Package com.mongodb

Class DB

java.lang.Object

com.mongodb.DB

@ThreadSafe
public class DB
extends Object

A thread-safe client view of a logical database in a MongoDB cluster. A DB instance can be achieved from a MongoClient instance using code like:

 
 MongoClient mongoClient = new MongoClient();
 DB db = mongoClient.getDB("<db name>");
 
 

See MongoClient.getDB(String) for further information about the effective deprecation of this class.

See Also:

MongoClient

MongoDB documentation

Database

Method Summary

Modifier and Type	Method	Description
boolean	collectionExists(String collectionName)	Checks to see if a collection with a given name exists on a server.
CommandResult	command(DBObject command)	Executes a database command.
CommandResult	command(DBObject command, DBEncoder encoder)	Executes a database command.
CommandResult	command(DBObject command, ReadPreference readPreference)	Executes the command against the database with the given read preference.
CommandResult	command(DBObject command, ReadPreference readPreference, DBEncoder encoder)	Executes a database command with the selected readPreference, and encodes the command using the given encoder.
CommandResult	command(String command)	Executes a database command.
CommandResult	command(String command, ReadPreference readPreference)	Executes a database command.
DBCollection	createCollection(String collectionName, DBObject options)	Creates a collection with a given name and options.
DBCollection	createView(String viewName, String viewOn, List<? extends DBObject> pipeline)	Creates a view with the given name, backing collection/view name, and aggregation pipeline that defines the view.
DBCollection	createView(String viewName, String viewOn, List<? extends DBObject> pipeline, DBCreateViewOptions options)	Creates a view with the given name, backing collection/view name, aggregation pipeline, and options that defines the view.
void	dropDatabase()	Drops this database.
DBCollection	getCollection(String name)	Gets a collection with a given name.
Set<String>	getCollectionNames()	Returns a set containing the names of all collections in this database.
MongoClient	getMongoClient()	Gets the MongoClient instance
String	getName()	Returns the name of this database.
ReadConcern	getReadConcern()	Get the read concern for this database.
ReadPreference	getReadPreference()	Gets the read preference for this database.
DB	getSisterDB(String name)	Gets another database on same server
WriteConcern	getWriteConcern()	Gets the write concern for this database.
void	setReadConcern(ReadConcern readConcern)	Sets the read concern for this database.
void	setReadPreference(ReadPreference readPreference)	Sets the read preference for this database.
void	setWriteConcern(WriteConcern writeConcern)	Sets the write concern for this database.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Detail

getMongoClient

public MongoClient getMongoClient()

Gets the MongoClient instance

Returns:

the MongoClient instance that this database was constructed from

Throws:

IllegalStateException - if this DB was not created from a MongoClient instance

Since:

3.9

setReadPreference

public void setReadPreference(ReadPreference readPreference)

Sets the read preference for this database. Will be used as default for read operations from any collection in this database. See the documentation for ReadPreference for more information.

Parameters:

readPreference - ReadPreference to use

MongoDB documentation

Read Preference

setWriteConcern

public void setWriteConcern(WriteConcern writeConcern)

Sets the write concern for this database. It will be used for write operations to any collection in this database. See the documentation for WriteConcern for more information.

Parameters:

writeConcern - WriteConcern to use

MongoDB documentation

Write Concern

getReadPreference

public ReadPreference getReadPreference()

Gets the read preference for this database.

Returns:

ReadPreference to be used for read operations, if not specified explicitly

MongoDB documentation

Read Preference

getWriteConcern

public WriteConcern getWriteConcern()

Gets the write concern for this database.

Returns:

WriteConcern to be used for write operations, if not specified explicitly

MongoDB documentation

Write Concern

setReadConcern

public void setReadConcern(ReadConcern readConcern)

Sets the read concern for this database.

Parameters:

readConcern - the read concern to use for this collection

Since:

3.3

MongoDB documentation

Read Concern

Since server release

3.2

getReadConcern

public ReadConcern getReadConcern()

Get the read concern for this database.

Returns:

the ReadConcern

Since:

3.3

MongoDB documentation

Read Concern

Since server release

3.2

getCollection

public DBCollection getCollection(String name)

Gets a collection with a given name.

Parameters:

name - the name of the collection to return

Returns:

the collection

Throws:

IllegalArgumentException - if the name is invalid

See Also:

MongoNamespace.checkCollectionNameValidity(String)

dropDatabase

public void dropDatabase()

Drops this database. Removes all data on disk. Use with caution.

Throws:

MongoException - if the operation failed

MongoDB documentation

Drop Database

getName

public String getName()

Returns the name of this database.

Returns:

the name

getCollectionNames

public Set<String> getCollectionNames()

Returns a set containing the names of all collections in this database.

Returns:

the names of collections in this database

Throws:

MongoException - if the operation failed

MongoDB documentation

getCollectionNames()

createCollection

public DBCollection createCollection(String collectionName,
                                     @Nullable
                                     DBObject options)

Creates a collection with a given name and options. If the collection already exists, this throws a CommandFailureException.

Possible options:

• capped (boolean) - Enables a collection cap. False by default. If enabled, you must specify a size parameter.
• size (int) - If capped is true, size specifies a maximum size in bytes for the capped collection. When capped is false, you may use size to preallocate space.
• max (int) - Optional. Specifies a maximum "cap" in number of documents for capped collections. You must also specify size when specifying max.

Note that if the options parameter is null, the creation will be deferred to when the collection is written to.

Parameters:

collectionName - the name of the collection to return

options - options

Returns:

the collection

Throws:

MongoCommandException - if the server is unable to create the collection

WriteConcernException - if the WriteConcern specified on this DB could not be satisfied

MongoException - for all other failures

MongoDB documentation

createCollection()

createView

public DBCollection createView(String viewName,
                               String viewOn,
                               List<? extends DBObject> pipeline)

Creates a view with the given name, backing collection/view name, and aggregation pipeline that defines the view.

Parameters:

viewName - the name of the view to create

viewOn - the backing collection/view for the view

pipeline - the pipeline that defines the view

Returns:

the view as a DBCollection

Throws:

MongoCommandException - if the server is unable to create the collection

WriteConcernException - if the WriteConcern specified on this DB could not be satisfied

MongoException - for all other failures

Since:

3.4

MongoDB documentation

Create Command

Since server release

3.4

createView

public DBCollection createView(String viewName,
                               String viewOn,
                               List<? extends DBObject> pipeline,
                               DBCreateViewOptions options)

Creates a view with the given name, backing collection/view name, aggregation pipeline, and options that defines the view.

Parameters:

viewName - the name of the view to create

viewOn - the backing collection/view for the view

pipeline - the pipeline that defines the view

options - the options for creating the view

Returns:

the view as a DBCollection

Throws:

MongoCommandException - if the server is unable to create the collection

WriteConcernException - if the WriteConcern specified on this DB could not be satisfied

MongoException - for all other failures

Since:

3.4

MongoDB documentation

Create Command

Since server release

3.4

command

public CommandResult command(String command)

Executes a database command. This method constructs a simple DBObject using command as the field name and true as its value, and calls command(DBObject, ReadPreference) with the default read preference for the database.

Parameters:

command - command to execute

Returns:

result of command from the database

Throws:

MongoException - if the command failed

MongoDB documentation

Commands

command

public CommandResult command(DBObject command)

Executes a database command. This method calls command(DBObject, ReadPreference) with the default read preference for the database.

Parameters:

command - DBObject representation of the command to be executed

Returns:

result of the command execution

Throws:

MongoException - if the command failed

MongoDB documentation

Commands

command

public CommandResult command(DBObject command,
                             DBEncoder encoder)

Executes a database command. This method calls command(DBObject, ReadPreference, DBEncoder) with the default read preference for the database.

Parameters:

command - DBObject representation of the command to be executed

encoder - DBEncoder to be used for command encoding

Returns:

result of the command execution

Throws:

MongoException - if the command failed

MongoDB documentation

Commands

command

public CommandResult command(DBObject command,
                             ReadPreference readPreference,
                             @Nullable
                             DBEncoder encoder)

Executes a database command with the selected readPreference, and encodes the command using the given encoder.

Parameters:

command - The DBObject representation the command to be executed

readPreference - Where to execute the command - this will only be applied for a subset of commands

encoder - The DBEncoder that knows how to serialise the command

Returns:

The result of executing the command, success or failure

Since:

2.12

MongoDB documentation

Commands

command

public CommandResult command(DBObject command,
                             ReadPreference readPreference)

Executes the command against the database with the given read preference.

Parameters:

command - The DBObject representation the command to be executed

readPreference - Where to execute the command - this will only be applied for a subset of commands

Returns:

The result of executing the command, success or failure

Since:

2.12

MongoDB documentation

Commands

command

public CommandResult command(String command,
                             ReadPreference readPreference)

Executes a database command. This method constructs a simple DBObject and calls command(DBObject, ReadPreference).

Parameters:

command - The name of the command to be executed

readPreference - Where to execute the command - this will only be applied for a subset of commands

Returns:

The result of the command execution

Throws:

MongoException - if the command failed

Since:

2.12

MongoDB documentation

Commands

getSisterDB

public DB getSisterDB(String name)

Gets another database on same server

Parameters:

name - name of the database

Returns:

the DB for the given name

collectionExists

public boolean collectionExists(String collectionName)

Checks to see if a collection with a given name exists on a server.

Parameters:

collectionName - a name of the collection to test for existence

Returns:

false if no collection by that name exists, true if a match to an existing collection was found

Throws:

MongoException - if the operation failed

toString

public String toString()

Overrides:

toString in class Object