How can I iterate through a MySQL result set?

问题:

Here is the code I'm using:

# Run the query against the database defined in .yml file.
# This is a Mysql::result object - http://www.tmtm.org/en/mysql/ruby/
@results = ActiveRecord::Base.connection.execute(@sql_query)

In my View, here's what I do to see the values:

<pre><%= debug @results %></pre>
Outputs: #<Mysql2::Result:0x007f31849a1fc0>

<% @results.each do |val| %>
   <%= val %>
<% end %>
Outputs: ["asdfasdf", 23, "qwefqwef"] ["sdfgdsf", 23, "asdfasdfasdf"]

So imagine I query something like select * from Person, and that returns a result set such as:

ID      Name      Age
1       Sergio    22
2       Lazlow    28
3       Zeus      47

How can I iterate through each value and output it?

The documentation here is not useful because I have tried methods that supposedly exist, but the interpreter gives me an error saying that those methods don't exist. Am I using the wrong documentation?

http://www.tmtm.org/en/mysql/ruby/

Thanks!

回答1:

If you are using mysql2 gem then you should be getting the mysql2 result object and according to the docs you should be able to do the following

results.each do |row|
  # conveniently, row is a hash
  # the keys are the fields, as you'd expect
  # the values are pre-built ruby primitives mapped from their corresponding field types in MySQL
  # Here's an otter: http://farm1.static.flickr.com/130/398077070_b8795d0ef3_b.jpg
end

Checkout the documentation here

So in you case you can do the following

<% @results.each do |val| %>
   <%= "#{val['id']}, #{val['name']}, #{val['age']}" %>
<% end %>

Edit: you seem to be referring to the wrong doc check the Mysql2 gems doc.

回答2:

You could try using ActiveRecord::Base.connection.exec_query instead of ActiveRecord::Base.connection.execute which returns a ActiveRecord::Result (available in rails 3.1+)

Then you can access it in various ways like .rows, .each, or .to_hash

From the docs:

result = ActiveRecord::Base.connection.exec_query('SELECT id, title, body FROM posts')
result # => #<ActiveRecord::Result:0xdeadbeef>


# Get the column names of the result:
result.columns
# => ["id", "title", "body"]

# Get the record values of the result:
result.rows
# => [[1, "title_1", "body_1"],
      [2, "title_2", "body_2"],
      ...
     ]

# Get an array of hashes representing the result (column => value):
result.to_hash
# => [{"id" => 1, "title" => "title_1", "body" => "body_1"},
      {"id" => 2, "title" => "title_2", "body" => "body_2"},
      ...
     ]

# ActiveRecord::Result also includes Enumerable.
result.each do |row|
  puts row['title'] + " " + row['body']
end

回答3:

Use :as => :hash:

raw = ActiveRecord::Base.connection.execute(sql)
raw.each(:as => :hash) do |row|
  puts row.inspect # row is hash
end

回答4:

Look for @results.fields for column header.

Example: @results = [[1, "Sergio", 22],[2, "Lazlow", 28],[3, "Zeus", 47]]

@results.fields do |f|
  puts "#{f}\t"  # Column names
end

puts "\n"

@results.each do |rows| # Iterate through each row
  rows.each do |col| # Iterate through each column of the row
    puts "#{col}\t"
  end
  puts "\n"
end

Hope it is helpful.