markdown 使用CSV文件播种Rails数据库

Posted 2021-05-06

# How to seed a Rails database with a CSV file

## 1. Setup

First, Create a folder inside of `lib` called `seeds`

Put your CSV file `example.csv` into the `lib/seeds` folder. In the example below, the file is called `real_estate_transactions.csv`

Make sure you've created a resource with the appropriate columns to match your seed data. The names don't have to match up. 

## 2. Read in a CSV file

Add the following lines to your `seeds.rb` file:

    require 'csv'

    csv_text = File.read(Rails.root.join('lib', 'seeds', 'real_estate_transactions.csv'))
    puts csv_text

The first line requires the Ruby CSV library we need to properly parse the CSV data. The next line reads in the CSV file into a variable. The last line prints the contents of the variable. When you run `rake db:seed` you should see a wall of text representing your CSV data. It's a first step, but we've still got a lot of work to do. 

We'll keep building off this code until we've created a working seeds file. You should be able to run `rake db:seed` at the end of each step

## 3. Parse the CSV

    require 'csv'

    csv_text = File.read(Rails.root.join('lib', 'seeds', 'real_estate_transactions.csv'))
    csv = CSV.parse(csv_text, :headers => true, :encoding => 'ISO-8859-1')
    puts csv

The new line converts the CSV file into a structure that Ruby can read. The `:headers => true` option tells the parser to ignore the first line of the CSV file. 

## 4. Looping through the parsed data

    require 'csv'

    csv_text = File.read(Rails.root.join('lib', 'seeds', 'real_estate_transactions.csv'))
    csv = CSV.parse(csv_text, :headers => true, :encoding => 'ISO-8859-1')
    csv.each do |row|
      puts row.to_hash
    end

This new addition loops through the entire CSV file and converts each row of the document into a hash. The headers of the CSV file will be used as keys for the hash because we added the `:headers => true` option in our previous step.

## 5. Create a database object from each row

    require 'csv'

    csv_text = File.read(Rails.root.join('lib', 'seeds', 'real_estate_transactions.csv'))
    csv = CSV.parse(csv_text, :headers => true, :encoding => 'ISO-8859-1')
    csv.each do |row|
      t = Transaction.new
      t.street = row['street']
      t.city = row['city']
      t.zip = row['zip']
      t.zip = row['zip']
      t.state = row['state']
      t.beds = row['beds']
      t.sq_feet = row['sq_feet']
      t.category = row['type']
      t.sale_date = row['sale_date']
      t.price = row['price']
      t.lat = row['latitude']
      t.lng = row['longitude']
      t.save
      puts "#{t.street}, #{t.city} saved"
    end

    puts "There are now #{Transaction.count} rows in the transactions table"