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mongodbelixirphoenix-framework

Deep queries with mongodb driver in phoenix/elixir

I am using the mongodb driver from https://github.com/ankhers/mongodb to query a mongodb database in an elixir/phoenix project. A simple query such as 

cursor = Mongo.find(:mongo, "posts",%{})
      list = Enum.to_list(cursor)
      object= Enum.fetch(list,0)
      object= elem(object, 1) 
      new_list=Map.fetch(object, "name")
      new_list=elem(new_list,1)
      new_cursor= Mongo.find(:mongo, "posts",%{"name" => new_list})
      new_list=Enum.to_list(new_cursor)

is no problem, but I am wondering how to perform deeper searches as I have nested jsons such as 

{"posts":{"name":"something","attributes":{"aspect":{"and_so_on":"endpoint"}}}}.

So how to get to "endpoint" in this case ?

Solution

  • Your code is extremely not idiomatic, in the first place. One should not reassign values on each step, we usually use pipes Kernel.|>/2 instead.

    That said, your original cursor might be written as

    list =
  :mongo
  |> Mongo.find("posts", %{})
  |> Enum.fetch(0)
  |> elem(1) 
  |> Map.fetch("name")
  |> elem(1)
new_list =
  :mongo
  |> Mongo.find("posts", %{"name" => list})
  |> Enum.to_list()

    or, better, with pattern matching

    %{"name" => one} =
  Mongo.find_one(:mongo, "posts", %{})
one
#⇒ "something"

    MongoDB also supports mongo query language in Mongo.find/4 as shown in examples here. To get to the nested element one might do:

    Mongo.find(:mongo, "posts",
  %{"attributes" => %{"aspect" => "and_so_on"}})