Map exists to HEAD for REST

lib/models/model.js

@@ -418,7 +418,22 @@ Model.hasManyRemoting = function (relationName, relation, define) {
         description: 'Foreign key for ' + relationName, required: true,
         http: {source: 'path'}},
       description: 'Check the existence of ' + relationName + ' relation to an item by id',
-      returns: {}
+      returns: {arg: 'exists', type: 'boolean', root: true},
+      rest: {
+        // After hook to map exists to 200/404 for HEAD
+        after: function(ctx, cb) {
+          if(ctx.result === false) {
+            var modelName = ctx.method.sharedClass.name;
+            var id = ctx.getArgByName('id');
+            var msg = 'Unknown "' + modelName + '" id "' + id + '".';
+            var error = new Error(msg);
+            error.statusCode = error.status = 404;
+            cb(error);
+          } else {
+            cb();
+          }
+        }
+      }
     }, existsFunc);
   }
 };

test/relations.integration.js

@@ -213,6 +213,45 @@ describe('relations - integration', function () {
       });
     });
 
+    describe('HEAD /physicians/:id/patients/rel/:fk', function () {
+
+      before(function (done) {
+        var self = this;
+        setup(true, function (err, root) {
+          self.url = root.relUrl;
+          self.patient = root.patient;
+          self.physician = root.physician;
+          done();
+        });
+      });
+
+      lt.describe.whenCalledRemotely('HEAD', '/api/physicians/:id/patients/rel/:fk', function () {
+        it('should succeed with statusCode 200', function () {
+          assert.equal(this.res.statusCode, 200);
+        });
+      });
+    });
+
+    describe('HEAD /physicians/:id/patients/rel/:fk that does not exist', function () {
+
+      before(function (done) {
+        var self = this;
+        setup(true, function (err, root) {
+          self.url = '/api/physicians/' + root.physician.id
+            + '/patients/rel/' + '999';
+          self.patient = root.patient;
+          self.physician = root.physician;
+          done();
+        });
+      });
+
+      lt.describe.whenCalledRemotely('HEAD', '/api/physicians/:id/patients/rel/:fk', function () {
+        it('should succeed with statusCode 404', function () {
+          assert.equal(this.res.statusCode, 404);
+        });
+      });
+    });
+
     describe('DELETE /physicians/:id/patients/rel/:fk', function () {
 
       before(function (done) {