查询¶

Documents can be retrieved through several static helper methods of models.

Any model method which involves specifying query conditions can be executed two ways:

When a callback function:

is passed, the operation will be executed immediately with the results passed to the callback.
is not passed, an instance of Query is returned, which provides a special query builder interface.

A Query has a .then() function, and thus can be used as a promise.

When executing a query with a callback function, you specify your query as a JSON document. The JSON document's syntax is the same as the MongoDB shell.

var Person = mongoose.model('Person', yourSchema);


Person.findOne({ 'name.last': 'Ghost' }, 'name occupation', function (err, person) {
  if (err) return handleError(err);

  console.log('%s %s is a %s.', person.name.first, person.name.last,
    person.occupation);
});

Here we see that the query was executed immediately and the results passed to our callback. All callbacks in Mongoose use the pattern: callback(error, result). If an error occurs executing the query, the error parameter will contain an error document, and result will be null. If the query is successful, the error parameter will be null, and the result will be populated with the results of the query.

Anywhere a callback is passed to a query in Mongoose, the callback follows the pattern callback(error, results). What results is depends on the operation: For findOne() it is a potentially-null single document, find() a list of documents, count() the number of documents, update() the number of documents affected, etc. The API docs for Models provide more detail on what is passed to the callbacks.

Now let's look at what happens when no callback is passed:

var query = Person.findOne({ 'name.last': 'Ghost' });


query.select('name occupation');


query.exec(function (err, person) {
  if (err) return handleError(err);

  console.log('%s %s is a %s.', person.name.first, person.name.last,
    person.occupation);
});

In the above code, the query variable is of type Query. A Query enables you to build up a query using chaining syntax, rather than specifying a JSON object. The below 2 examples are equivalent.

Person.
  find({
    occupation: /host/,
    'name.last': 'Ghost',
    age: { $gt: 17, $lt: 66 },
    likes: { $in: ['vaporizing', 'talking'] }
  }).
  limit(10).
  sort({ occupation: -1 }).
  select({ name: 1, occupation: 1 }).
  exec(callback);


Person.
  find({ occupation: /host/ }).
  where('name.last').equals('Ghost').
  where('age').gt(17).lt(66).
  where('likes').in(['vaporizing', 'talking']).
  limit(10).
  sort('-occupation').
  select('name occupation').
  exec(callback);

A full list of Query helper functions can be found in the API docs.

参考其他文件 ¶

There are no joins in MongoDB but sometimes we still want references to documents in other collections. This is where population comes in. Read more about how to include documents from other collections in your query results here.

流 ¶

You can stream query results from MongoDB. You need to call the Query#cursor() function to return an instance of QueryCursor.

var cursor = Person.find({ occupation: /host/ }).cursor();
cursor.on('data', function(doc) {

});
cursor.on('close', function() {

});

查询¶

参考其他文件¶

流¶

参考其他文件 ¶

流 ¶