MongoDB

Documented oriented database. A database might have several collections and each collection doesn't enforce a schema for the documents stored in it.

FerretDB

https://docs.ferretdb.io/

FerretDB is an open-source alternative to MongoDB. It is a proxy that converts MongoDB 5.0+ wire protocol queries to SQL and uses PostgreSQL with DocumentDB extension as a database engine. FerretDB is compatible with MongoDB drivers and can be used as a direct replacement for MongoDB 5.0+.

MongoDB has SSPL licensing issues.

Query by data type

Select all documents in the inventory collection where the price field value is a Double.

   1 db.inventory.find( { price: { $type : 1 } } )

Select all documents in the inventory collection where the datex field value is a Date.

   1 db.inventory.find( { datex: { $type : 9 } } )

Data types

Type	Number
Double	1
String	2
Object	3
Array	4
Binary data	5
Undefined (deprecated)	6
Object id	7
Boolean	8
Date	9
Null	10
Regular Expression	11
JavaScript	13
Symbol	14
JavaScript (with scope)	15
32-bit integer	16
Timestamp	17
64-bit integer	18
Min key	255
Max key	127

PHP driver

Manual install

cd /tmp
wget http://pecl.php.net/get/mongo-1.4.3.tgz
tar xvzf mongo-1.4.3.tgz
yum install php-devel #on CentOS
phpize
./configure
make
make install
add extension=mongo.so to /etc/php.ini
In CentOS 64 bit the mongo.so should be located in /usr/lib64/php/modules/mongo.so

Aggregation examples

http://docs.mongodb.org/manual/reference/sql-aggregation-comparison/

Example 1

   1 SELECT country,city,min(timestampx) as minx,max(timestampx) as maxx,count(*) as countx
   2 FROM collx 
   3 GROUP BY country,city 
   4 WHERE idxyz=1234 AND timestampx>='2011-06-04T00:00:00' AND timestampx<='2012-12-04T23:59:59'
   5 ORDER BY minx

   1 db.collx.runCommand( 
   2   {  "aggregate":"collx" , "pipeline":[
   3       {"$match": 
   4          {
   5            idxyz:1234 , 
   6            "timestampx":{ 
   7              "$gte":ISODate("2011-06-04T00:00:00") , 
   8              "$lte":ISODate("2012-12-04T23:59:59") 
   9            }   
  10          } 
  11       } 
  12       ,
  13       {"$group": 
  14          {
  15            "_id":  {"country":"$country","city":"$city"} , 
  16            "minx":{"$min":"$timestampx"} , 
  17            "maxx":{"$max":"$timestampx"} ,  
  18            "countx":{"$sum":1}  
  19          }    
  20       }
  21       ,
  22       {
  23         "$sort":
  24         { 
  25           "minx":1
  26         } 
  27       } 
  28     ]       
  29   }   
  30 )

   1 db.collx.aggregate( 
   2      [
   3       {"$match": 
   4          {
   5            idxyz:1234 , 
   6            "timestampx":{ 
   7              "$gte":ISODate("2011-06-04T00:00:00") , 
   8              "$lte":ISODate("2012-12-04T23:59:59") 
   9            }   
  10          } 
  11       } 
  12       ,
  13       {"$group": 
  14          {
  15            "_id":  {"country":"$country","city":"$city"} , 
  16            "minx":{"$min":"$timestampx"} , 
  17            "maxx":{"$max":"$timestampx"} ,  
  18            "countx":{"$sum":1}  
  19          }    
  20       }
  21       ,
  22       {
  23         "$sort":
  24         { 
  25           "minx":1
  26         } 
  27       } 
  28     ]       
  29 )

   1 db.collx.runCommand(  { "aggregate":"collx" , "pipeline":[
   2       {"$group": { "_id":  {"fld":"$fldx"} , "countx":{"$sum":1}  }   }
   3       ,
   4       { "$sort": { "countx":1  } } 
   5 ] } ).result

Get creation timestamp from document

Inside the creation timestamp is stored in the _id field .

Using the method getTimestamp on an ObjectiId, is possible to get the creation timestamp.

   1 // runned inside mongo shell
   2 ObjectId("52840c4facb4f200d8a6518a").getTimestamp()
   3 // returned ISODate("2013-11-13T23:33:35Z")
   4

Update field on document

   1 db.products.update( 
   2 { sku: "abc123" },
   3 { $set: { quantity: 500,  instock: true  }    }
   4 )

Find documents that don't have a field

   1 db.products.find( { fieldx:{$exists:false} } )

Find docs with status equal Failure and only show the _id and status fields

   1 db.products.find( {status:"Failure"} , { status:1  } )

Set journal small

   1 # smallfiles=true to the config file /etc/mongodb.conf.
   2 service mongodb stop
   3 cd /var/lib/mongodb/journal
   4 rm *
   5 service mongodb start
   6 mongo

Sort by field

descending
- db.rxtx.find().sort({timestamp:0}).limit(10)
ascending
- db.rxtx.find().sort({timestamp:1}).limit(10)