Sequel::Schema::AlterTableGenerator

Schema::AlterTableGenerator is an internal class that the user is not expected to instantiate directly. Instances are created by Database#alter_table. It is used to specify table alteration parameters. It takes a Database object and a block of operations to perform on the table, and gives the Database an array of table altering operations, which the database uses to alter a table’s description.

For more information on Sequel’s support for schema modification, see the “Schema Modification” guide.

Methods

Public Class

new

Public Instance

add_column
add_constraint
add_foreign_key
add_full_text_index
add_index
add_primary_key
add_spatial_index
add_unique_constraint
drop_column
drop_constraint
drop_foreign_key
drop_index
operations
rename_column
set_column_allow_null
set_column_default
set_column_not_null
set_column_type

Attributes

[R]

An array of operations to perform

Public Class methods

new(db, &block)

Set the Database object to which to apply the changes, and evaluate the block in the context of this object.

    # File lib/sequel/database/schema_generator.rb
433 def initialize(db, &block)
434   @db = db
435   @operations = []
436   instance_exec(&block) if block
437 end

Public Instance methods

add_column(name, type, opts = OPTS)

Add a column with the given name, type, and opts. See CreateTableGenerator#column for the available options.

add_column(:name, String) # ADD COLUMN name varchar(255)

PostgreSQL specific options:

:if_not_exists

Set to true to not add the column if it already exists (PostgreSQL 9.6+)

MySQL specific options:

:after	The name of an existing column that the new column should be positioned after
:first	Create this new column before all other existing columns

    # File lib/sequel/database/schema_generator.rb
452 def add_column(name, type, opts = OPTS)
453   op = {:op => :add_column, :name => name, :type => type}.merge!(opts)
454   index_opts = op.delete(:index)
455   @operations << op
456   add_index(name, index_opts.is_a?(Hash) ? index_opts : OPTS) if index_opts
457   nil
458 end

add_constraint(name, *args, &block)

Add a constraint with the given name and args. See CreateTableGenerator#constraint.

add_constraint(:valid_name, Sequel.like(:name, 'A%'))
# ADD CONSTRAINT valid_name CHECK (name LIKE 'A%' ESCAPE '\')
add_constraint({name: :valid_name, deferrable: true}, Sequel.like(:name, 'A%'))
# ADD CONSTRAINT valid_name CHECK (name LIKE 'A%' ESCAPE '\') DEFERRABLE INITIALLY DEFERRED

    # File lib/sequel/database/schema_generator.rb
467 def add_constraint(name, *args, &block)
468   opts = name.is_a?(Hash) ? name : {:name=>name}
469   @operations << opts.merge(:op=>:add_constraint, :type=>:check, :check=>block || args)
470   nil
471 end

add_foreign_key(name, table, opts = OPTS)

Add a foreign key with the given name and referencing the given table. See CreateTableGenerator#column for the available options.

You can also pass an array of column names for creating composite foreign keys. In this case, it will assume the columns exist and will only add the constraint. You can provide a :name option to name the constraint.

NOTE: If you need to add a foreign key constraint to a single existing column use the composite key syntax even if it is only one column.

add_foreign_key(:artist_id, :table) # ADD COLUMN artist_id integer REFERENCES table
add_foreign_key([:name], :table) # ADD FOREIGN KEY (name) REFERENCES table

PostgreSQL specific options:

:not_valid

Set to true to add the constraint with the NOT VALID syntax. This makes it so that future inserts must respect referential integrity, but allows the constraint to be added even if existing column values reference rows that do not exist. After all the existing data has been cleaned up, validate_constraint can be used to mark the constraint as valid. Note that this option only makes sense when using an array of columns.

    # File lib/sequel/database/schema_generator.rb
516 def add_foreign_key(name, table, opts = OPTS)
517   return add_composite_foreign_key(name, table, opts) if name.is_a?(Array)
518   add_column(name, Integer, {:table=>table}.merge!(opts))
519 end

add_full_text_index(columns, opts = OPTS)

Add a full text index on the given columns. See CreateTableGenerator#full_text_index for available options.

    # File lib/sequel/database/schema_generator.rb
523 def add_full_text_index(columns, opts = OPTS)
524   add_index(columns, {:type=>:full_text}.merge!(opts))
525 end

add_index(columns, opts = OPTS)

Add an index on the given columns. See CreateTableGenerator#index for available options.

add_index(:artist_id) # CREATE INDEX table_artist_id_index ON table (artist_id)

    # File lib/sequel/database/schema_generator.rb
531 def add_index(columns, opts = OPTS)
532   @operations << {:op => :add_index, :columns => Array(columns)}.merge!(opts)
533   nil
534 end

add_primary_key(name, opts = OPTS)

Add a primary key. See CreateTableGenerator#column for the available options. Like add_foreign_key, if you specify the column name as an array, it just creates a constraint:

add_primary_key(:id) # ADD COLUMN id serial PRIMARY KEY
add_primary_key([:artist_id, :name]) # ADD PRIMARY KEY (artist_id, name)

PostgreSQL specific options:

:include	Include additional columns in the underlying index, to allow for index-only scans in more cases (PostgreSQL 11+).
:using_index	Use the USING INDEX clause to specify an existing unique index
:without_overlaps	Use WITHOUT OVERLAPS clause to specify an exclusion constraint on the final column (PostgreSQL 18+, composite primary keys only).

    # File lib/sequel/database/schema_generator.rb
550 def add_primary_key(name, opts = OPTS)
551   return add_composite_primary_key(name, opts) if name.is_a?(Array)
552   opts = @db.serial_primary_key_options.merge(opts)
553   add_column(name, opts.delete(:type), opts)
554 end

add_spatial_index(columns, opts = OPTS)

Add a spatial index on the given columns. See CreateTableGenerator#index for available options.

    # File lib/sequel/database/schema_generator.rb
558 def add_spatial_index(columns, opts = OPTS)
559   add_index(columns, {:type=>:spatial}.merge!(opts))
560 end

add_unique_constraint(columns, opts = OPTS)

Add a unique constraint to the given column(s)

add_unique_constraint(:name) # ADD UNIQUE (name)
add_unique_constraint(:name, name: :unique_name) # ADD CONSTRAINT unique_name UNIQUE (name)

Supports the same :deferrable option as CreateTableGenerator#column.

PostgreSQL specific options:

:include	Include additional columns in the underlying index, to allow for index-only scans in more cases (PostgreSQL 11+).
:nulls_not_distinct	Use NULLS NOT DISTINCT to setup a constraint where NULL entries are considered distinct (PostgreSQL 15+)
:using_index	Use the USING INDEX clause to specify an existing unique index
:without_overlaps	Use WITHOUT OVERLAPS clause to specify an exclusion constraint on the final column (PostgreSQL 18+, composite unique constraints only).

    # File lib/sequel/database/schema_generator.rb
489 def add_unique_constraint(columns, opts = OPTS)
490   @operations << {:op => :add_constraint, :type => :unique, :columns => Array(columns)}.merge!(opts)
491   nil
492 end

drop_column(name, opts=OPTS)

Remove a column from the table.

drop_column(:artist_id) # DROP COLUMN artist_id
drop_column(:artist_id, cascade: true) # DROP COLUMN artist_id CASCADE

Options:

:cascade

CASCADE the operation, dropping other objects that depend on the dropped column.

PostgreSQL specific options:

:if_exists

Use IF EXISTS, so no error is raised if the column does not exist.

    # File lib/sequel/database/schema_generator.rb
575 def drop_column(name, opts=OPTS)
576   @operations << {:op => :drop_column, :name => name}.merge!(opts)
577   nil
578 end

drop_constraint(name, opts=OPTS)

Remove a constraint from the table:

drop_constraint(:unique_name) # DROP CONSTRAINT unique_name
drop_constraint(:unique_name, cascade: true) # DROP CONSTRAINT unique_name CASCADE

MySQL/SQLite specific options:

:type

Set the type of constraint to drop, either :primary_key, :foreign_key, or :unique.

    # File lib/sequel/database/schema_generator.rb
589 def drop_constraint(name, opts=OPTS)
590   @operations << {:op => :drop_constraint, :name => name}.merge!(opts)
591   nil
592 end

drop_foreign_key(name, opts=OPTS)

Remove a foreign key and the associated column from the table. General options:

:name

The name of the constraint to drop. If not given, uses the same name that would be used by add_foreign_key with the same columns.

NOTE: If you want to drop only the foreign key constraint but keep the column, use the composite key syntax even if it is only one column.

drop_foreign_key(:artist_id) # DROP CONSTRAINT table_artist_id_fkey, DROP COLUMN artist_id
drop_foreign_key([:name]) # DROP CONSTRAINT table_name_fkey

    # File lib/sequel/database/schema_generator.rb
604 def drop_foreign_key(name, opts=OPTS)
605   if !name.is_a?(Array) && opts[:foreign_key_constraint_name]
606     opts = Hash[opts]
607     opts[:name] = opts[:foreign_key_constraint_name]
608   end
609   drop_composite_foreign_key(Array(name), opts)
610   drop_column(name) unless name.is_a?(Array)
611 end

drop_index(columns, options=OPTS)

Remove an index from the table. General options:

:name

The name of the index to drop. If not given, uses the same name that would be used by add_index with the same columns.

PostgreSQL specific options:

:cascade	Cascade the index drop to dependent objects.
:concurrently	Drop the index using CONCURRENTLY, which doesn’t block operations on the table. Supported in PostgreSQL 9.2+.
:if_exists	Only drop the index if it already exists.

drop_index(:artist_id) # DROP INDEX table_artist_id_index
drop_index([:a, :b]) # DROP INDEX table_a_b_index
drop_index([:a, :b], name: :foo) # DROP INDEX foo

    # File lib/sequel/database/schema_generator.rb
628 def drop_index(columns, options=OPTS)
629   @operations << {:op => :drop_index, :columns => Array(columns)}.merge!(options)
630   nil
631 end

rename_column(name, new_name, opts = OPTS)

Rename one of the table’s columns.

rename_column(:name, :artist_name) # RENAME COLUMN name TO artist_name

    # File lib/sequel/database/schema_generator.rb
636 def rename_column(name, new_name, opts = OPTS)
637   @operations << {:op => :rename_column, :name => name, :new_name => new_name}.merge!(opts)
638   nil
639 end

set_column_allow_null(name, allow_null=true)

Set a given column as allowing NULL values.

set_column_allow_null(:artist_name) # ALTER COLUMN artist_name DROP NOT NULL

On MySQL, make sure to use a symbol for the name of the column, as otherwise you can lose the default and type for the column.

    # File lib/sequel/database/schema_generator.rb
677 def set_column_allow_null(name, allow_null=true)
678   @operations << {:op => :set_column_null, :name => name, :null => allow_null}
679   nil
680 end

set_column_default(name, default)

Modify the default value for one of the table’s column.

set_column_default(:artist_name, 'a') # ALTER COLUMN artist_name SET DEFAULT 'a'

To remove an existing default value, use nil as the value:

set_column_default(:artist_name, nil) # ALTER COLUMN artist_name SET DEFAULT NULL

On MySQL, make sure to use a symbol for the name of the column, as otherwise you can lose the type and NULL/NOT NULL setting for the column.

    # File lib/sequel/database/schema_generator.rb
651 def set_column_default(name, default)
652   @operations << {:op => :set_column_default, :name => name, :default => default}
653   nil
654 end

set_column_not_null(name)

Set a given column as not allowing NULL values.

set_column_not_null(:artist_name) # ALTER COLUMN artist_name SET NOT NULL

On MySQL, make sure to use a symbol for the name of the column, as otherwise you can lose the default and type for the column.

    # File lib/sequel/database/schema_generator.rb
688 def set_column_not_null(name)
689   set_column_allow_null(name, false)
690 end

set_column_type(name, type, opts=OPTS)

Modify the type of one of the table’s column.

set_column_type(:artist_name, 'char(10)') # ALTER COLUMN artist_name TYPE char(10)

PostgreSQL specific options:

:using

Add a USING clause that specifies how to convert existing values to new values.

On MySQL, make sure to use a symbol for the name of the column, as otherwise you can lose the default and NULL/NOT NULL setting for the column.

    # File lib/sequel/database/schema_generator.rb
666 def set_column_type(name, type, opts=OPTS)
667   @operations << {:op => :set_column_type, :name => name, :type => type}.merge!(opts)
668   nil
669 end