-wSyYHQZ4RshLyvhiz/kw2Qf/0ag=",
       "dev": true,
       "requires": {
-        "globby": "5.0.0",
-        "is-path-cwd": "1.0.0",
-        "is-path-in-cwd": "1.0.0",
-        "object-assign": "4.1.1",
-        "pify": "2.3.0",
-        "pinkie-promise": "2.0.1",
-        "rimraf": "2.2.8"
+        "globby": "^5.0.0",
+        "is-path-cwd": "^1.0.0",
+        "is-path-in-cwd": "^1.0.0",
+        "object-assign": "^4.0.1",
+        "pify": "^2.0.0",
+        "pinkie-promise": "^2.0.0",
+        "rimraf": "^2.2.8"
       }
     },
     "delayed-stream": {
@@ -510,8 +510,8 @@
       "integrity": "sha1-N53Ocw9hZvds76TmcHoVmwLFpvo=",
       "dev": true,
       "requires": {
-        "esutils": "2.0.2",
-        "isarray": "1.0.0"
+        "esutils": "^2.0.2",
+        "isarray": "^1.0.0"
       }
     },
     "ecc-jsbn": {
@@ -521,7 +521,7 @@
       "dev": true,
       "optional": true,
       "requires": {
-        "jsbn": "0.1.1"
+        "jsbn": "~0.1.0"
       }
     },
     "es5-ext": {
@@ -530,8 +530,8 @@
       "integrity": "sha1-UbISilMbcMT2dkCTpzy+u4IYY3I=",
       "dev": true,
       "requires": {
-        "es6-iterator": "2.0.1",
-        "es6-symbol": "3.1.1"
+        "es6-iterator": "2",
+        "es6-symbol": "~3.1"
       }
     },
     "es6-iterator": {
@@ -540,9 +540,9 @@
       "integrity": "sha1-jjGcnwRTv1ddN0lAplWSDlnKVRI=",
       "dev": true,
       "requires": {
-        "d": "1.0.0",
-        "es5-ext": "0.10.26",
-        "es6-symbol": "3.1.1"
+        "d": "1",
+        "es5-ext": "^0.10.14",
+        "es6-symbol": "^3.1"
       }
     },
     "es6-map": {
@@ -551,12 +551,12 @@
       "integrity": "sha1-kTbgUD3MBqMBaQ8LsU/042TpSfA=",
       "dev": true,
       "requires": {
-        "d": "1.0.0",
-        "es5-ext": "0.10.26",
-        "es6-iterator": "2.0.1",
-        "es6-set": "0.1.5",
-        "es6-symbol": "3.1.1",
-        "event-emitter": "0.3.5"
+        "d": "1",
+        "es5-ext": "~0.10.14",
+        "es6-iterator": "~2.0.1",
+        "es6-set": "~0.1.5",
+        "es6-symbol": "~3.1.1",
+        "event-emitter": "~0.3.5"
       }
     },
     "es6-promise": {
@@ -571,11 +571,11 @@
       "integrity": "sha1-0rPsXU2ADO2BjbU40ol02wpzzLE=",
       "dev": true,
       "requires": {
-        "d": "1.0.0",
-        "es5-ext": "0.10.26",
-        "es6-iterator": "2.0.1",
+        "d": "1",
+        "es5-ext": "~0.10.14",
+        "es6-iterator": "~2.0.1",
         "es6-symbol": "3.1.1",
-        "event-emitter": "0.3.5"
+        "event-emitter": "~0.3.5"
       }
     },
     "es6-symbol": {
@@ -584,8 +584,8 @@
       "integrity": "sha1-vwDvT9q2uhtG7Le2KbTH7VcVzHc=",
       "dev": true,
       "requires": {
-        "d": "1.0.0",
-        "es5-ext": "0.10.26"
+        "d": "1",
+        "es5-ext": "~0.10.14"
       }
     },
     "es6-weak-map": {
@@ -594,10 +594,10 @@
       "integrity": "sha1-XjqzIlH/0VOKH45f+hNXdy+S2W8=",
       "dev": true,
       "requires": {
-        "d": "1.0.0",
-        "es5-ext": "0.10.26",
-        "es6-iterator": "2.0.1",
-        "es6-symbol": "3.1.1"
+        "d": "1",
+        "es5-ext": "^0.10.14",
+        "es6-iterator": "^2.0.1",
+        "es6-symbol": "^3.1.1"
       }
     },
     "escape-string-regexp": {
@@ -612,11 +612,11 @@
       "integrity": "sha1-WltTr0aTEQvrsIZ6o0MN07cKEBg=",
       "dev": true,
       "requires": {
-        "esprima": "2.7.3",
-        "estraverse": "1.9.3",
-        "esutils": "2.0.2",
-        "optionator": "0.8.2",
-        "source-map": "0.2.0"
+        "esprima": "^2.7.1",
+        "estraverse": "^1.9.1",
+        "esutils": "^2.0.2",
+        "optionator": "^0.8.1",
+        "source-map": "~0.2.0"
       },
       "dependencies": {
         "estraverse": {
@@ -633,10 +633,10 @@
       "integrity": "sha1-4Bl16BJ4GhY6ba392AOY3GTIicM=",
       "dev": true,
       "requires": {
-        "es6-map": "0.1.5",
-        "es6-weak-map": "2.0.2",
-        "esrecurse": "4.2.0",
-        "estraverse": "4.2.0"
+        "es6-map": "^0.1.3",
+        "es6-weak-map": "^2.0.1",
+        "esrecurse": "^4.1.0",
+        "estraverse": "^4.1.1"
       }
     },
     "eslint": {
@@ -645,39 +645,39 @@
       "integrity": "sha1-5MyPoPAJ+4KaquI4VaKTYL4fbBE=",
       "dev": true,
       "requires": {
-        "chalk": "1.1.3",
-        "concat-stream": "1.6.0",
-        "debug": "2.6.8",
-        "doctrine": "1.5.0",
-        "es6-map": "0.1.5",
-        "escope": "3.6.0",
-        "espree": "3.4.3",
-        "estraverse": "4.2.0",
-        "esutils": "2.0.2",
-        "file-entry-cache": "1.3.1",
-        "glob": "7.1.2",
-        "globals": "9.18.0",
-        "ignore": "3.3.3",
-        "imurmurhash": "0.1.4",
-        "inquirer": "0.12.0",
-        "is-my-json-valid": "2.16.0",
-        "is-resolvable": "1.0.0",
-        "js-yaml": "3.6.1",
-        "json-stable-stringify": "1.0.1",
-        "levn": "0.3.0",
-        "lodash": "4.17.4",
-        "mkdirp": "0.5.1",
-        "optionator": "0.8.2",
-        "path-is-absolute": "1.0.1",
-        "path-is-inside": "1.0.2",
-        "pluralize": "1.2.1",
-        "progress": "1.1.8",
-        "require-uncached": "1.0.3",
-        "shelljs": "0.6.1",
-        "strip-json-comments": "1.0.4",
-        "table": "3.8.3",
-        "text-table": "0.2.0",
-        "user-home": "2.0.0"
+        "chalk": "^1.1.3",
+        "concat-stream": "^1.4.6",
+        "debug": "^2.1.1",
+        "doctrine": "^1.2.2",
+        "es6-map": "^0.1.3",
+        "escope": "^3.6.0",
+        "espree": "^3.1.6",
+        "estraverse": "^4.2.0",
+        "esutils": "^2.0.2",
+        "file-entry-cache": "^1.1.1",
+        "glob": "^7.0.3",
+        "globals": "^9.2.0",
+        "ignore": "^3.1.2",
+        "imurmurhash": "^0.1.4",
+        "inquirer": "^0.12.0",
+        "is-my-json-valid": "^2.10.0",
+        "is-resolvable": "^1.0.0",
+        "js-yaml": "^3.5.1",
+        "json-stable-stringify": "^1.0.0",
+        "levn": "^0.3.0",
+        "lodash": "^4.0.0",
+        "mkdirp": "^0.5.0",
+        "optionator": "^0.8.1",
+        "path-is-absolute": "^1.0.0",
+        "path-is-inside": "^1.0.1",
+        "pluralize": "^1.2.1",
+        "progress": "^1.1.8",
+        "require-uncached": "^1.0.2",
+        "shelljs": "^0.6.0",
+        "strip-json-comments": "~1.0.1",
+        "table": "^3.7.8",
+        "text-table": "~0.2.0",
+        "user-home": "^2.0.0"
       },
       "dependencies": {
         "glob": {
@@ -686,12 +686,12 @@
           "integrity": "sha512-MJTUg1kjuLeQCJ+ccE4Vpa6kKVXkPYJ2mOCQyUuKLcLQsdrMCpBPUi8qVE6+YuaJkozeA9NusTAw3hLr8Xe5EQ==",
           "dev": true,
           "requires": {
-            "fs.realpath": "1.0.0",
-            "inflight": "1.0.6",
-            "inherits": "2.0.3",
-            "minimatch": "3.0.4",
-            "once": "1.4.0",
-            "path-is-absolute": "1.0.1"
+            "fs.realpath": "^1.0.0",
+            "inflight": "^1.0.4",
+            "inherits": "2",
+            "minimatch": "^3.0.4",
+            "once": "^1.3.0",
+            "path-is-absolute": "^1.0.0"
           }
         },
         "minimatch": {
@@ -700,7 +700,7 @@
           "integrity": "sha512-yJHVQEhyqPLUTgt9B83PXu6W3rx4MvvHvSUvToogpwoGDOUQ+yDrR0HRot+yOCdCO7u4hX3pWft6kWBBcqh0UA==",
           "dev": true,
           "requires": {
-            "brace-expansion": "1.1.8"
+            "brace-expansion": "^1.1.7"
           }
         }
       }
@@ -711,8 +711,8 @@
       "integrity": "sha1-KRC1zNSc6JPC//+qtP2LOjG4I3Q=",
       "dev": true,
       "requires": {
-        "acorn": "5.1.1",
-        "acorn-jsx": "3.0.1"
+        "acorn": "^5.0.1",
+        "acorn-jsx": "^3.0.0"
       }
     },
     "esprima": {
@@ -727,8 +727,8 @@
       "integrity": "sha1-+pVo2Y04I/mkHZHpAtyrnqblsWM=",
       "dev": true,
       "requires": {
-        "estraverse": "4.2.0",
-        "object-assign": "4.1.1"
+        "estraverse": "^4.1.0",
+        "object-assign": "^4.0.1"
       }
     },
     "estraverse": {
@@ -749,8 +749,8 @@
       "integrity": "sha1-34xp7vFkeSPHFXuc6DhAYQsCzDk=",
       "dev": true,
       "requires": {
-        "d": "1.0.0",
-        "es5-ext": "0.10.26"
+        "d": "1",
+        "es5-ext": "~0.10.14"
       }
     },
     "eventemitter2": {
@@ -795,8 +795,8 @@
       "integrity": "sha1-y+Hjr/zxzUS4DK3+0o3Hk6lwHS4=",
       "dev": true,
       "requires": {
-        "escape-string-regexp": "1.0.5",
-        "object-assign": "4.1.1"
+        "escape-string-regexp": "^1.0.5",
+        "object-assign": "^4.1.0"
       }
     },
     "file-entry-cache": {
@@ -805,8 +805,8 @@
       "integrity": "sha1-RMYepgeuS+nBQC9B9EJwy/4zT/g=",
       "dev": true,
       "requires": {
-        "flat-cache": "1.2.2",
-        "object-assign": "4.1.1"
+        "flat-cache": "^1.2.1",
+        "object-assign": "^4.0.1"
       }
     },
     "find-up": {
@@ -815,8 +815,8 @@
       "integrity": "sha1-ay6YIrGizgpgq2TWEOzK1TyyTQ8=",
       "dev": true,
       "requires": {
-        "path-exists": "2.1.0",
-        "pinkie-promise": "2.0.1"
+        "path-exists": "^2.0.0",
+        "pinkie-promise": "^2.0.0"
       }
     },
     "findup-sync": {
@@ -825,8 +825,8 @@
       "integrity": "sha1-fz56l7gjksZTvwZYm9hRkOk8NoM=",
       "dev": true,
       "requires": {
-        "glob": "3.2.11",
-        "lodash": "2.4.2"
+        "glob": "~3.2.9",
+        "lodash": "~2.4.1"
       },
       "dependencies": {
         "glob": {
@@ -835,8 +835,8 @@
           "integrity": "sha1-Spc/Y1uRkPcV0QmH1cAP0oFevj0=",
           "dev": true,
           "requires": {
-            "inherits": "2.0.3",
-            "minimatch": "0.3.0"
+            "inherits": "2",
+            "minimatch": "0.3"
           }
         },
         "lodash": {
@@ -851,8 +851,8 @@
           "integrity": "sha1-J12O2qxPG7MyZHIInnlJyDlGmd0=",
           "dev": true,
           "requires": {
-            "lru-cache": "2.7.3",
-            "sigmund": "1.0.1"
+            "lru-cache": "2",
+            "sigmund": "~1.0.0"
           }
         }
       }
@@ -863,10 +863,10 @@
       "integrity": "sha1-+oZxTnLCHbiGAXYezy9VXRq8a5Y=",
       "dev": true,
       "requires": {
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@@ -1126,11 +1126,11 @@
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@@ -1148,7 +1148,7 @@
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+        "which": "~1.0.5"
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@@ -1280,7 +1280,7 @@
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-        "hoek": "2.16.3",
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+        "chalk": "^1.0.0",
+        "cli-cursor": "^1.0.1",
+        "cli-width": "^2.0.0",
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+        "lodash": "^4.3.0",
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@@ -1420,7 +1420,7 @@
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       "dev": true,
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@@ -1429,10 +1429,10 @@
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-        "jsonpointer": "4.0.1",
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+        "xtend": "^4.0.0"
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@@ -1447,7 +1447,7 @@
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@@ -1456,7 +1456,7 @@
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@@ -1471,7 +1471,7 @@
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-        "which": "1.3.0",
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+        "abbrev": "1.0.x",
+        "async": "1.x",
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@@ -1538,11 +1538,11 @@
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@@ -1560,7 +1560,7 @@
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@@ -1569,7 +1569,7 @@
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@@ -1578,7 +1578,7 @@
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@@ -1613,8 +1613,8 @@
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@@ -1636,7 +1636,7 @@
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@@ -1689,7 +1689,7 @@
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@@ -1711,8 +1711,8 @@
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       "dev": true,
       "requires": {
-        "prelude-ls": "1.1.2",
-        "type-check": "0.3.2"
+        "prelude-ls": "~1.1.2",
+        "type-check": "~0.3.2"
       }
     },
     "load-grunt-tasks": {
@@ -1721,10 +1721,10 @@
       "integrity": "sha1-ByhWEYD9IP+KaSdQWFL8WKrqDIg=",
       "dev": true,
       "requires": {
-        "arrify": "1.0.1",
-        "multimatch": "2.1.0",
-        "pkg-up": "1.0.0",
-        "resolve-pkg": "0.1.0"
+        "arrify": "^1.0.0",
+        "multimatch": "^2.0.0",
+        "pkg-up": "^1.0.0",
+        "resolve-pkg": "^0.1.0"
       }
     },
     "lodash": {
@@ -1768,7 +1768,7 @@
       "integrity": "sha1-K4WKUuXs1RbbiXrCvodIeDBpjiM=",
       "dev": true,
       "requires": {
-        "mime-db": "1.29.0"
+        "mime-db": "~1.29.0"
       }
     },
     "minimatch": {
@@ -1777,8 +1777,8 @@
       "integrity": "sha1-x054BXT2PG+aCQ6Q775u9TpqdWo=",
       "dev": true,
       "requires": {
-        "lru-cache": "2.7.3",
-        "sigmund": "1.0.1"
+        "lru-cache": "2",
+        "sigmund": "~1.0.0"
       }
     },
     "minimist": {
@@ -1849,8 +1849,8 @@
           "integrity": "sha1-Spc/Y1uRkPcV0QmH1cAP0oFevj0=",
           "dev": true,
           "requires": {
-            "inherits": "2.0.3",
-            "minimatch": "0.3.0"
+            "inherits": "2",
+            "minimatch": "0.3"
           }
         },
         "minimatch": {
@@ -1859,8 +1859,8 @@
           "integrity": "sha1-J12O2qxPG7MyZHIInnlJyDlGmd0=",
           "dev": true,
           "requires": {
-            "lru-cache": "2.7.3",
-            "sigmund": "1.0.1"
+            "lru-cache": "2",
+            "sigmund": "~1.0.0"
           }
         },
         "ms": {
@@ -1894,13 +1894,13 @@
           "integrity": "sha1-BwV6y+JGeyIELTb5jFrVBwVOlbE=",
           "dev": true,
           "requires": {
-            "buffer-shims": "1.0.0",
-            "core-util-is": "1.0.2",
-            "inherits": "2.0.3",
-            "isarray": "1.0.0",
-            "process-nextick-args": "1.0.7",
-            "string_decoder": "1.0.3",
-            "util-deprecate": "1.0.2"
+            "buffer-shims": "~1.0.0",
+            "core-util-is": "~1.0.0",
+            "inherits": "~2.0.1",
+            "isarray": "~1.0.0",
+            "process-nextick-args": "~1.0.6",
+            "string_decoder": "~1.0.0",
+            "util-deprecate": "~1.0.1"
           }
         }
       }
@@ -1911,8 +1911,8 @@
       "integrity": "sha1-HDh3bOsXSZepnCiGDu2QKNqbPho=",
       "dev": true,
       "requires": {
-        "bson": "1.0.4",
-        "require_optional": "1.0.1"
+        "bson": "~1.0.4",
+        "require_optional": "~1.0.0"
       }
     },
     "mongoose": {
@@ -1922,7 +1922,7 @@
       "dev": true,
       "requires": {
         "async": "2.1.4",
-        "bson": "1.0.4",
+        "bson": "~1.0.4",
         "hooks-fixed": "2.0.0",
         "kareem": "1.5.0",
         "mongodb": "2.2.27",
@@ -1941,7 +1941,7 @@
           "integrity": "sha1-LSFgx3iAMuTdbL4lAvH5osj2zeQ=",
           "dev": true,
           "requires": {
-            "lodash": "4.17.4"
+            "lodash": "^4.14.0"
           }
         }
       }
@@ -1990,10 +1990,10 @@
       "integrity": "sha1-nHkGoi+0wCkZ4vX3UWG0zb1LKis=",
       "dev": true,
       "requires": {
-        "array-differ": "1.0.0",
-        "array-union": "1.0.2",
-        "arrify": "1.0.1",
-        "minimatch": "3.0.4"
+        "array-differ": "^1.0.0",
+        "array-union": "^1.0.1",
+        "arrify": "^1.0.0",
+        "minimatch": "^3.0.0"
       },
       "dependencies": {
         "minimatch": {
@@ -2002,7 +2002,7 @@
           "integrity": "sha512-yJHVQEhyqPLUTgt9B83PXu6W3rx4MvvHvSUvToogpwoGDOUQ+yDrR0HRot+yOCdCO7u4hX3pWft6kWBBcqh0UA==",
           "dev": true,
           "requires": {
-            "brace-expansion": "1.1.8"
+            "brace-expansion": "^1.1.7"
           }
         }
       }
@@ -2025,7 +2025,7 @@
       "integrity": "sha1-bd0hvSoxQXuScn3Vhfim83YI6+4=",
       "dev": true,
       "requires": {
-        "abbrev": "1.1.1"
+        "abbrev": "1"
       }
     },
     "number-is-nan": {
@@ -2052,7 +2052,7 @@
       "integrity": "sha1-WDsap3WWHUsROsF9nFC6753Xa9E=",
       "dev": true,
       "requires": {
-        "wrappy": "1.0.2"
+        "wrappy": "1"
       }
     },
     "onetime": {
@@ -2067,8 +2067,8 @@
       "integrity": "sha1-2j6nRob6IaGaERwybpDrFaAZZoY=",
       "dev": true,
       "requires": {
-        "minimist": "0.0.10",
-        "wordwrap": "0.0.3"
+        "minimist": "~0.0.1",
+        "wordwrap": "~0.0.2"
       },
       "dependencies": {
         "minimist": {
@@ -2091,12 +2091,12 @@
       "integrity": "sha1-NkxeQJ0/TWMB1sC0wFu6UBgK62Q=",
       "dev": true,
       "requires": {
-        "deep-is": "0.1.3",
-        "fast-levenshtein": "2.0.6",
-        "levn": "0.3.0",
-        "prelude-ls": "1.1.2",
-        "type-check": "0.3.2",
-        "wordwrap": "1.0.0"
+        "deep-is": "~0.1.3",
+        "fast-levenshtein": "~2.0.4",
+        "levn": "~0.3.0",
+        "prelude-ls": "~1.1.2",
+        "type-check": "~0.3.2",
+        "wordwrap": "~1.0.0"
       }
     },
     "os-homedir": {
@@ -2111,7 +2111,7 @@
       "integrity": "sha1-D+tsZPD8UY2adU3V77YscCJ2H0s=",
       "dev": true,
       "requires": {
-        "pinkie-promise": "2.0.1"
+        "pinkie-promise": "^2.0.0"
       }
     },
     "path-is-absolute": {
@@ -2144,7 +2144,7 @@
       "integrity": "sha1-ITXW36ejWMBprJsXh3YogihFD/o=",
       "dev": true,
       "requires": {
-        "pinkie": "2.0.4"
+        "pinkie": "^2.0.0"
       }
     },
     "pkg-up": {
@@ -2153,7 +2153,7 @@
       "integrity": "sha1-Pgj7RhUlxEIWJKM7n35tCvWwWiY=",
       "dev": true,
       "requires": {
-        "find-up": "1.1.2"
+        "find-up": "^1.0.0"
       }
     },
     "pluralize": {
@@ -2198,13 +2198,13 @@
       "integrity": "sha512-m+qzzcn7KUxEmd1gMbchF+Y2eIUbieUaxkWtptyHywrX0rE8QEYqPC07Vuy4Wm32/xE16NcdBctb8S0Xe/5IeQ==",
       "dev": true,
       "requires": {
-        "core-util-is": "1.0.2",
-        "inherits": "2.0.3",
-        "isarray": "1.0.0",
-        "process-nextick-args": "1.0.7",
-        "safe-buffer": "5.1.1",
-        "string_decoder": "1.0.3",
-        "util-deprecate": "1.0.2"
+        "core-util-is": "~1.0.0",
+        "inherits": "~2.0.3",
+        "isarray": "~1.0.0",
+        "process-nextick-args": "~1.0.6",
+        "safe-buffer": "~5.1.1",
+        "string_decoder": "~1.0.3",
+        "util-deprecate": "~1.0.1"
       }
     },
     "readline2": {
@@ -2213,8 +2213,8 @@
       "integrity": "sha1-QQWWCP/BVHV7cV2ZidGZ/783LjU=",
       "dev": true,
       "requires": {
-        "code-point-at": "1.1.0",
-        "is-fullwidth-code-point": "1.0.0",
+        "code-point-at": "^1.0.0",
+        "is-fullwidth-code-point": "^1.0.0",
         "mute-stream": "0.0.5"
       }
     },
@@ -2236,26 +2236,26 @@
       "integrity": "sha1-Tf5b9r6LjNw3/Pk+BLZVd3InEN4=",
       "dev": true,
       "requires": {
-        "aws-sign2": "0.6.0",
-        "aws4": "1.6.0",
-        "caseless": "0.11.0",
-        "combined-stream": "1.0.5",
-        "extend": "3.0.1",
-        "forever-agent": "0.6.1",
-        "form-data": "2.1.4",
-        "har-validator": "2.0.6",
-        "hawk": "3.1.3",
-        "http-signature": "1.1.1",
-        "is-typedarray": "1.0.0",
-        "isstream": "0.1.2",
-        "json-stringify-safe": "5.0.1",
-        "mime-types": "2.1.16",
-        "oauth-sign": "0.8.2",
-        "qs": "6.3.2",
-        "stringstream": "0.0.5",
-        "tough-cookie": "2.3.2",
-        "tunnel-agent": "0.4.3",
-        "uuid": "3.1.0"
+        "aws-sign2": "~0.6.0",
+        "aws4": "^1.2.1",
+        "caseless": "~0.11.0",
+        "combined-stream": "~1.0.5",
+        "extend": "~3.0.0",
+        "forever-agent": "~0.6.1",
+        "form-data": "~2.1.1",
+        "har-validator": "~2.0.6",
+        "hawk": "~3.1.3",
+        "http-signature": "~1.1.0",
+        "is-typedarray": "~1.0.0",
+        "isstream": "~0.1.2",
+        "json-stringify-safe": "~5.0.1",
+        "mime-types": "~2.1.7",
+        "oauth-sign": "~0.8.1",
+        "qs": "~6.3.0",
+        "stringstream": "~0.0.4",
+        "tough-cookie": "~2.3.0",
+        "tunnel-agent": "~0.4.1",
+        "uuid": "^3.0.0"
       }
     },
     "require-uncached": {
@@ -2264,8 +2264,8 @@
       "integrity": "sha1-Tg1W1slmL9MeQwEcS5WqSZVUIdM=",
       "dev": true,
       "requires": {
-        "caller-path": "0.1.0",
-        "resolve-from": "1.0.1"
+        "caller-path": "^0.1.0",
+        "resolve-from": "^1.0.0"
       }
     },
     "require_optional": {
@@ -2274,8 +2274,8 @@
       "integrity": "sha512-qhM/y57enGWHAe3v/NcwML6a3/vfESLe/sGM2dII+gEO0BpKRUkWZow/tyloNqJyN6kXSl3RyyM8Ll5D/sJP8g==",
       "dev": true,
       "requires": {
-        "resolve-from": "2.0.0",
-        "semver": "5.4.1"
+        "resolve-from": "^2.0.0",
+        "semver": "^5.1.0"
       },
       "dependencies": {
         "resolve-from": {
@@ -2304,7 +2304,7 @@
       "integrity": "sha1-AsyZNBDik2livZcWahsHfalyVTE=",
       "dev": true,
       "requires": {
-        "resolve-from": "2.0.0"
+        "resolve-from": "^2.0.0"
       },
       "dependencies": {
         "resolve-from": {
@@ -2321,8 +2321,8 @@
       "integrity": "sha1-NGYfRohjJ/7SmRR5FSJS35LapUE=",
       "dev": true,
       "requires": {
-        "exit-hook": "1.1.1",
-        "onetime": "1.1.0"
+        "exit-hook": "^1.0.0",
+        "onetime": "^1.0.0"
       }
     },
     "right-align": {
@@ -2332,7 +2332,7 @@
       "dev": true,
       "optional": true,
       "requires": {
-        "align-text": "0.1.4"
+        "align-text": "^0.1.1"
       }
     },
     "rimraf": {
@@ -2347,7 +2347,7 @@
       "integrity": "sha1-yK1KXhEGYeQCp9IbUw4AnyX444k=",
       "dev": true,
       "requires": {
-        "once": "1.4.0"
+        "once": "^1.3.0"
       }
     },
     "rx-lite": {
@@ -2395,7 +2395,7 @@
         "formatio": "1.1.1",
         "lolex": "1.3.2",
         "samsam": "1.1.2",
-        "util": "0.10.3"
+        "util": ">=0.10.3 <1"
       }
     },
     "slice-ansi": {
@@ -2416,7 +2416,7 @@
       "integrity": "sha1-ZUEYTMkK7qbG57NeJlkIJEPGYZg=",
       "dev": true,
       "requires": {
-        "hoek": "2.16.3"
+        "hoek": "2.x.x"
       }
     },
     "source-map": {
@@ -2426,7 +2426,7 @@
       "dev": true,
       "optional": true,
       "requires": {
-        "amdefine": "1.0.1"
+        "amdefine": ">=0.0.4"
       }
     },
     "sprintf-js": {
@@ -2441,14 +2441,14 @@
       "integrity": "sha1-US322mKHFEMW3EwY/hzx2UBzm+M=",
       "dev": true,
       "requires": {
-        "asn1": "0.2.3",
-        "assert-plus": "1.0.0",
-        "bcrypt-pbkdf": "1.0.1",
-        "dashdash": "1.14.1",
-        "ecc-jsbn": "0.1.1",
-        "getpass": "0.1.7",
-        "jsbn": "0.1.1",
-        "tweetnacl": "0.14.5"
+        "asn1": "~0.2.3",
+        "assert-plus": "^1.0.0",
+        "bcrypt-pbkdf": "^1.0.0",
+        "dashdash": "^1.12.0",
+        "ecc-jsbn": "~0.1.1",
+        "getpass": "^0.1.1",
+        "jsbn": "~0.1.0",
+        "tweetnacl": "~0.14.0"
       },
       "dependencies": {
         "assert-plus": {
@@ -2465,9 +2465,9 @@
       "integrity": "sha1-EYvfW4zcUaKn5w0hHgfisLmxB9M=",
       "dev": true,
       "requires": {
-        "code-point-at": "1.1.0",
-        "is-fullwidth-code-point": "1.0.0",
-        "strip-ansi": "3.0.1"
+        "code-point-at": "^1.0.0",
+        "is-fullwidth-code-point": "^1.0.0",
+        "strip-ansi": "^3.0.0"
       }
     },
     "string_decoder": {
@@ -2476,7 +2476,7 @@
       "integrity": "sha512-4AH6Z5fzNNBcH+6XDMfA/BTt87skxqJlO0lAh3Dker5zThcAxG6mKz+iGu308UKoPPQ8Dcqx/4JhujzltRa+hQ==",
       "dev": true,
       "requires": {
-        "safe-buffer": "5.1.1"
+        "safe-buffer": "~5.1.0"
       }
     },
     "stringstream": {
@@ -2491,7 +2491,7 @@
       "integrity": "sha1-ajhfuIU9lS1f8F0Oiq+UJ43GPc8=",
       "dev": true,
       "requires": {
-        "ansi-regex": "2.1.1"
+        "ansi-regex": "^2.0.0"
       }
     },
     "strip-json-comments": {
@@ -2512,12 +2512,12 @@
       "integrity": "sha1-K7xULw/amGGnVdOUf+/Ys/UThV8=",
       "dev": true,
       "requires": {
-        "ajv": "4.11.8",
-        "ajv-keywords": "1.5.1",
-        "chalk": "1.1.3",
-        "lodash": "4.17.4",
+        "ajv": "^4.7.0",
+        "ajv-keywords": "^1.0.0",
+        "chalk": "^1.1.1",
+        "lodash": "^4.0.0",
         "slice-ansi": "0.0.4",
-        "string-width": "2.1.1"
+        "string-width": "^2.0.0"
       },
       "dependencies": {
         "ansi-regex": {
@@ -2538,8 +2538,8 @@
           "integrity": "sha512-nOqH59deCq9SRHlxq1Aw85Jnt4w6KvLKqWVik6oA9ZklXLNIOlqg4F2yrT1MVaTjAqvVwdfeZ7w7aCvJD7ugkw==",
           "dev": true,
           "requires": {
-            "is-fullwidth-code-point": "2.0.0",
-            "strip-ansi": "4.0.0"
+            "is-fullwidth-code-point": "^2.0.0",
+            "strip-ansi": "^4.0.0"
           }
         },
         "strip-ansi": {
@@ -2548,7 +2548,7 @@
           "integrity": "sha1-qEeQIusaw2iocTibY1JixQXuNo8=",
           "dev": true,
           "requires": {
-            "ansi-regex": "3.0.0"
+            "ansi-regex": "^3.0.0"
           }
         }
       }
@@ -2577,7 +2577,7 @@
       "integrity": "sha1-8IH3bkyFcg5sN6X6ztc3FQ2EByo=",
       "dev": true,
       "requires": {
-        "punycode": "1.4.1"
+        "punycode": "^1.4.1"
       }
     },
     "tryit": {
@@ -2605,7 +2605,7 @@
       "integrity": "sha1-WITKtRLPHTVeP7eE8wgEsrUg23I=",
       "dev": true,
       "requires": {
-        "prelude-ls": "1.1.2"
+        "prelude-ls": "~1.1.2"
       }
     },
     "type-detect": {
@@ -2627,9 +2627,9 @@
       "dev": true,
       "optional": true,
       "requires": {
-        "source-map": "0.5.6",
-        "uglify-to-browserify": "1.0.2",
-        "yargs": "3.10.0"
+        "source-map": "~0.5.1",
+        "uglify-to-browserify": "~1.0.0",
+        "yargs": "~3.10.0"
       },
       "dependencies": {
         "source-map": {
@@ -2666,7 +2666,7 @@
       "integrity": "sha1-nHC/2Babwdy/SGBODwS4tJzenp8=",
       "dev": true,
       "requires": {
-        "os-homedir": "1.0.2"
+        "os-homedir": "^1.0.0"
       }
     },
     "util": {
@@ -2704,9 +2704,9 @@
       "integrity": "sha1-OhBcoXBTr1XW4nDB+CiGguGNpAA=",
       "dev": true,
       "requires": {
-        "assert-plus": "1.0.0",
+        "assert-plus": "^1.0.0",
         "core-util-is": "1.0.2",
-        "extsprintf": "1.3.0"
+        "extsprintf": "^1.2.0"
       },
       "dependencies": {
         "assert-plus": {
@@ -2748,7 +2748,7 @@
       "integrity": "sha1-X8A4KOJkzqP+kUVUdvejxWbLB1c=",
       "dev": true,
       "requires": {
-        "mkdirp": "0.5.1"
+        "mkdirp": "^0.5.1"
       }
     },
     "xtend": {
@@ -2764,9 +2764,9 @@
       "dev": true,
       "optional": true,
       "requires": {
-        "camelcase": "1.2.1",
-        "cliui": "2.1.0",
-        "decamelize": "1.2.0",
+        "camelcase": "^1.0.2",
+        "cliui": "^2.1.0",
+        "decamelize": "^1.0.0",
         "window-size": "0.1.0"
       }
     }
diff --git a/test/base.js b/test/base.js
index 709cdcb..2be2cb8 100644
--- a/test/base.js
+++ b/test/base.js
@@ -303,39 +303,39 @@ describe('Basic => ', function() {
 
         });
 
-        describe('a counter which referes others fields => ', function() {
+        describe('a counter which referes others fields => ', function () {
 
-            before(function() {
+            before(function () {
                 var ComposedSchema = new Schema({
-                    country: String,
+                    country: Schema.Types.ObjectId,
                     city: String,
                     inhabitant: Number
                 });
-                ComposedSchema.plugin(AutoIncrement, {id: 'inhabitant_counter', inc_field: 'inhabitant', reference_fields: ['country', 'city']});
+                ComposedSchema.plugin(AutoIncrement, { id: 'inhabitant_counter', inc_field: 'inhabitant', reference_fields: ['city', 'country'] });
                 this.Composed = mongoose.model('Composed', ComposedSchema);
             });
 
-            it('increment on save', function(done) {
-                var t = new this.Composed({country:'France', city:'Paris'});
-                t.save(function(err) {
+            it('increment on save', function (done) {
+                var t = new this.Composed({ country: mongoose.Types.ObjectId('59c380f51207391238e7f3f2'), city: 'Paris' });
+                t.save(function (err) {
                     if (err) return done(err);
                     assert.deepEqual(t.inhabitant, 1);
                     done();
                 });
             });
 
-            it('saving a document with the same reference increment the counter', function(done) {
-                var t = new this.Composed({country:'France', city:'Paris'});
-                t.save(function(err) {
+            it('saving a document with the same reference increment the counter', function (done) {
+                var t = new this.Composed({ country: mongoose.Types.ObjectId('59c380f51207391238e7f3f2'), city: 'Paris' });
+                t.save(function (err) {
                     if (err) return done(err);
                     assert.deepEqual(t.inhabitant, 2);
                     done();
                 });
             });
 
-            it('saving with a different reference do not increment the counter', function(done) {
-                var t = new this.Composed({country:'USA', city:'New York'});
-                t.save(function(err) {
+            it('saving with a different reference do not increment the counter', function (done) {
+                var t = new this.Composed({ country: mongoose.Types.ObjectId('59c380f51207391238e7f3f2'), city: 'Carcasonne' });
+                t.save(function (err) {
                     if (err) return done(err);
                     assert.deepEqual(t.inhabitant, 1);
                     done();