mvellandi

mvellandi

Exploring Graphs with Elixir: Missing behaviour import, struct, cypher file (p.181)

Exploring Graphs with Elixir by @tonyhammond: P.181 — Ch 5 > Setting Up a Graph Service > API Demo

After starting iex in the umbrella project, then importing PropertyGraph, we are told to call:

iex>​​ ​​default_graph​​ ​​=​​ ​​read_graph(​​"default.cypher"​​)​
​ 	​#GraphCommons.Graph<type: property, file: "...", data: "CREATE (a)-[:EX]...">

However, read_graph hasn’t been defined yet.
We need to first add the following to the PropertyGraph module:

use GraphCommons.Graph, graph_type: :property, graph_module: __MODULE__

From that read_graph call, I don’t recall creating nor seeing the “default.cypher” in the source codebase:
graph_commons/priv/storage/property/graphs/default.cypher

I believe perhaps a cypher file with the following should work:

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

Shortly later, we call:

iex>​​ ​​graph_info​
​%GraphCommons.Service.GraphInfo{
​ 	  labels: [],
​ 	  num_edges: 1,
​ 	  num_nodes: 2,
​ 	  type: :property
​}

For me, this returned an undefined function error for PropertyGraph.new_query/1
So I looked at the definition of graph_info/0 in the book’s previous section on p.182

def​ graph_info() ​do​
​ 	  {​:ok​, [stats]} =
​ 	    @cypher_info
​ 	    |> PropertyGraph.new_query()
​ 	    |> query_graph
​ 	
​ 	  %GraphCommons.Service.GraphInfo{
​ 	    ​type:​ ​:property​,
​ 	    ​num_nodes:​ stats[​"​​nodeCount"​],
​ 	    ​num_edges:​ stats[​"​​relCount"​],
​ 	    ​labels:​ Map.keys(stats[​"​​labels"​])
​ 	  }
​ end

I noticed
1:
Although GraphCommons.Query hasn’t been formally defined, by duplicating GraphCommons.Graph to GraphCommons.Query
and changing “graph” to “query” references and checking the module’s source codebase, we should have a new_query/3 function.

However, PropertyGraph.new_query is called here with only 2 out of 3 arguments: @cypher_info and (implicitly) the query_type
Is there a missing argument for query_file ?
I couldn’t figure this out.

2:
And for graph_info/0 to return a %GraphCommons.Service.GraphInfo{} struct, I believe we need to first define the module which I didn’t see in the source codebase. So I made one here:
graph_commons/lib/graph_commons/service/graph_info.ex

Searching the source codebase for GraphInfo structs, I found the following attributes variously used, and so defined the module as follows:

defmodule GraphCommons.Service.GraphInfo do
    defstruct ~w[type num_nodes num_edges labels density file]a
end

First Post!

mvellandi

mvellandi

Regarding #1 above, getting PropertyGraph.new_query to work with one or two arguments:
I revised the definition of “using” macro in GraphCommons.Query to use a default arg:

def new_query(query_data, query_file \\ "") do
   if unquote(query_type) in [:dgraph, :native, :property, :rdf, :tinker] do
      GraphCommons.Query.new(query_data, query_file, unquote(query_type))
   end
end

Simple fix.
A code editor’s language server may need some time to recognize this as not an issue.

If you now run PropertyGraph.graph_info/0 again and get this next error below (like I did):

{ :error,
   %Bolt.Sips.Error{
      code: "Neo.ClientError.Procedure.ProcedureNotFound", 
      message: "There is no procedure with the name `apoc.meta.stats` registered for this database instance. Please ensure you've spelled the procedure name correctly and that the procedure is properly deployed."
   }
}

It means APOC-Core, included with Neo4j, hasn’t been added as a plugin.
Lastly, the Neo4j security settings configuration may need a one-line config for enabling plugin/other resource full database access.
I’ve written another post on DevTalk with how I installed Neo4j on OSX.

Cheers

Where Next?

Popular Pragmatic Bookshelf topics Top

belgoros
Following the steps described in Chapter 6 of the book, I’m stuck with running the migration as described on page 84: bundle exec sequel...
New
brianokken
Many tasks_proj/tests directories exist in chapters 2, 3, 5 that have tests that use the custom markers smoke and get, which are not decl...
New
JohnS
I can’t setup the Rails source code. This happens in a working directory containing multiple (postgres) Rails apps. With: ruby-3.0.0 s...
New
herminiotorres
Hi! I know not the intentions behind this narrative when called, on page XI: mount() |&gt; handle_event() |&gt; render() but the correc...
New
cro
I am working on the “Your Turn” for chapter one and building out the restart button talked about on page 27. It recommends looking into ...
New
adamwoolhether
When trying to generate the protobuf .go file, I receive this error: Unknown flag: --go_opt libprotoc 3.12.3 MacOS 11.3.1 Googling ...
New
jskubick
I found an issue in Chapter 7 regarding android:backgroundTint vs app:backgroundTint. How to replicate: load chapter-7 from zipfile i...
New
digitalbias
Title: Build a Weather Station with Elixir and Nerves: Problem connecting to Postgres with Grafana on (page 64) If you follow the defau...
New
EdBorn
Title: Agile Web Development with Rails 7: (page 70) I am running windows 11 pro with rails 7.0.3 and ruby 3.1.2p20 (2022-04-12 revision...
New
davetron5000
Hello faithful readers! If you have tried to follow along in the book, you are asked to start up the dev environment via dx/build and ar...
New

Other popular topics Top

Exadra37
Please tell us what is your preferred monitor setup for programming(not gaming) and why you have chosen it. Does your monitor have eye p...
New
Rainer
My first contact with Erlang was about 2 years ago when I used RabbitMQ, which is written in Erlang, for my job. This made me curious and...
New
AstonJ
I ended up cancelling my Moonlander order as I think it’s just going to be a bit too bulky for me. I think the Planck and the Preonic (o...
New
Exadra37
I am asking for any distro that only has the bare-bones to be able to get a shell in the server and then just install the packages as we ...
New
mafinar
Crystal recently reached version 1. I had been following it for awhile but never got to really learn it. Most languages I picked up out o...
New
mafinar
This is going to be a long an frequently posted thread. While talking to a friend of mine who has taken data structure and algorithm cou...
New
PragmaticBookshelf
Author Spotlight Mike Riley @mriley This month, we turn the spotlight on Mike Riley, author of Portable Python Projects. Mike’s book ...
New
PragmaticBookshelf
Author Spotlight: Karl Stolley @karlstolley Logic! Rhetoric! Prag! Wow, what a combination. In this spotlight, we sit down with Karl ...
New
PragmaticBookshelf
Develop, deploy, and debug BEAM applications using BEAMOps: a new paradigm that focuses on scalability, fault tolerance, and owning each ...
New
AstonJ
This is cool! DEEPSEEK-V3 ON M4 MAC: BLAZING FAST INFERENCE ON APPLE SILICON We just witnessed something incredible: the largest open-s...
New

Sub Categories: