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convenience.rb
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convenience.rb
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module Sequel
class Dataset
COMMA_SEPARATOR = ', '.freeze
COUNT_OF_ALL_AS_COUNT = :count['*'.lit].as(:count)
# Returns the first record matching the conditions.
def [](*conditions)
first(*conditions)
end
# Update all records matching the conditions
# with the values specified.
def []=(conditions, values)
filter(conditions).update(values)
end
# Returns the average value for the given column.
def avg(column)
get(:avg[column])
end
# Returns true if no records exists in the dataset
def empty?
get(1).nil?
end
# Returns the first record in the dataset. If a numeric argument is
# given, it is interpreted as a limit, and then returns all
# matching records up to that limit. If no argument is passed,
# it returns the first matching record. If any other type of
# argument(s) is passed, it is given to filter and the
# first matching record is returned. If a block is given, it is used
# to filter the dataset before returning anything.
#
# Examples:
#
# ds.first => {:id=>7}
# ds.first(2) => [{:id=>6}, {:id=>4}]
# ds.order(:id).first(2) => [{:id=>1}, {:id=>2}]
# ds.first(:id=>2) => {:id=>2}
# ds.first("id = 3") => {:id=>3}
# ds.first("id = ?", 4) => {:id=>4}
# ds.first{:id > 2} => {:id=>5}
# ds.order(:id).first{:id > 2} => {:id=>3}
# ds.first{:id > 2} => {:id=>5}
# ds.first("id > ?", 4){:id < 6) => {:id=>5}
# ds.order(:id).first(2){:id < 2} => [{:id=>1}]
def first(*args, &block)
ds = block ? filter(&block) : self
if args.empty?
ds.single_record
else
args = (args.size == 1) ? args.first : args
if Integer === args
ds.limit(args).all
else
ds.filter(args).single_record
end
end
end
# Return the column value for the first matching record in the dataset.
def get(column)
select(column).single_value
end
# Returns a dataset grouped by the given column with count by group.
def group_and_count(*columns)
group(*columns).select(*(columns + [COUNT_OF_ALL_AS_COUNT])).order(:count)
end
# Returns the interval between minimum and maximum values for the given
# column.
def interval(column)
get("(max(#{literal(column)}) - min(#{literal(column)}))".lit)
end
# Reverses the order and then runs first. Note that this
# will not necessarily give you the last record in the dataset,
# unless you have an unambiguous order. If there is not
# currently an order for this dataset, raises an Error.
def last(*args, &block)
raise(Error, 'No order specified') unless @opts[:order]
reverse.first(*args, &block)
end
# Maps column values for each record in the dataset (if a column name is
# given), or performs the stock mapping functionality of Enumerable.
def map(column_name = nil, &block)
if column_name
super() {|r| r[column_name]}
else
super(&block)
end
end
# Returns the maximum value for the given column.
def max(column)
get(:max[column])
end
# Returns the minimum value for the given column.
def min(column)
get(:min[column])
end
# Inserts multiple records into the associated table. This method can be
# to efficiently insert a large amounts of records into a table. Inserts
# are automatically wrapped in a transaction.
#
# This method should be called with a columns array and an array of value arrays:
#
# dataset.multi_insert([:x, :y], [[1, 2], [3, 4]])
#
# This method can also be called with an array of hashes:
#
# dataset.multi_insert({:x => 1}, {:x => 2})
#
# Be aware that all hashes should have the same keys if you use this calling method,
# otherwise some columns could be missed or set to null instead of to default
# values.
#
# The method also accepts a :slice or :commit_every option that specifies
# the number of records to insert per transaction. This is useful especially
# when inserting a large number of records, e.g.:
#
# # this will commit every 50 records
# dataset.multi_insert(lots_of_records, :slice => 50)
def multi_insert(*args)
if args.empty?
return
elsif args[0].is_a?(Array) && args[1].is_a?(Array)
columns, values, opts = *args
elsif args[0].is_a?(Array) && args[1].is_a?(Dataset)
table = @opts[:from].first
columns, dataset = *args
sql = "INSERT INTO #{quote_identifier(table)} #{literal(columns)} VALUES #{literal(dataset)}"
return @db.transaction{execute_dui(sql)}
else
# we assume that an array of hashes is given
hashes, opts = *args
return if hashes.empty?
columns = hashes.first.keys
# convert the hashes into arrays
values = hashes.map {|h| columns.map {|c| h[c]}}
end
# make sure there's work to do
return if columns.empty? || values.empty?
slice_size = opts && (opts[:commit_every] || opts[:slice])
if slice_size
values.each_slice(slice_size) do |slice|
statements = multi_insert_sql(columns, slice)
@db.transaction{statements.each{|st| execute_dui(st)}}
end
else
statements = multi_insert_sql(columns, values)
@db.transaction{statements.each{|st| execute_dui(st)}}
end
end
alias_method :import, :multi_insert
# Pretty prints the records in the dataset as plain-text table.
def print(*cols)
Sequel::PrettyTable.print(naked.all, cols.empty? ? columns : cols)
end
# Returns a Range object made from the minimum and maximum values for the
# given column.
def range(column)
if r = select(:min[column].as(:v1), :max[column].as(:v2)).first
(r[:v1]..r[:v2])
end
end
# Returns the first record in the dataset.
def single_record(opts = nil)
each((opts||{}).merge(:limit=>1)){|r| return r}
nil
end
# Returns the first value of the first record in the dataset.
# Returns nil if dataset is empty.
def single_value(opts = nil)
if r = single_record((opts||{}).merge(:graph=>false, :naked=>true))
r.values.first
end
end
# Returns the sum for the given column.
def sum(column)
get(:sum[column])
end
# Returns true if the table exists. Will raise an error
# if the dataset has fixed SQL or selects from another dataset
# or more than one table.
def table_exists?
if @opts[:sql]
raise Sequel::Error, "this dataset has fixed SQL"
end
if @opts[:from].size != 1
raise Sequel::Error, "this dataset selects from multiple sources"
end
t = @opts[:from].first
if t.is_a?(Dataset)
raise Sequel::Error, "this dataset selects from a sub query"
end
@db.table_exists?(t.to_sym)
end
# Returns a string in CSV format containing the dataset records. By
# default the CSV representation includes the column titles in the
# first line. You can turn that off by passing false as the
# include_column_titles argument.
#
# This does not use a CSV library or handle quoting of values in
# any way. If any values in any of the rows could include commas or line
# endings, you probably shouldn't use this.
def to_csv(include_column_titles = true)
n = naked
cols = n.columns
csv = ''
csv << "#{cols.join(COMMA_SEPARATOR)}\r\n" if include_column_titles
n.each{|r| csv << "#{cols.collect{|c| r[c]}.join(COMMA_SEPARATOR)}\r\n"}
csv
end
# Returns a hash with one column used as key and another used as value.
# If rows have duplicate values for the key column, the latter row(s)
# will overwrite the value of the previous row(s). If the value_column
# is not given or nil, uses the entire hash as the value.
def to_hash(key_column, value_column = nil)
inject({}) do |m, r|
m[r[key_column]] = value_column ? r[value_column] : r
m
end
end
end
end