[英]NodeJs: Filter mongo query results with results from another collection
I have a situation where I need to perform logic on a distinct set of values from a mongo collection (A) and then save result to another collection (B). 我遇到一种情况,需要对mongo集合(A)的一组不同值执行逻辑,然后将结果保存到另一个集合(B)。 However the contents of (A) will change over time and so I only want to perform the logic on those documents in (A) where there is not a corresponding document in (B).
但是(A)的内容会随着时间而变化,因此我只想对(B)中没有相应文档的(A)中的那些文档执行逻辑。 As joins aren't supported, I am trying to do this at the Node level.
由于不支持联接,因此我尝试在节点级别执行此操作。 I am querying all items in collection (A) and using
findOne
to look for the corresponding entry in collection (B). 我正在查询集合(A)中的所有项目,并使用
findOne
在集合(B)中查找相应的条目。 If I find it, I would like to remove it from the array, but I am stuck because findOne
uses an asynchronous callback which doesn't seem to work with the array filter
method. 如果找到它,我想将其从数组中删除,但是我被卡住了,因为
findOne
使用了异步回调,该回调似乎不适用于数组filter
方法。 Is there a better way to do this: 有一个更好的方法吗:
function loadNewDocumentsFromDB(callback){
db.collection('A', function(err, acollection){
bcollection.find().toArray(function(err, arr){
if(arr){
// toQuery is the global array to be used elsewhere
toQuery = arr.map(function(config){
transformed =
{
args: config._id, // these args are a doc representing a unique entry in 'B'
listings: config.value.id.split(',') // used by other functions
};
return transformed;
})
.filter(function(transformed){
db.collection('B', function(err, bcollection){
bcollection.findOne(transformed.args, function(err, doc){
// I want these values returned from the filter function not the callback
if(doc){
return false; // want to remove this from list of toQuery
}else{
return true; // want to keep in my list
});
});
}
callback();
});
});
}
This was how I managed to get it working: 这就是我设法使其工作的方式:
function loadOptionsFromDB(callback){
toQuery = [];
db.collection('list', function(err, list){
db.collection('data', function(err, data){
list.find().each(function(err, doc){
if(doc){
transformed =
{
args: doc._id,
listings: doc.value.id.split(',')
};
(function(obj){
data.findOne(obj.args, function(err, found){
if(found){}
else{
toQuery.push(obj);
}
});
})(transformed);
}else{
//Done finding
setTimeout(callback, 20000);
}
});
});
});
}
A better way would be to do this on the database. 更好的方法是在数据库上执行此操作。 Check if 2 executions of http://docs.mongodb.org/manual/core/map-reduce/ would be of any use to you.
检查是否有两次执行http://docs.mongodb.org/manual/core/map-reduce/对您有用。 See Merging two collections in MongoDB for more information
有关更多信息,请参见在MongoDB中合并两个集合。
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