Sorting by arbitrary field about graffiti-mongoose HOT 16 CLOSED

diff --git a/src/e2e.spec.js b/src/e2e.spec.js
index 1f70233..630ca62 100644
--- a/src/e2e.spec.js
+++ b/src/e2e.spec.js
@@ -268,6 +268,46 @@ describe('e2e', () => {
           {node: {name: 'Foo'}}
         ]);
       });
+
+      it('should return results in ascending order', async function Test() {
+        const result = await graphql(schema, `{
+          viewer {
+            users(orderBy: nameAsc) {
+              edges {
+                node {
+                  name
+                }
+              }
+            }
+          }
+        }`);
+
+        expect(result.data.viewer.users.edges).to.be.eql([
+          { node: { name: 'Bar' } },
+          { node: { name: 'Foo' } },
+          { node: { name: 'Mother' } }
+        ]);
+      });
+
+      it('should return results in descending order', async function Test() {
+        const result = await graphql(schema, `{
+          viewer {
+            users(orderBy: nameDesc) {
+              edges {
+                node {
+                  name
+                }
+              }
+            }
+          }
+        }`);
+
+        expect(result.data.viewer.users.edges).to.be.eql([
+          { node: { name: 'Mother' } },
+          { node: { name: 'Foo' } },
+          { node: { name: 'Bar' } }
+        ]);
+      });
     });

     describe('mutations', () => {
diff --git a/src/query/query.js b/src/query/query.js
index 1e8b766..0b5f5c5 100644
--- a/src/query/query.js
+++ b/src/query/query.js
@@ -255,7 +255,7 @@ async function connectionFromModel(graffitiModel, args, info) {
     return emptyConnection();
   }

-  const {before, after, first, last, id, ...selector} = args;
+  const {before, after, first, last, id, orderBy, ...selector} = args;

   const begin = getId(after);
   const end = getId(before);
@@ -277,10 +277,17 @@ async function connectionFromModel(graffitiModel, args, info) {
     selector._id.$lt = end;
   }

+  let sort = {_id: 1};
+  if (orderBy){
+    sort = {
+      [orderBy.slice(0,-3)]: orderBy.endsWith('Asc') ? 1 : -1
+    };
+  }
+
   const result = await getList(Collection, selector, {
     skip: offset,
     limit: limit,
-    sort: {_id: 1}
+    sort
   }, info);
   const count = await getCount(Collection, selector);

diff --git a/src/type/type.js b/src/type/type.js
index 473e202..cc8c6d9 100644
--- a/src/type/type.js
+++ b/src/type/type.js
@@ -11,6 +11,7 @@ import {
 } from 'graphql-relay';
 import {
   GraphQLString,
+  GraphQLEnumType,
   GraphQLFloat,
   GraphQLBoolean,
   GraphQLID,
@@ -77,14 +78,37 @@ function setTypeFields(type, fields) {
   type._typeConfig.fields = () => fields;
 }

+const orderByTypes = {};
+function getOrderByType(typeName, fields) {
+  if (!orderByTypes[typeName]){
+    orderByTypes[typeName] = new GraphQLEnumType({
+      name: typeName+"_orderBy",
+      values: reduce(fields, (values, field) => {
+        if (field.type instanceof GraphQLScalarType){
+          values[field.name+"Asc"] = { };
+          values[field.name+"Desc"] = { };
+        }
+        return values;
+      }, {})
+    });
+  }
+  return orderByTypes[typeName];
+}
+
 function getArguments(type, args = {}) {
   const fields = getTypeFields(type);
+
+  fields.orderBy = {
+    name: 'orderBy',
+    type: getOrderByType(type.name, fields)
+  };
+
   return reduce(fields, (args, field) => {
     if (field.type instanceof GraphQLNonNull && field.name !== 'id') {
       field.type = field.type.ofType;
     }

-    if (field.type instanceof GraphQLScalarType) {
+    if (field.type instanceof GraphQLScalarType || field.type instanceof GraphQLEnumType) {
       args[field.name] = field;
     }