Exploring Graphs with Elixir/

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Inspect the Structs

Inspect the Structs

Learn how to create a graph using the graph struct and to inspect the struct by defining a user-friendly view.

We'll cover the following...

Let’s try out the %GraphCommons.Graph{} struct by creating a new graph. We’ll use a property graph model example here, which generates a minimal graph with two nodes and one edge between them.

Note: Our query.ex file will be similar to the graph.ex file with the term “graph” replaced with “query.”

Default graph

The following example will serve as our default graph.

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Default graph
Default graph

We can create this simple graph with the Cypher string:

iex> CREATE (a)-[:EX]->(b)

Here is the complete command:

iex> "CREATE (a)-[:EX]->(b)" |>
...> GraphCommons.Graph.new("test.cypher", :property)

Run the terminal, and enter the command below:

#---
# Excerpted from "Exploring Graphs with Elixir",
# published by The Pragmatic Bookshelf.
# Copyrights apply to this code. It may not be used to create training material,
# courses, books, articles, and the like. Contact us if you are in doubt.
# We make no guarantees that this code is fit for any purpose.
# Visit http://www.pragmaticprogrammer.com/titles/thgraphs for more book information.
#---
defmodule GraphCommons.Query do

  ## ATTRIBUTES

  @storage_dir GraphCommons.storage_dir()

  ## STRUCT

  @enforce_keys ~w[data file type]a
  defstruct ~w[data file path type uri]a

  ## TYPES

  @type query_data :: String.t()
  @type query_file :: String.t()
  @type query_path :: String.t()
  @type query_type :: GraphCommons.query_type()
  @type query_uri :: String.t()

  @type t :: %__MODULE__{
          # user
          data: query_data,
          file: query_file,
          type: query_type,
          # system
          path: query_path,
          uri: query_uri
        }

  defguard is_query_type(query_type)
           when query_type in [ :dgraph, :native, :property, :rdf, :tinker ]

  ## CONSTRUCTOR

  def new(query_data, query_file, query_type)
      when is_query_type(query_type) do
    query_path = "#{@storage_dir}/#{query_type}/queries/#{query_file}"

    %__MODULE__{
      # user
      data: query_data,
      file: query_file,
      type: query_type,
      # system
      path: query_path,
      uri: "file://" <> query_path
    }
  end

  ## FUNCTIONS

  def queries_dir(query_type), do: "#{@storage_dir}/#{query_type}/queries/"

  @type file_test :: GraphCommons.file_test()

  def list_queries(query_type, file_test \\ :exists?) do
    list_queries_dir("", query_type, file_test)
  end

  def list_queries_dir(query_file, query_type, file_test \\ :exists?) do
    path = "#{@storage_dir}/#{query_type}/queries/"

    (path <> query_file)
    |> File.ls!()
    |> do_filter(path, file_test)
    |> Enum.sort()
    |> Enum.map(fn f ->
      File.dir?(path <> f)
      |> case do
        true -> "#{String.upcase(f)}"
        false -> f
      end
    end)
  end

  defp do_filter(files, path, file_test) do
    files
    |> Enum.filter(fn f ->
      case file_test do
        :dir? -> File.dir?(path <> f)
        :regular? -> File.regular?(path <> f)
        :exists? -> true
      end
    end)
  end

  def read_query(query_file, query_type)
      when query_file != "" and is_query_type(query_type) do
    queries_dir = "#{@storage_dir}/#{query_type}/queries/"
    query_data = File.read!(queries_dir <> query_file)

    new(query_data, query_file, query_type)
  end

  def write_query(query_data, query_file, query_type)
      when query_data != "" and
             query_file != "" and is_query_type(query_type) do
    queries_dir = "#{@storage_dir}/#{query_type}/queries/"
    File.write!(queries_dir <> query_file, query_data)

    new(query_data, query_file, query_type)
  end

  ## MACROS

  defmacro __using__(opts) do
    query_type = Keyword.get(opts, :query_type)
    # query_module = Keyword.get(opts, :query_module)

    quote do

      ## TYPES

      @type query_file_test :: GraphCommons.file_test()

      @type query_data :: GraphCommons.Query.query_data()
      @type query_file :: GraphCommons.Query.query_file()
      @type query_path :: GraphCommons.Query.query_path()
      @type query_type :: GraphCommons.Query.query_type()
      @type query_uri :: GraphCommons.Query.query_uri()

      @type query_t :: GraphCommons.Query.t()

      ## FUNCTIONS

      # 
      # def graph_service(), do: unquote(graph_module)
      # 

      def list_queries(query_file_test \\ :exists?),
        do: GraphCommons.Query.list_queries(
          unquote(query_type), query_file_test)

      def list_queries_dir(dir, query_file_test \\ :exists?),
        do: GraphCommons.Query.list_queries_dir(dir,
          unquote(query_type), query_file_test)

      def new_query(query_data), do: new_query(query_data, "")

      def new_query(query_data, query_file),
        do: GraphCommons.Query.new(query_data, query_file,
          unquote(query_type))

      def read_query(query_file),
        do: GraphCommons.Query.read_query(query_file,
          unquote(query_type))

      def write_query(query_data, query_file),
        do: GraphCommons.Query.write_query(query_data, query_file,
          unquote(query_type))
    end
  end

  ## IMPLEMENTATIONS

end
Create the default graph
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