MongoDB Common directives

• db
  View the database for the current operation

• show dbs
  Show all databases

• show collections
  Displays all collections under the current database

• use database_name
  Connect to a database named "database_name" and create if it does not exist

• db.dropDatabase()
  Delete current Database

• db.collection_name.drop()
  Delete named "Collection_name" collection

• db.createCollection(‘collection_name‘ , {capped : true ,size : 100000} )
  Create a collection called "collection_name", specifying a length of 100000b

• db.collection_name.find({})
  The query is called "collection_name" in the collection of all documents, curly braces for the query criteria, unconditional query all.

• db.collection_name.find({}).pretty()
  Query all the documents in the collection, pretty to beautify the display effect.

• db.collection_name.find({}).limit(1).skip(2)
  Pagination Displays the result of the query, limit is the starting position, and skip is the number of bars taken.

• db.collection_name.find({}).sort({KEY:1})
  Sort for sorting criteria, 1 for ascending, 1 for descending

• db.collection_name.insert({‘name‘:‘yan‘})
  Inserts a document into the collection "collection_name".

• ' Db.collection_name.save ({}) '
  Save the data, and if you do not specify an ID, the effect is the same as insert, which is the updated action if the ID is specified.

• db.collection_name.update({<query>,<update>,{upsert:<boolean>,multi:<boolean>,writeConcern:<document>}})
  Update document
  • Query: Search criteria
  • Update: Fields that need to be updated
  • Upsert: Optional (false by default), set to true: Inserts are made if there are no documents that meet the criteria of the query.
  • Multi: Optional (false by default), set to true: if there are more than one document that meets the query criteria, all of the documents are updated. Set false: Updates only the first document to the query.
  • Writeconcern: Optional, throws an exception level

• db.collection_name.remove(<query>,{justOne:<boolean>,writeConcern:<document>})
  Delete

• db.collection_name.ensureIndex({KEY:1})
  Index, can write multiple (composite index)

• db.collection.aggregate( [ $group : { _id : ‘$__xh‘ , num_tutorial : {$sum : 1} } ] )
  Aggregation, which is an advanced query, for example, the total number of statistical classes

MongoDB Common directives