Implement distinct field option for select

lib/controller.js

@@ -45,6 +45,18 @@ class Controller extends DataService {
       this.actions.select,
     );
 
+    this.actions.distinct = _.merge(
+      {},
+      _.omit(this.actions.default, 'orderBy'),
+      {
+        method: ['get', 'head'],
+        handler: 'distinct',
+        name: 'distinct',
+        path: 'distinct/:distinctField'
+      },
+      this.actions.distinct
+    );
+
     this.actions.count = _.merge(
       {},
       this.actions.select,

lib/data-service.js

@@ -98,6 +98,46 @@ class DataService {
       .then(collection => this._handlePostForCollection(collection, scope));
   }
 
+  distinct(scope) {
+    return Bb
+      .try(this._handlePre.bind(this, scope))
+      .then(() => {
+        // pick distinctField value to avoid filter affecting
+        scope.context.distinctField = scope.req.params.distinctField;
+        delete scope.req.params.distinctField;
+      })
+      .then(this.getFilter.bind(this, scope))
+      .then((filter) => {
+        // field list
+        scope.fieldList = this.extractFieldList(scope);
+        // q
+        const q = scope.getQ();
+        // orderBy
+        const orderBy = this.getOrderBy(scope);
+        const pagination = scope.pagination = this.getPagination(scope);
+        const distinctField = scope.context.distinctField;
+
+        return this.dataSource.find({
+          distinctField: distinctField,
+          filter: filter,
+          fields: scope.fieldList,
+          q: q,
+          qFields: this.qFields,
+          limit: pagination.limit,
+          skip: (pagination.page - 1) * pagination.limit,
+          queryPipe: this.queryPipe ? (query) => {
+              this.queryPipe(query, scope);
+            } : undefined
+        });
+      })
+      .then((collection) => {
+        return this._handleCollectionPost(collection, scope);
+      })
+      .then((collection) => {
+        return this._handlePostForCollection(collection, scope);
+      });
+  }
+
   selectOne(scope) {
     return this
       .locateModel(scope, true, true)

lib/scope.js

@@ -6,6 +6,7 @@
 
 const ACTIONS = {
   SELECT: 'select',
+  DISTINCT: 'distinct',
   SELECT_ONE: 'selectOne',
   INSERT: 'insert',
   REPLACE: 'replace',
@@ -40,7 +41,11 @@ class RestifizerScope {
   }
 
   isSelect() {
-    return this.checkActionName(ACTIONS.SELECT, ACTIONS.SELECT_ONE, ACTIONS.COUNT);
+    return this.checkActionName(ACTIONS.SELECT, ACTIONS.SELECT_ONE, ACTIONS.COUNT, ACTIONS.DISTINCT);
+  }
+
+  isSelectDistinct() {
+    return this.checkActionName(ACTIONS.DISTINCT);
   }
 
   isChanging() {