Improve "filter" arg description

Add an example showing how to serialize object values as JSON.

Author: Raymond Camden

lib/persisted-model.js

@@ -749,7 +749,9 @@ module.exports = function(registry) {
         { arg: 'id', type: 'any', description: 'Model id', required: true,
           http: {source: 'path'}},
         {arg: 'filter', type: 'object',
-          description: 'Filter defining fields and include'},
+          description:
+          'Filter defining fields and include - must be a JSON-encoded string (' +
+          '{"something":"value"})'},
         {arg: 'options', type: 'object', http: 'optionsFromRequest'},
       ]),
       returns: {arg: 'data', type: typeName, root: true},
@@ -782,7 +784,8 @@ module.exports = function(registry) {
       accessType: 'READ',
       accepts: this._removeOptionsArgIfDisabled([
         {arg: 'filter', type: 'object', description:
-          'Filter defining fields, where, include, order, offset, and limit'},
+        'Filter defining fields, where, include, order, offset, and limit - must be a ' +
+        'JSON-encoded string ({"something":"value"})'},
         {arg: 'options', type: 'object', http: 'optionsFromRequest'},
       ]),
       returns: {arg: 'data', type: [typeName], root: true},
@@ -794,7 +797,8 @@ module.exports = function(registry) {
       accessType: 'READ',
       accepts: this._removeOptionsArgIfDisabled([
         {arg: 'filter', type: 'object', description:
-          'Filter defining fields, where, include, order, offset, and limit'},
+        'Filter defining fields, where, include, order, offset, and limit - must be a ' +
+        'JSON-encoded string ({"something":"value"})'},
         {arg: 'options', type: 'object', http: 'optionsFromRequest'},
       ]),
       returns: {arg: 'data', type: typeName, root: true},