About the array of MongoDB arrays Group array

MongoDB supports array type

MongoDB is really good at the function of the group. For complex data processing with mapreduce, but this thing is very slow, more suitable for script processing data, not suitable for real-time data query

In the field of real-time data processing to use pipelines, about the pipeline syntax, see:

http://blog.csdn.net/terry_water/article/details/43529367

If $class_artist is an array, you need to group the data inside the arrays, then you can use $unwind

, its function is to split the array, forming a number of data.

Db.articles.aggregate ([  {$match: {class_date: {$gte: Date}}},  {$project: {_id:0, class_artist:1}},  { $unwind: "$class _artist"},  {$group: {_id: "$class _artist", Tags: {$sum: 1}}},  {$project: {_id:0,class_artis T: "$_id", Tags:1}},  {$sort: {tags:-1}}])

In the YII2 framework:

You can add a function to the query.php:

Splits the $filter _size array, and then group.

Public Function filtersize ($db = null) {$collection = $this->getcollection ($db);        $pipelines = [];        if ($this->where!== null) {            $pipelines [] = ['? match ' = $collection->buildcondition ($this->where)];        } $pipelines [] = ['? unwind ' = "\ $filter _size"];        $pipelines [] = [            ' $group ' + = [                ' _id ' + ' \ $filter _size ', ' num_total ' and ' = '                    sum ' = 1,                ] ,            ]        ]; $pipelines [] = ['? sort '] = [' _id ' = 1]];        $result = $collection->aggregate ($pipelines); return $result;       }

About the array of MongoDB arrays Group array