instance method
add_index
Ruby on Rails 2.3.18
Since v2.2.3Signature
add_index(table_name, column_name, options = {})Adds a new index to the table. column_name can be a single Symbol, or an Array of Symbols.
The index will be named after the table and the first column name, unless you pass :name as an option.
When creating an index on multiple columns, the first column is used as a name for the index. For example, when you specify an index on two columns [:first, :last], the DBMS creates an index for both columns as well as an index for the first column :first. Using just the first name for this index makes sense, because you will never have to create a singular index with this name.
Examples
Creating a simple index
add_index(:suppliers, :name)
generates
CREATE INDEX suppliers_name_index ON suppliers(name)
Creating a unique index
add_index(:accounts, [:branch_id, :party_id], :unique => true)
generates
CREATE UNIQUE INDEX accounts_branch_id_party_id_index ON accounts(branch_id, party_id)
Creating a named index
add_index(:accounts, [:branch_id, :party_id], :unique => true, :name => 'by_branch_party')
generates
CREATE UNIQUE INDEX by_branch_party ON accounts(branch_id, party_id)
Creating an index with specific key length
add_index(:accounts, :name, :name => 'by_name', :length => 10)
generates
CREATE INDEX by_name ON accounts(name(10)) add_index(:accounts, [:name, :surname], :name => 'by_name_surname', :length => {:name => 10, :surname => 15})
generates
CREATE INDEX by_name_surname ON accounts(name(10), surname(15))
Note: SQLite doesn’t support index length
Parameters
-
table_namereq -
column_namereq -
optionsopt = {}
Source
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 271
def add_index(table_name, column_name, options = {})
column_names = Array(column_name)
index_name = index_name(table_name, :column => column_names)
if Hash === options # legacy support, since this param was a string
index_type = options[:unique] ? "UNIQUE" : ""
index_name = options[:name].to_s if options[:name]
else
index_type = options
end
if index_name.length > index_name_length
@logger.warn("Index name '#{index_name}' on table '#{table_name}' is too long; the limit is #{index_name_length} characters. Skipping.")
return
end
if index_exists?(table_name, index_name, false)
@logger.warn("Index name '#{index_name}' on table '#{table_name}' already exists. Skipping.")
return
end
quoted_column_names = quoted_columns_for_index(column_names, options).join(", ")
execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} (#{quoted_column_names})"
end
Defined in activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb line 271
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Defined in ActiveRecord::ConnectionAdapters::SchemaStatements