diff --git a/lib/model/Device.js b/lib/model/Device.js
index c8f6db84a..d55b120d4 100644
--- a/lib/model/Device.js
+++ b/lib/model/Device.js
@@ -23,6 +23,9 @@
 
 const mongoose = require('mongoose');
 const Schema = mongoose.Schema;
+const Group = require('./Group');
+
+mongoose.Schema.Types.ExplicitAttrsType = Group.ExplicitAttrsType;
 
 const Device = new Schema({
     id: String,
@@ -49,7 +52,7 @@ const Device = new Schema({
     internalAttributes: Object,
     autoprovision: Boolean,
     expressionLanguage: String,
-    explicitAttrs: Boolean,
+    explicitAttrs: Group.ExplicitAttrsType,
     ngsiVersion: String,
     cache: Boolean
 });
diff --git a/lib/model/Group.js b/lib/model/Group.js
index 10b48c0bd..f440fbc22 100644
--- a/lib/model/Group.js
+++ b/lib/model/Group.js
@@ -24,6 +24,23 @@
 const mongoose = require('mongoose');
 const Schema = mongoose.Schema;
 
+class ExplicitAttrsType extends mongoose.SchemaType {
+    constructor(key, options) {
+        super(key, options, 'ExplicitAttrsType');
+    }
+    // `cast()` takes a parameter that can be anything. You need to
+    // validate the provided `val` and throw a `CastError` if you
+    // can't convert it.
+    cast(val) {
+        if (!(typeof val === 'boolean' || typeof val === 'string')) {
+            throw new Error('ExplicitAttrsType: ' + val + ' is not Boolean or String');
+        }
+        return val;
+    }
+}
+
+mongoose.Schema.Types.ExplicitAttrsType = ExplicitAttrsType;
+
 const Group = new Schema({
     url: String,
     resource: String,
@@ -43,9 +60,10 @@ const Group = new Schema({
     internalAttributes: Array,
     autoprovision: Boolean,
     expressionLanguage: String,
-    explicitAttrs: Boolean,
+    explicitAttrs: ExplicitAttrsType,
     defaultEntityNameConjunction: String,
     ngsiVersion: String,
+    entityNameExp: String,
     cache: Boolean
 });
 
@@ -56,3 +74,4 @@ function load(db) {
 }
 
 module.exports.load = load;
+module.exports.ExplicitAttrsType = ExplicitAttrsType;