// Definition (placed in Scheme)
ProductSchema.scope('available').where('available').equals(true);
ProductSchema.scope('mostRecent', function(count) {
  return this.sort('-updatedAt').limit(count);
});
ProductSchema.scope('category', function(cat) {
  return this.where('category').equals(cat);
};
// etc

// Usage (called from anywhere)
Product.category('men').available().mostRecent(10);
User.male().olderThan(18).sortByAge().populateProfile();
Task.assignedTo(john).highPriority().project('mongoose').limit(5);

var namedScopesPlugin = require('mongoose-named-scopes');

// For one Schema
UserSchema.plugin(namedScopesPlugin);

// For all Schemas at once
mongoose.plugin(namedScopesPlugin);

// You can define scopes by chaining operator calls
UserSchema.scope('male').where('gender').equals('male');

// Or you can pass a function, for when you want to have parameters
// or need to use other statements
UserSchema.scope('olderThan', function (age) {
  // Be sure to return `this`!
  return this.where('age').gt(age);
});

UserSchema.scope('youngerThan', function (age) {
  return this.where('age').lt(age);
});

// Scopes can make use of other scopes!
UserSchema.scope('twenties').olderThan(19).youngerThan(30);

// Heads up! We need to implement this by passing a function so that the
// date parameter gets evaluated when you actually call the scope
UserSchema.scope('active', function () {
  const yesterday = +new Date() - 24*60*60*1000;
  return this.where('lastLogin').gte(yesterday);
});

// You can specify more operators
User.populate('children').olderThan(50).sort('age'); // ...

// Returning array results
User.olderThan(20).exec().then((users) => {}).catch(err);

// Returning single results
User.olderThan(100).findOne().exec().then((users) => {}).catch(err);