Rome::Collection(T)

Build Database Queries.

A Collection is immutable: all methods will return a copy of the previous Collection with the added constraint(s). For example:

users = User.select(:id, :name).where(group_id: 2)

Termination methods such as #find_by, or #take will explicitely execute a SQL request against the database and load one record.

first_user = users.order(:name).take
# => SELECT "id", "name"
#    FROM "users"
#    WHERE "group_id" = 2
#    ORDER BY "name" ASC
#    LIMIT 1;

Termination methods such as #to_a or #each will execute a SQL request then cache loaded records into the Collection, so further accesses won't re-execute the SQL request. Some methods such as #first or #size will leverage this cache when it's available.

users.to_a
# => SELECT "id", "name" FROM "users" WHERE "group_id" = 2;

When specifying column names you should always use a Symbol, so they'll be properly quoted for the database server. In many cases you can specify raw SQL statements using a String. For example:

users = User.where("LENGTH(name) > ?", 10)
# => SELECT * FROM "users" WHERE LENGTH(name) > 10;

users = User.order("LENGTH(name) DESC")
# => SELECT * FROM "users" ORDER BY LENGTH(name) DESC;

count = User.count("LENGTH(name)", distinct: true)
# => SELECT COUNT(DISTINCT LENGTH(name)) FROM "users";