如何获取mongoose.js中的最新和最旧记录(或者只是它们之间的时间跨度) [英] How to get the latest and oldest record in mongoose.js (or just the timespan between them)
问题描述
我有一堆记录,我需要得到最新的(最近的)和最旧的(最近的)。
I have a bunch of records and I need to get latest (most recent) and the oldest (least recent).
谷歌搜索时发现这个主题我看到了几个问题:
When googling I found this topic where I saw a couple of queries:
// option 1
Tweet.findOne({}, [], { $orderby : { 'created_at' : -1 } }, function(err, post) {
console.log( post );
});
// option 2
Tweet.find({}, [], {sort:[['arrival',-1]]}, function(err, post) {
console.log( post );
});
不幸的是他们都错了:
TypeError: Invalid select() argument. Must be a string or object.
链接也有这个:
Tweet.find().sort('_id','descending').limit(15).find(function(err, post) {
console.log( post );
});
且一个错误:
TypeError: Invalid sort() argument. Must be a string or object.
那我怎样才能获得这些记录?
So how can I get those records?
更理想的是,我只想要最旧和最新记录之间的时间差(秒?),但我不知道如何开始制作像这样的查询。
Even more ideally I just want the difference in time (seconds?) between the oldest and the newest record, but I have no clue on how to start making a query like that.
这是架构:
var Tweet = new Schema({
body: String
, fid: { type: String, index: { unique: true } }
, username: { type: String, index: true }
, userid: Number
, created_at: Date
, source: String
});
我很确定我拥有最新版本的mongoDB和mongoose。
I'm pretty sure I have the most recent version of mongoDB and mongoose.
这是根据JohnnyHK提供的答案计算时间跨度的方式:
This is how I calc the timespan based on the answer provided by JohnnyHK:
var calcDays = function( cb ) {
var getOldest = function( cb ) {
Tweet.findOne({}, {}, { sort: { 'created_at' : 1 } }, function(err, post) {
cb( null, post.created_at.getTime() );
});
}
, getNewest = function( cb ) {
Tweet.findOne({}, {}, { sort: { 'created_at' : -1 } }, function(err, post) {
cb( null, post.created_at.getTime() );
});
}
async.parallel({
oldest: getOldest
, newest: getNewest
}
, function( err, results ) {
var days = ( results.newest - results.oldest ) / 1000 / 60 / 60 / 24;
// days = Math.round( days );
cb( null, days );
}
);
}
推荐答案
Mongoose 3.x正在抱怨关于 [> code>调用中的
[]
参数,因为选择字段的参数不再支持数组格式要包含。
Mongoose 3.x is complaining about the []
parameter in your findOne
calls as the array format is no longer supported for the parameter that selects the fields to include.
请尝试使用此代码来查找最新内容:
Try this instead to find the newest:
Tweet.findOne({}, {}, { sort: { 'created_at' : -1 } }, function(err, post) {
console.log( post );
});
将 -1
更改为 1
找到最旧的。
但是因为你没有使用任何字段选择,所以链接一对夫妇更加清晰一起打电话:
But because you're not using any field selection, it's somewhat cleaner to chain a couple calls together:
Tweet.findOne().sort({created_at: -1}).exec(function(err, post) { ... });
甚至将字符串传递给 sort
:
Or even pass a string to sort
:
Tweet.findOne().sort('-created_at').exec(function(err, post) { ... });
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