Ruby Sequel (SQlite3) "SELECT" 错误

Question

我正在使用一个ruby助手，使用续集ORM从SQLite3数据库中提取数据。这是代码：

#!/usr/bin/env ruby
# encoding: UTF-8
require_relative 'greekdate'
require 'sequel'
module Pharmacy
    class Open
        def initialize
            db = Sequel.sqlite("../lib/drama.sql")
            @address = db[:addressbook]
            @ov = db[:overnight]
            @grday = GRDay::MDate.new
        end                         
        def display
            data = @address.first(id: get_id()) # ERROR HERE
            p data[:name]
        end
        private
        def get_id
            mod_date = @grday.get[:mod_date]
            @ov.each do |entry|
                return entry[:pharmacy_id] if entry[:date].to_s == mod_date
            end
        end
    end
end

我正在调用display方法。我得到的错误是：

/Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sqlite3-1.3.7/lib/sqlite3/database.rb:91:in `initialize': SQLite3::SQLException: only a single result allowed for a SELECT that is part of an expression (Sequel::DatabaseError)
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sqlite3-1.3.7/lib/sqlite3/database.rb:91:in `new'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sqlite3-1.3.7/lib/sqlite3/database.rb:91:in `prepare'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sqlite3-1.3.7/lib/sqlite3/database.rb:263:in `query'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/adapters/sqlite.rb:179:in `block (2 levels) in _execute'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/database/logging.rb:33:in `log_yield'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/adapters/sqlite.rb:179:in `block in _execute'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/database/connecting.rb:229:in `block in synchronize'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/connection_pool/threaded.rb:104:in `hold'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/database/connecting.rb:229:in `synchronize'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/adapters/sqlite.rb:172:in `_execute'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/adapters/sqlite.rb:122:in `execute'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/dataset/actions.rb:794:in `execute'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/adapters/sqlite.rb:356:in `fetch_rows'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/dataset/actions.rb:144:in `each'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/dataset/actions.rb:584:in `single_record'
    from /Users/atma/.rvm/gems/ruby-1.9.3-p194/gems/sequel-4.0.0/lib/sequel/dataset/actions.rb:202:in `first'
    from test.rb:17:in `display'
    from test.rb:32:in `<main>'

我不知道为什么会这样。起初，我认为我应该以某种方式关闭并重新打开连接，但错误显示"作为表达式一部分的SELECT只允许一个结果"，直到昨天我才得到一个结果，我认为没有理由得到两个结果，因为我正在调用表第一个（id:X）。

任何想法和解释都非常受欢迎：-）

感谢您抽出时间，

PA

Answer 1

如果@ov中没有指定日期的条目，则get_id方法返回@ov，因为这是@ov.each的返回值。你可能想要这样的东西：

def display
    if id = get_id
      data = @address.first(id: id)
      p data[:name]
    end
end
private
def get_id
    mod_date = @grday.get[:mod_date]
    @ov.each do |entry|
        return entry[:pharmacy_id] if entry[:date].to_s == mod_date
    end
    nil
end

请注意，display对于方法名称来说是一个糟糕的选择，因为Object#display已经由ruby定义了。