Parse XML using Nokogiri in Rails to compare a database table

Question

I have a table called "users", which has three columns:

id, ref, name

I want to parse the following XML document using Nokogiri and list the matched and unmatched records by comparing the values in the "users" table records:

<?xml version="1.0" encoding="UTF-8"?>
<EXPORT>
  <DETAIL>
    <ID>150</ID>
    <REF>188440</REF>
    <USER>Bruce</USER>
  </DETAIL>
    <DETAIL>
    <ID>1501003</ID>
    <REF>1884402</REF>
    <USER>Alice</USER>
  </DETAIL>
</EXPORT>

For example:

Users.where(id: 1501003).name
Users.where(ref: 188440).name

Find the name by comparing the id and ref.

Note: if id does not match, then compare with ref. If id matches then ignore ref.

I tried:

doc = Nokogiri::XML(File.open(self.filename))
exp = "//EXPORT/DETAIL"

NODES = doc.xpath(exp)

nodes.each do |node|
  unless node.text.nil?
    User.where(id: node.text).first.name
end

Please explain why you want to use Nokogiri to do lookups from what appears to be a database dump in XML. That seems terribly awkward and a very slow and fragile solution. If the data is in a database search against it. If it's not and you want to find records to load then load the data into a separate table and select the desired records from it and insert into the master. A DB XML dump can easily exceed available RAM making your plan unviable. Using a SAX parser might help but still, there's smell to the solution. meta.stackexchange.com/questions/66377/what-is-the-xy-problem — the Tin Man
– the Tin Man, Commented Sep 10, 2015 at 15:53

Community · Accepted Answer · 2017-03-20 10:29:31Z

3

I wonder why you want to use Nokogiri to do lookups from what appears to be a database dump in XML. That seems terribly awkward and a very slow and fragile solution.

A database XML dump can easily exceed available RAM making your plan unviable. Using a SAX parser might help but still, there's smell to the solution. See "What is the XY problem?".

If the data is already in a database, search against it and select the records you need.
If it's not and you want to find records to load, then load the data into a separate table and select the desired records from it and insert them into the master.

edited Mar 20, 2017 at 10:29

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answered Sep 10, 2015 at 16:01

the Tin Man

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1 Comment

Learner Over a year ago

Thank you very much Tin Man

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