mongoengine聚合函数

用法

pipeline = []
res = db.col.aggregate(pipeline)   # 返回cursor
res = model.objects.aggregate(pipeline)
print(list(res))

$match

{ $match: { $expr: { } } }

# 简单相等查询
{'$match': {'name': 'zoro'}}
# AND 查询
{'$match': {'name': 'zoro', 'age': 20}}
# OR 查询
{'$match':
  {
    '$or': [
          { 'score': { '$gt': 70, '$lt': 90 } },
          { 'views': { '$gte': 1000 } }
    ]
  }
}

$sort

{ $sort: { : , : … } }

# 正序
{'$sort': {'name': 1}}
# 逆序
{'$sort': {'name': -1}}
# 多列
{'$sort': {'name': 1, 'age': -1}}

$facet, $skip, $limit, $count

{
    '$facet': {
        'data': [{'$skip': (page - 1) * pageSize}, {'$limit': pageSize}],
        'total': [
            {'$count': 'count'}
        ],
    }
}

$group

{
    '$group': {
        '_id': {'name': '$name', 'age': '$age'}
    }
}

$match + $group + $sort + $facet

查询 + 去重 + 排序 + 分页

pipeline = [
    {
        '$match': {'Species': 'NDM8'}
    },
    {
        '$group': {'_id': {'Species': '$Species', 'Map_ID': '$Map_ID'}}
    },
    {
        '$sort': {'_id.Map_ID': -1}
    },
    {
        '$facet': {
            'data': [{'$skip': 20}, {'$limit': 10}],
            'total': {'$count': 'count'}
        },
    }
]

[
    {
        'data': [
            {'_id': {'Species': 'NDM8', 'Map_ID': 'map00061'}},
            {'_id': {'Species': 'Pima90', 'Map_ID': 'map00061'}},
            {'_id': {'Species': 'Pima90', 'Map_ID': 'map00073'}}], 
        'total': [{'count': 512}]
    }
]

$unwind

将指定的Array列展开为多行

{
  $unwind: '$fieldName',
}

• https://stackoverflow.com/questions/29278962/sort-and-group-in-one-mongodb-aggregation-query