insert using mysql2 gem
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Interact with Mysql Server using mysql2 gem [Part 2] – Insert and Update Operations

This is the second part of the series where we create a service to interact with MySQL server in Rails using mysql2 gem. You can read the first part here.

Requirements

  • [x] Service to connect with external MySQL server
  • [ ] Perform basic query: select, insert and update
  • [ ] Prepared statement
  • [ ] Perform transaction
  • [ ] Perform join query

In the previous blog, we created a service and also added a method to perform select operations. Today we will be adding additional methods to help us perform insert and update operations to MySQL server using mysql2 gem.

In this blog

We will be learning the following in this blog:

  • Perform insert query
  • Perform update query

Perform Insert Query

Insert query is used to create a new record in the database.

Code

def insert(attributes)
  query = format_insert_query(attributes)

  perform_mysql_operation do
    mysql_connect.query(query)

    puts 'Record inserted!'
  end
end

private

def format_insert_query(attributes)
  raise 'Attributes cannot be empty' if attributes.empty?

  columns = attributes.keys.join(',')

  values = attributes.values.collect! { |value| "'#{value}'" }.join(',')

  "INSERT INTO #{table} (#{columns}) VALUES (#{values})"
end

Explanation

format_insert_query is taking attributes hash parameter from insert method. The following is happening inside the method:

  • Get column names by formatting key part of attributes param
  • Get values to insert by formatting value part of attributes param
  • Construct and return an insert query

Following is happening inside insert method:

  • Call format_insert_query to get a query that can directly be used for the insert operation
  • Insert to database

Practically:

  • {first_name: 'John', last_name: 'Doe'} will be received as attributes parameter, which will be sent to format_insert_query to get formatted query
  • Inside format_insert_query, columns will have value "first_name,last_name"; key part of the attributes hash, values will have "'John','Doe'"; value part of the attributes hash. Lastly, if table was users it will return "INSERT INTO users (first_name,last_name) VALUES ('John','Doe')"
  • Now the insert method will send the query to the server and the new record will be inserted into the database.

Perform Update Query

Update query is used to update existing records in the database.

Code

def update(id, attributes)
  query = format_update_query(id, attributes)

  perform_mysql_operation do
    mysql_connect.query(query)

    puts 'Record Updated!'
  end
end

private

def format_update_query(id, attributes)
  raise 'Attributes cannot be empty' if attributes.empty?

  formatted_attributes = attributes.map { |key, value| "#{key}='#{value}'" }.join(',')

  "UPDATE #{table} SET #{formatted_attributes} WHERE #{primary_column}=#{id}"
end

Explanation

Only change in update to insert is; it’s also taking id as parameters. id lets us know which existing record we want to update in the database. It is getting formatted query and updating in a database, the concept is the same as insert with only change in the query.

format_update_query has a slight difference to that of format_insert_query; it is converting attributes differently, let’s see that with a practical example below.

  • If we are providing id=1 and attributes same as insert query, format_update_query will return "UPDATE users SET first_name='John',last_name='Doe' WHERE id=1"
  • Now the update method will send the query to the server and update the record with id=1 in the database.

Final Code

If you have been following the tutorial from part 1, you will have the following in your service file:

require 'mysql2'

module MySqlServer
  module Database
    class Connect
      attr_reader :mysql_connect, :table, :primary_column

      def initialize(table, primary_column)
        @table = table
        @primary_column = primary_column
      end

      def fetch_all
        perform_mysql_operation do
          result = mysql_connect.query("SELECT * from #{table}")

          puts result.entries
        end
      end

      def fetch_one(id)
        perform_mysql_operation do
          result = mysql_connect.query("SELECT * from #{table} WHERE #{primary_column}=#{id}")

          puts result.entries
        end
      end

      def insert(attributes)
        query = format_insert_query(attributes)

        perform_mysql_operation do
          mysql_connect.query(query)

          puts 'Record inserted!'
        end
      end

      def update(id, attributes)
        query = format_update_query(id, attributes)

        perform_mysql_operation do
          mysql_connect.query(query)

          puts 'Record Updated!'
        end
      end

      private

      def connect_to_db
        host = ENV['MYSQL_SERVER_IP']
        database = ENV['MYSQL_DB_NAME']
        username = ENV['MYSQL_USERNAME']
        password = ENV['MYSQL_PASSWORD']

        Mysql2::Client.new(username: username, password: password, database: database, host: host)
      end

      def perform_mysql_operation
        raise ArgumentError, 'No block was given' unless block_given?

        begin
          @mysql_connect = connect_to_db

          yield
        rescue StandardError => e
          raise e
        ensure
          mysql_connect&.close
        end
      end

      def format_insert_query(attributes)
        raise 'Attributes cannot be empty' if attributes.empty?

        columns = attributes.keys.join(',')

        values = attributes.values.collect! { |value| "'#{value}'" }.join(',')

        "INSERT INTO #{table} (#{columns}) VALUES (#{values})"
      end

      def format_update_query(id, attributes)
        raise 'Attributes cannot be empty' if attributes.empty?

        formatted_attributes = attributes.map { |key, value| "#{key}='#{value}'" }.join(',')

        "UPDATE #{table} SET #{formatted_attributes} WHERE #{primary_column}=#{id}"
      end
    end
  end
end

After this our service should be able to perform basic queries in the external MySQL server using mysql2 gem. Next week we will be learning how we can perform queries with the prepared statement which helps us to avoid SQL injection issues.

Image Credits: Cover Image by Kelvin Yang on Unsplash

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