mongodb_lookup_query.js

db.influencers.aggregate([
{
    $match: {ac: 1}
},
{
    $project: {_id: 1}
},
{  
    $lookup: {
        from: 'media',        
        let: {in_id: '$_id'},
        pipeline: [
            {
                $match: {
                    $expr: {
                        $eq: ['$i_id', '$$in_id']
                    }
                }
            }
            
        ],
        as: 'media'
    }
},
    {
        $match: {media: {$ne: []}}
    },
    {
        $unwind: '$media'
    },
    {
        $limit: 20
    }
])