Core » Commands
Commands are used to make changes in your data. Every adapter provides its own command specializations, that can use database-specific features.
Core commands include following types:
:create- a command which inserts new tuples:update- a command which updates existing tuples:delete- a command which deletes existing tuples
Working with commands
You can get a command object via Relation#command interface. All core command types are
supported by this method.
Assuming you have a users relation available:
:create command example
# inserting a single tuple
create_user = users.command(:create)
create_user.call(name: "Jane")
# inserting a multiple tuples
create_user = users.command(:create, result: :many)
create_user.call([{ name: "Jane" }, { name: "John" }])
:update command example
update_user = users.by_pk(1).command(:update)
update_user.call(name: "Jane Doe")
:delete command example
delete_user = users.by_pk(1).command(:delete)
delete_user.call
Using custom command types
You can define custom command types too. This is useful when the logic is complex and you prefer to encapsulate it in a single class.
class MyCommand < ROM::SQL::Commands::Create
relation :users
register_as :my_command
def execute(tuple)
# do whatever you need
end
end
When your command is available in the configured rom container, you can get it in the standard way:
my_command = users.command(:my_command)
my_command.call(name: "Jane")
Commands vs Changesets
Commands are the underlying abstraction for making changes in your database, whereas changesets should be treated as a more advanced abstraction, which provides additional data mapping functionality, and support for associating data.
For consistency, you should consider using changesets instead of commands; however, if you're processing larger amounts of data, and performance is a concern, you may want to use commands instead.
Here are benchmarks showing you roughly performance difference between the two:
=> benchmark: create command vs changeset
Warming up --------------------------------------
command 226.000 i/100ms
changeset 152.000 i/100ms
Calculating -------------------------------------
command 2.238k (±10.5%) i/s - 11.300k in 5.134520s
changeset 1.416k (±17.1%) i/s - 6.840k in 5.035512s
Comparison:
command: 2237.6 i/s
changeset: 1415.6 i/s - 1.58x slower
=> benchmark: update command vs changeset
Warming up --------------------------------------
command 35.000 i/100ms
changeset 21.000 i/100ms
Calculating -------------------------------------
command 405.284 (± 3.5%) i/s - 2.030k in 5.014935s
changeset 213.359 (± 4.2%) i/s - 1.071k in 5.028808s
Comparison:
command: 405.3 i/s
changeset: 213.4 i/s - 1.90x slower
=> benchmark: delete command vs changeset
Warming up --------------------------------------
command 230.000 i/100ms
changeset 134.000 i/100ms
Calculating -------------------------------------
command 2.280k (± 5.0%) i/s - 11.500k in 5.057193s
changeset 1.452k (±14.9%) i/s - 7.102k in 5.044861s
Comparison:
command: 2280.2 i/s
changeset: 1451.5 i/s - 1.57x slower