[MongoDB] Query, update, index and group

最新推荐文章于 2025-03-20 18:28:59 发布

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最新推荐文章于 2025-03-20 18:28:59 发布

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文章标签：数据库

本文深入探讨了数据库操作的关键概念，包括查询操作如使用$in、$where等运算符进行条件筛选，以及更新操作如修改文档属性和批量更新。同时，文章强调了性能优化和索引构建的重要性，通过创建索引来提升查询效率。此外，还介绍了聚合操作在汇总数据方面的应用，以及如何利用$group进行复杂的数据分组和计算。

/*
    1. Query Operators
*/
db.posts.find({
    viewsCount: {$get: 1000, $lte: 3000}
}, {_id: 0, viewsCount: 1, title: 1})

// $in
db.posts.find({
    categories: {$in: ['ios']}
}, {categories: 1})

//$where
db.posts.find({
    $where: function(){
        return this.categories.length>15
    }
}, {categories: 1, title: 1})

//see how many categories from previous query:
db.posts.find({
    $where: function(){
        return this.categories.length>15
    }
}, {categories: 1, title: 1})[0].categories.length

Update:

/*
    2. Update
*/
var d = db.posts.findOne();
//change the author email:
d.author.email = "new@new.com"
//update the database
db.post.update({_id: d._id}, d);


//update mutli-document
db.posts.update({viewsCount: {$gt: 3000}}, {$set: {newKey: true}}, {multi:true}) //add new key, set mutli

Performance and indexes:

/*
    3. Performance and indexes
*/
//create the data
db.numbers.drop();
var num = 5000000,
i = 0;
 for(i = 0; i < num; i ++){
    var randomNumber = Math.floor(Math.random()*10000);
    db.numbers.insert({number:randomNumber});
    //print(i);
 }

db.number.find({number: {$gt: 1000, $lt: 3000}, {_id: 0, number: 1}}).explain(); //it scan all the doucment, took 3500ms
 
//add index:
db.numbers.ensureIndex({number: 1});
//took 1046 ms, scan 1m instead of 5m

Group:

/*
    4. $group
*/

//sum up the viewCount, rename the result as 'totalViewsCount'
db.posts.aggregate({
    $group: {
        _id:null,
        totalViewsCount: {$sum: '$viewsCount'}
    }
})

//adding 1 for each document
db.posts.aggregate({
    $group: {
        _id:null,
        totalNumberOfDocuments: {$sum: 1}
    }
})

// =
db.posts.count()