Update Attribute In A DynamoDB Row With Ruby, AWS SDK

Question

So I'm trying to update an attribute in a DynamoDB row using Ruby. What I need to do is to a "query" for one row. Then, I need to update an attribute in that row. I've picked through the documentation quite a bit, but I'm not having any luck.

Does anyone have a good way to do this? Thanks in advance for any help!

Answer 1

You can query a table thusly: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/GettingStarted.Query.html

  # Queries for movies that were released in the specified year.
  #
  # @param year [Integer] The year to query.
  # @return [Array] The list of movies that were released in the specified year.
  def query_movies(year)
    response = @table.query(
      key_condition_expression: "#yr = :year",
      expression_attribute_names: {"#yr" => "year"},
      expression_attribute_values: {":year" => year})
  rescue Aws::Errors::ServiceError => e
    puts("Couldn't query for movies released in #{year}. Here's why:")
    puts("\t#{e.code}: #{e.message}")
    raise
  else
    response.items
  end

And to update an item: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/example_dynamodb_UpdateItem_section.html

  # Updates rating and plot data for a movie in the table.
  #
  # @param title [String] The title of the movie to update.
  # @param year [Int] The release year of the movie to update.
  # @param rating [Float] The updated rating to give the movie.
  # @param plot [String] The updated plot summary to give the movie.
  # @return [Hash] The fields that were updated, with their new values.
  def update_movie(title:, year:, rating:, plot:)
    response = @table.update_item(
      key: {"year" => year, "title" => title},
      update_expression: "set info.rating=:r, info.plot=:p",
      expression_attribute_values: { ":r" => rating, ":p" => plot },
      return_values: "UPDATED_NEW")
  rescue Aws::Errors::ServiceError => e
    puts("Couldn't update movie #{title} in table #{@table.name}. Here's why:")
    puts("\t#{e.code}: #{e.message}")
    raise
  else
    response.attributes
  end