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