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Connecting to a database

All Sequel activity begins with connecting to a database, which creates a Sequel::Database object. The Database object is used to create datasets and execute queries. Sequel provides a powerful and flexible mechanism for connecting to databases. There are two main ways to establish database connections:

  1. Using the Sequel.connect method

  2. Using the specialized adapter method (Sequel.sqlite, Sequel.postgres, etc.)

The connection options needed depend on the adapter being used, though most adapters share the same basic connection options.

If you are only connecting to a single database, it is recommended that you store the database object in a constant named DB. This should never be required, but it is the convention that most Sequel code uses.

Using the Sequel.connect method

The connect method usually takes a well-formed URI, which is parsed into connection options needed to open the database connection. The scheme/protocol part of the URI is used to determine the adapter to use:

DB = Sequel.connect('postgres://user:password@localhost/blog') # Uses the postgres adapter

You can use URI query parameters to specify options:

DB = Sequel.connect('postgres://localhost/blog?user=user&password=password')

You can also pass an additional option hash with the connection string:

DB = Sequel.connect('postgres://localhost/blog' :user=>'user', :password=>'password')

You can also just use an options hash without a connection string. If you do this, you must provide the adapter to use:

DB = Sequel.connect(:adapter=>'postgres', :host=>'localhost', :database=>'blog', :user=>'user', :password=>'password')

All of the above statements are equivalent.

Using the specialized adapter method

The specialized adapter method is similar to Sequel.connect with an options hash, except that it automatically populates the :adapter option and assumes the first argument is the :database option, unless the first argument is a hash. So the following statements are equivalent to the previous statements.

DB = Sequel.postgres('blog', :host=>'localhost', :user=>'user', :password=>'password')
DB = Sequel.postgres(:host=>'localhost', :user=>'user', :password=>'password', :database=>'blog')

Note that using an adapter method forces the use of the specified adapter, not a database type, even though some adapters have the same name as the database type. So if you want to connect to SQLite, for example, you can do so using the sqlite, do, jdbc, and swift adapters. If you want to connect to SQLite on JRuby using the jdbc adapter, you should not use Sequel.sqlite for example, as that uses the C-based sqlite3 gem. Instead, the Sequel.jdbc would be appropriate (though as mentioned below, using Sequel.connect is recommended instead of Sequel.jdbc).

Passing a block to either method

Both the Sequel.connect method and the specialized adapter methods take a block. If you provide a block to the method, Sequel will create a Database object and pass it as an argument to the block. When the block returns, Sequel will disconnect the database connection. For example:

Sequel.connect('sqlite://blog.db'){|db| puts db[:users].count}

General connection options

These options are shared by all adapters unless otherwise noted.

:adapter

The adapter to use

:database

The name of the database to which to connect

:default_schema

The database schema to use in schema_modification and introspection.

:host

The hostname of the database server to which to connect

:logger

An array of SQL loggers to log to

:loggers

An array of SQL loggers to log to

:password

The password for the user account

:servers

A hash with symbol keys and hash or proc values, used with master/slave/partitioned database configurations

:single_threaded

Whether to use a single-threaded (non-thread safe) connection pool

:test

Whether to test that a valid database connection can be made (false by default)

:user

The user account name to use logging in

The following options can be specified and are passed to the the database's internal connection pool.

:after_connect

A proc called after a new connection is made, with the connection object (default: nil)

:max_connections

The maximum size of the connection pool (default: 4 connections on most databases)

:pool_sleep_time

The number of seconds to sleep before trying to acquire a connection again (default: 0.001 seconds)

:pool_timeout

The number of seconds to wait if a connection cannot be acquired before raising an error (default: 5 seconds)

Adapter specific connection options

The following sections explain the options and behavior specific to each adapter. If the library the adapter requires is different from the name of the adapter scheme, it is listed specifically, otherwise you can assume that is requires the library with the same name.

ado

Requires: win32ole

The ADO adapter provides connectivity to ADO databases in Windows. It relies on WIN32OLE library, so it isn't usable on other operating systems (except possibly through WINE, but that's fairly unlikely).

The following options are supported:

:command_timeout

Sets the time in seconds to wait while attempting to execute a command before cancelling the attempt and generating an error. Specifically, it sets the ADO CommandTimeout property. If this property is not set, the default of 30 seconds is used.

:driver

The driver to use in the ADO connection string. If not provided, a default of “SQL Server” is used.

:conn_string

The full ADO connection string. If this is provided, the usual options are ignored.

:provider

Sets the Provider of this ADO connection (for example, “SQLOLEDB”). If you don't specify a provider, the default one used by WIN32OLE has major problems, such as creating a new native database connection for every query, which breaks things such as transactions and temporary tables.

Pay special attention to the :provider option, as without specifying a provider, many things will be broken. The SQLNCLI10 provider appears to work well if you are connecting to Microsoft SQL Server, but it is not the default as that would break backwards compatability.

Example connections:

# SQL Server
Sequel.connect('ado:///sequel_test?host=server%5cdb_instance')
Sequel.connect('ado://user:password@server/database?host=server%5cdb_instance&provider=SQLNCLI10')
# Access 2007
Sequel.ado(:conn_string=>'Provider=Microsoft.ACE.OLEDB.12.0;Data Source=drive:\\path\\filename.accdb')
# Access 2000
Sequel.ado(:conn_string=>'Provider=Microsoft.Jet.OLEDB.4.0;Data Source=drive:\\path\\filename.mdb')
# Excel 2000 (for table names, use a dollar after the sheet name, e.g. Sheet1$)
Sequel.ado(:conn_string=>'Provider=Microsoft.Jet.OLEDB.4.0;Data Source=drive:\\path\\filename.xls;Extended Properties=Excel 8.0;')

amalgalite

Amalgalite is an ruby extension that provides self contained access to SQLite, so you don't need to install SQLite separately. As amalgalite is a file backed database, the :host, :user, and :password options are not used.

:database

The name of the database file

:timeout

The busy timeout period given in milliseconds

Without a database argument, assumes a memory database, so you can do:

Sequel.amalgalite

Handles paths in the connection string similar to the SQLite adapter, so see the sqlite section below for details.

cubrid

cubrid is a ruby extension for accessing a CUBRID database. Currently, the ruby cubrid gem is in fairly rough state, with broken transaction support and some other issues, but most things work.

db2

Requires: db2/db2cli

This is the older DB2 adapter. It's recommended you try the ibmdb adapter instead for new DB2 work, as it is better supported.

dbi

Allows access to a multitude of databases via ruby-dbi. Additional options:

:db_type

Specifying 'mssql' allows Microsoft SQL Server specific syntax to be used. Otherwise has no effect.

DBI connection strings are a preprocessed a bit, and are specified with a dbi- in front of the protocol. Examples:

dbi-ado://...
dbi-db2://...
dbi-frontbase://...
dbi-interbase://...
dbi-msql://...
dbi-mysql://...
dbi-odbc://...
dbi-oracle://...
dbi-pg://...
dbi-proxy://...
dbi-sqlite://...
dbi-sqlrelay://...

While the DBI adapter does work, it is recommended that you use another adapter if your database supports it.

do

Requires: data_objects

The DataObjects adapter supports PostgreSQL, MySQL, and SQLite. One possible advantage of using DataObjects is that it does the typecasting in C, which may be faster than the other adapters.

Similar to the JDBC adapter, the DO adapter only cares about connection strings, which can either be the String argument given to Sequel.connect directly or contained in a :uri or :url option. The DO adapter passes through the connection string directly to DataObjects, it does no processing of it (other than removing the do: prefix).

Connection string examples:

do:sqlite3::memory:
do:postgres://user:password@host/database
do:mysql://user:password@host/database

firebird

Requires: fb (using code at github.com/wishdev/fb)

Does not support the :port option.

ibmdb

requires 'ibm_db'

This connects to DB2 using IBM_DB. This is the recommended adapter if you are using a C-based ruby to connect to DB2.

informix

Does not support the :host or :port options. Depending on the configuration of your server it may be necessary to either set

DB.quote_identifier = false

or set

export DELIMIDENT=y

in the scripts environment.

jdbc

Requires: java

Houses Sequel's JDBC support when running on JRuby. Support for individual database types is done using sub adapters. There are currently subadapters for PostgreSQL, MySQL, SQLite, H2, HSQLDB, Derby, Oracle, MSSQL, JTDS, AS400, Progress, Firebird, Informix, and DB2. For PostgreSQL, MySQL, SQLite, H2, Derby, and JTDS, this can use the jdbc-* gem, for the others you need to have the .jar in your CLASSPATH or load the Java class manually before calling Sequel.connect.

You just use the JDBC connection string directly, which can be specified via the string given to Sequel.connect or via the :uri, :url, or :database options. Sequel does no preprocessing of the string, it passes it directly to JDBC. So if you have problems getting a connection string to work, look up the JDBC documentation.

Note that when using a JDBC adapter, the best way to use Sequel is via Sequel.connect, NOT Sequel.jdbc. Use the JDBC connection string when connecting, which will be in a different format than the native connection string. The connection string should start with 'jdbc:'. For PostgreSQL, use 'jdbc:postgresql:', and for SQLite you do not need 2 preceding slashes for the database name (use no preceding slashes for a relative path, and one preceding slash for an absolute path).

Example connection strings:

jdbc:sqlite::memory:
jdbc:postgresql://localhost/database?user=username
jdbc:mysql://localhost/test?user=root&password=root
jdbc:h2:mem:
jdbc:hsqldb:mem:mymemdb
jdbc:derby:memory:myDb;create=true
jdbc:sqlserver://localhost;database=sequel_test;integratedSecurity=true
jdbc:jtds:sqlserver://localhost/sequel_test;user=sequel_test;password=sequel_test
jdbc:oracle:thin:user/password@localhost:1521:database
jdbc:db2://localhost:3700/database:user=user;password=password;
jdbc:firebirdsql:localhost/3050:/path/to/database.fdb
jdbc:jdbcprogress:T:hostname:port:database
jdbc:cubrid:hostname:port:database:::

You can also use JNDI connection strings:

jdbc:jndi:java:comp/env/jndi_resource_name

The following additional options are supported:

:convert_types

If set to false, does not attempt to convert some Java types to ruby types. Setting to false roughly doubles performance when selecting large numbers of rows. Note that you can't provide this option inside the connection string (as that is passed directly to JDBC), you have to pass it as a separate option.

:login_timeout

Set the login timeout on the JDBC connection (in seconds).

mysql

Requires: mysqlplus (or mysql if mysqlplus is not available)

The MySQL adapter does not support the pure-ruby MySQL adapter that used to ship with ActiveRecord, it requires the native adapter.

The following additional options are supported:

:auto_is_null

If set to true, makes “WHERE primary_key IS NULL” select the last inserted id.

:charset

Same as :encoding, :encoding takes precedence.

:compress

Whether to compress data sent/received via the socket connection.

:config_default_group

The default group to read from the in the MySQL config file.

:config_local_infile

If provided, sets the Mysql::OPT_LOCAL_INFILE option on the connection with the given value.

:encoding

Specify the encoding/character set to use for the connection.

:socket

Can be used to specify a Unix socket file to connect to instead of a TCP host and port.

:sql_mode

Set the sql_mode(s) for a given connection. Can be single symbol or string, or an array of symbols or strings (e.g. :sql_mode=>[:no_zero_date, :pipes_as_concat]).

:timeout

Sets the wait_timeout for the connection, defaults to 1 month.

:read_timeout

Set the timeout in seconds for reading back results to a query.

:connect_timeout

Set the timeout in seconds before a connection attempt is abandoned.

mysql2

This is a newer MySQL adapter that does typecasting in C, so it is often faster than the mysql adapter. Supports the same additional options as the mysql adapter, except for :compress, and uses :timeout instead of :read_timeout and :connect_timeout.

odbc

The ODBC adapter allows you to connect to any database with the appropriate ODBC drivers installed. The :database option given ODBC database should be the DSN (Descriptive Service Name) from the ODBC configuration.

Sequel.odbc('mydb', :user => "user", :password => "password")

The :host and :port options are not respected. The following additional options are supported:

:db_type

Can be specified as 'mssql' or 'progress' to use SQL syntax specific to those databases.

:driver

The name of the ODBC driver to utilize.

openbase

The :port option is ignored.

oracle

Requires: oci8

The following additional options are supported:

:autosequence

Set to true to use Sequel's conventions to guess the sequence to use for datasets. False by default.

:prefetch_rows

The number of rows to prefetch. Defaults to 100, a larger number can be specified and may improve performance when retrieving a large number of rows.

:privilege

The Oracle privilege level.

postgres

Requires: pg (or postgres if pg is not available)

The Sequel postgres adapter works with the pg, postgres, and postgres-pr ruby libraries. The pg library is the best supported, as it supports real bound variables and prepared statements. If the pg library is being used, Sequel will also attempt to load the sequel_pg library, which is a C extension that optimizes performance when Sequel is used with pg. All users of Sequel who use pg are encouraged to install sequel_pg.

The following additional options are supported:

:charset

Same as :encoding, :encoding takes precedence

:encoding

Set the client_encoding to the given string

:connect_timeout

Set the number of seconds to wait for a connection (default 20, only respected if using the pg library).

:sslmode

Set to 'disable', 'allow', 'prefer', 'require' to choose how to treat SSL (only respected if using the pg library)

sqlite

Requires: sqlite3

As SQLite is a file-based database, the :host and :port options are ignored, and the :database option should be a path to the file.

Examples:

# In Memory databases:
Sequel.sqlite
Sequel.connect('sqlite:/') 
Sequel.sqlite(':memory:')

# Relative Path
Sequel.sqlite('blog.db')
Sequel.sqlite('./blog.db')
Sequel.connect('sqlite://blog.db')

# Absolute Path
Sequel.sqlite('/var/sqlite/blog.db')
Sequel.connect('sqlite:///var/sqlite/blog.db')

The following additional options are supported:

:timeout

the busy timeout to use in milliseconds (default: 5000).

swift

swift is a ruby 1.9 only library, so you'll need to be running ruby 1.9. It can connect to SQLite, MySQL, and PostgreSQL, and you must specify which database using the db_type option.

You need to install one of the swift db adapters

  • swift-db-sqlite3

  • swift-db-mysql

  • swift-db-postgres

Examples:

swift:///?database=:memory:&db_type=sqlite
swift://root:root@localhost/test?db_type=mysql
swift://root:root@localhost/test?db_type=postgres

tinytds

Requires: tiny_tds

Because the underscore is not a valid character in a URI schema, the adapter is named tinytds instead of tiny_tds. The connection options are passed directly to tiny_tds, except that the tiny_tds :username option is set to the Sequel :user option. If you want to use an entry in the freetds.conf file, you should specify the :dataserver option with that name as the value. Some other options that you may want to set are :login_timeout, :timeout, :tds_version, :azure, :appname, and :encoding, see the tiny_tds README for details.

Other Sequel specific options:

:textsize

Override the default TEXTSIZE setting for this connection. The FreeTDS default is small (around 64000 bytes), but can be set up to around 2GB. This should be specified as an integer. If you plan on setting large text or blob values via tinytds, you should use this option or modify your freetds.conf file.

For highest performance, you should disable any identifier output method when using the tinytds adapter, which probably means disabling any identifier input method as well. The default for Microsoft SQL Server is to :downcase identifiers on output and :upcase them on input, so the highest performance will require changing the setting from the default.

The Sequel tinytds adapter requires tiny_tds >= 0.4.5, and if you are using FreeTDS 0.91, you must at least be using 0.91rc2 (0.91rc1 does not work).

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