MongoDB高级查询

Node+Mongoose常用查询中文文档

推荐看这三篇 mongodb的查询，以及nodejs和mongoose联用的情况

看完mongoose的基本查询就没问题了

如何在mongodb中使用索引？

MongoDB组合索引的优化

非常好的文章，将索引，排序等问题的性能优劣取舍讲的很透彻

explain方法若出现BasicCursor可以视为警告，它意味着MongoDB将对数据集做一个完全的扫描。当数据集里包含上千万条信息时，这完全是行不通的。因此要考虑加上适当的索引

常用的关键字， count, distinct, group ....

mongoose中的2中操作方法，

callback and query returned

Queries

Documents can be retrieved through several static helper methods of .

Any method which 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 is returned, which provides a special QueryBuilder interface for you.

Let's take a look at what happens when passing a callback:

var Person = mongoose.model('Person', yourSchema); // Query// find each person with a last name matching 'Ghost', selecting the `name` and `occupation` fieldsPerson.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) // Space Ghost is a talk show host.})

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 errorparameter will contain an error document, and result will be null. If the query is successful, the errorparameter will be null, and the result will be populated with the results of the query.

Anywhere a callback is passed to a function in Mongoose, the callback follows the patterncallback(error, results).

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

// find each person with a last name matching 'Ghost'var query = Person.findOne({ 'name.last': 'Ghost' });// selecting the `name` and `occupation` fieldsquery.select('name occupation');// execute the query at a later timequery.exec(function (err, person) {
      if (err) return handleError(err);  console.log('%s %s is a %s.', person.name.first, person.name.last, person.occupation) // Space Ghost is a talk show host.})

An instance of was returned which allows us to build up our query. Taking this example further:

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);

转载于:https://www.cnblogs.com/vincedotnet/p/3538337.html

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