[英]MongoDB with Mongoose - Find only certain child documents
MongoDB 3.0.7 and Mongoose 4.3.4. MongoDB 3.0.7和Mongoose 4.3.4。
Schema: 架构:
var schema = new mongoose.Schema({
confirmed: { type: Boolean, default: false },
moves: [new mongoose.Schema({
name: { type: String, default: '' },
live: { type: Boolean, default: true }
})]
});
mongoose.model('Batches', schema);
Query: 查询:
var Batch = mongoose.model('Batches');
var query = {
confirmed: true,
moves: {
$elemMatch: {
live: true
}
}
};
Batch.find(query).exec(function(err, batches){
console.log('batches: ', batches);
});
I need to return all batches that are confirmed
, and all moves within the returned batches that are live
. 我需要返回所有已confirmed
批次,以及返回的live
批次中的所有移动。
At the moment, the above is returning only the confirmed
batches (which is what I want), but all the moves
in each returned batch (which is not what I want). 目前,以上仅返回已confirmed
批次(这是我想要的),但是每个返回的批次中的所有 moves
(这都不是我想要的)。 So the limiting of moves by the live
flag is not working. 因此,通过live
标志限制移动不起作用。
How do I limit the sub-documents that are returned..? 如何限制返回的子文档?
Ideally, I would like to keep everything that controls the data returned within query
passed to find
, and not have to call more methods on Batch
. 理想情况下,我想保留所有控制传递给find
query
返回的数据的控件,而不必在Batch
上调用更多方法。
For Mongoose versions >=4.3.0
which support MongoDB Server 3.2.x
, you can use the $filter
operator with the aggregation framework to limit/select the subset of the moves array to return based on the specified condition. 对于支持MongoDB Server 3.2.x
Mongoose版本>=4.3.0
,可以将$filter
运算符与聚合框架一起使用,以根据指定条件限制/选择要返回的moves数组的子集。 This returns an array with only those elements that match the condition, so you will use it in the $project
stage to modify the moves array based on the filter above. 这将返回仅包含与条件匹配的那些元素的数组,因此您将在$project
阶段中使用它来基于上面的过滤器修改moves数组。
The following example shows how you can go about this: 以下示例显示了如何执行此操作:
var Batch = mongoose.model('Batches'),
pipeline = [
{
"$match": { "confirmed": true, "moves.live": true }
},
{
"$project": {
"confirmed": 1,
"moves": {
"$filter": {
"input": "$moves",
"as": "el",
"cond": { "$eq": [ "$$el.live", true ] }
}
}
}
}
];
Batch.aggregate(pipeline).exec(function(err, batches){
console.log('batches: ', batches);
});
or with the fluent aggregate()
API pipeline builder: 或使用流畅的aggregate()
API管道构建器:
Batch.aggregate()
.match({
"$match": { "confirmed": true, "moves.live": true }
})
.project({
"confirmed": 1,
"moves": {
"$filter": {
"input": "$moves",
"as": "el",
"cond": { "$eq": [ "$$el.live", true ] }
}
}
})
.exec(function(err, batches){
console.log('batches: ', batches);
});
For Mongoose versions ~3.8.8, ~3.8.22, 4.x
which support MongoDB Server >=2.6.x
, you could filter out the false values using a combination of the $map
and $setDifference
operators: 对于支持MongoDB Server >=2.6.x
Mongoose版本~3.8.8, ~3.8.22, 4.x
您可以使用$map
和$setDifference
运算符的组合来滤除错误值:
var Batch = mongoose.model('Batches'),
pipeline = [
{
"$match": { "confirmed": true, "moves.live": true }
},
{
"$project": {
"confirmed": 1,
"moves": {
"$setDifference": [
{
"$map": {
"input": "$moves",
"as": "el",
"in": {
"$cond": [
{ "$eq": [ "$$el.live", true ] },
"$$el",
false
]
}
}
},
[false]
]
}
}
}
];
Batch.aggregate(pipeline).exec(function(err, batches){
console.log('batches: ', batches);
});
You can use the aggregation framework's $unwind
method to split them into separate documents, here are sample codes. 您可以使用聚合框架的$unwind
方法将它们拆分为单独的文档,这里是示例代码。
Batches.aggregate(
{ $match: {'confirmed': true, 'moves.live': true}},
{$unwind: '$moves'},
{$project: {
confirmed: 1
name: '$moves.name',
live:'$moves.live'
}
}, function(err, ret){
})
The query does not limit moves by the live flag. 该查询不通过实时标志来限制移动。 The query reads: find all confirmed batches with at least one live move . 该查询显示: 查找所有已确认批次且至少进行一次实时移动 。
There are 2 options to retrieve live moves only: retrieve all moves, and filter the array clientside; 有2个选项只能检索实时移动:检索所有移动,并过滤客户端数组; or map-reduce it serverside - unwind all moves, filter live ones, and group by document id. 或在服务器端缩小地图大小 -展开所有移动,过滤实时移动并按文档ID分组。
The former is simpler to implement, but will result with more data transfer, cpu and memory consumption on the client side. 前者易于实现,但会导致客户端的数据传输,CPU和内存消耗更多。 The later is more efficient, but a bit more complex to implement - if you expect more than 16Mb in the response, you will need to use a temporary collection. 后者效率更高,但实现起来却有些复杂-如果您希望响应中的数据超过16Mb,则需要使用一个临时集合。
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