# basic search

```javascript
db.getCollection('collection_1').find({});
```

# projection

```javascript
db.getCollection('collection_1').find({}, {'_id': 1});
```

# limit

```javascript
db.getCollection('collection_1').find({}, {'_id': 1}).limit(10);
```

# count

```javascript
db.getCollection('collection_1').find({}).count();
```

# remove

```javascript
db.getCollection('collection_1').remove({'_id': ObjectId('xxxxxxxxxx')});
```

# pattern search

```javascript
db.getCollection('collection_1').find({'field_1': {'$regex': 'pattern'}})
db.getCollection('collection_1').find({'field_1': {'$regex': 'pattern', '$options': 'i'}})
```

# time search

```javascript
function objectIdWithTimestamp(timestamp) {
    // Convert string date to Date object (otherwise assume timestamp is a date)
    if (typeof(timestamp) == 'string') {
        timestamp = new Date(timestamp);
    }

    // Convert date object to hex seconds since Unix epoch
    var hexSeconds = Math.floor(timestamp/1000).toString(16);

    // Create an ObjectId with that hex timestamp
    var constructedObjectId = ObjectId(hexSeconds + "0000000000000000");

    return constructedObjectId
}

db.getCollection('collection_1').find({'_id': {$gt: objectIdWithTimestamp('2017/11/04')}});
```

# filter elements where field_1 exists

```javascript
db.getCollection('collection_1').find({'field_1': {'$exists': 1}})
```

# filter elements if field in or not in list

```javascript
db.getCollection('collection_1').find({'field_1': {'$in': []}})
db.getCollection('collection_1').find({'field_1': {'$nin': []}})
db.getCollection('collection_1').find({'_id': {'$in': [ObjectId('xxxxxxxxxx'), ObjectId('xxxxxxxxxx') ]}})
```

# group by

```javascript
db.getCollection('collection_1').remove({'_id': ObjectId('xxxxxxxxxx')});
```

# group by advanced example

```javascript
db.getCollection('collection_1').aggregate([
    {'$unwind': '$field_1'},
    {'$unwind': '$field_1.sub_field_1'},
    {'$project': {'new_field_1_name': '$field_1.sub_field_1', '_id': 1}},
    {'$group': { _id: null, count: {'$sum': 1}}}
])
```

# copy elements to another collection

```javascript
db.getCollection('collection_1').find().forEach(function(doc){
    db.getCollection('collection_2').insert(doc);
});
```