Cast decimals to ruby BigDecimals

This is particularly a problem since
[0.198](https://prestodb.io/docs/current/release/release-0.198.html),
where decimal literals are now interpreted as `DECIMAL` by default,
which means a query like `SELECT 1.0` was coming through as a String.

Author: oggy

lib/presto/client/statement_client.rb

@@ -15,6 +15,7 @@
 #
 module Presto::Client
 
+  require 'bigdecimal'
   require 'json'
   require 'msgpack'
   require 'presto/client/models'
@@ -42,7 +43,8 @@ def initialize(faraday, query, options, next_uri=nil)
 
       if next_uri
         response = faraday_get_with_retry(next_uri)
-        @results = @models::QueryResults.decode(parse_body(response))
+        decoded = @models::QueryResults.decode(parse_body(response))
+        @results = cast_results(decoded)
       else
         post_query_request!
       end
@@ -69,7 +71,8 @@ def post_query_request!
         raise PrestoHttpError.new(response.status, "Failed to start query: #{response.body} (#{response.status})")
       end
 
-      @results = decode_model(uri, parse_body(response), @models::QueryResults)
+      decoded = decode_model(uri, parse_body(response), @models::QueryResults)
+      @results = cast_results(decoded)
     end
 
     private :post_query_request!
@@ -113,7 +116,8 @@ def advance
       uri = @results.next_uri
 
       response = faraday_get_with_retry(uri)
-      @results = decode_model(uri, parse_body(response), @models::QueryResults)
+      decoded = decode_model(uri, parse_body(response), @models::QueryResults)
+      @results = cast_results(decoded)
 
       return true
     end
@@ -124,6 +128,26 @@ def query_info
       decode_model(uri, parse_body(response), @models::QueryInfo)
     end
 
+    def cast_results(query_results)
+      data = query_results.data
+      columns = query_results.columns
+      return query_results if data.nil? || columns.nil?
+
+      decimal_indices = columns.each_with_index.select { |c, i| c.type.start_with?('decimal(') }.map(&:last)
+      if decimal_indices.empty?
+        query_results
+      else
+        new_data = data.map do |row|
+          copy = row.dup
+          decimal_indices.each do |index|
+            copy[index] = BigDecimal(copy[index])
+          end
+          copy
+        end
+        query_results.class.new(query_results.to_h.merge(data: new_data))
+      end
+    end
+
     def decode_model(uri, hash, body_class)
       begin
         body_class.decode(hash)

spec/statement_client_spec.rb

@@ -43,6 +43,36 @@
     StatementClient.new(faraday, query, options)
   end
 
+  it "returns results correctly" do
+    query = 'select 1 as i, 1.0 as d'
+    stub_request(:post, "localhost/v1/statement").
+      with(body: query,
+           headers: {
+              "User-Agent" => "presto-ruby/#{VERSION}",
+              "X-Presto-Catalog" => options[:catalog],
+              "X-Presto-Schema" => options[:schema],
+              "X-Presto-User" => options[:user],
+              "X-Presto-Language" => options[:language],
+              "X-Presto-Time-Zone" => options[:time_zone],
+    }).to_return(body: <<-JSON)
+      {"id":"queryid","infoUri":"http://localhost/ui/query.html?queryid","nextUri":"http://localhost/v1/statement/queryid/1","stats":{"state":"QUEUED","queued":true,"scheduled":false,"nodes":0,"totalSplits":0,"queuedSplits":0,"runningSplits":0,"completedSplits":0,"userTimeMillis":0,"cpuTimeMillis":0,"wallTimeMillis":0,"queuedTimeMillis":0,"elapsedTimeMillis":0,"processedRows":0,"processedBytes":0,"peakMemoryBytes":0}}
+    JSON
+    client = StatementClient.new(faraday, query, options)
+    client.current_results.data.should be_nil
+
+    stub_request(:get, "http://localhost/v1/statement/queryid/1").to_return(body: <<-JSON)
+      {"id":"20180927_190533_00177_setx5","infoUri":"http://localhost/ui/query.html?queryid","partialCancelUri":"http://192.168.128.77:8091/v1/stage/queryid.0","nextUri":"http://localhost/v1/statement/queryid/2","columns":[{"name":"i","type":"integer","typeSignature":{"rawType":"integer","typeArguments":[],"literalArguments":[],"arguments":[]}},{"name":"d","type":"decimal(2,1)","typeSignature":{"rawType":"decimal","typeArguments":[],"literalArguments":[],"arguments":[{"kind":"LONG_LITERAL","value":2},{"kind":"LONG_LITERAL","value":1}]}}],"data":[[1,"1.0"]],"stats":{"state":"RUNNING","queued":false,"scheduled":true,"nodes":1,"totalSplits":17,"queuedSplits":17,"runningSplits":0,"completedSplits":0,"userTimeMillis":0,"cpuTimeMillis":0,"wallTimeMillis":0,"queuedTimeMillis":1,"elapsedTimeMillis":121,"processedRows":0,"processedBytes":0,"peakMemoryBytes":0,"rootStage":{"stageId":"0","state":"RUNNING","done":false,"nodes":1,"totalSplits":17,"queuedSplits":17,"runningSplits":0,"completedSplits":0,"userTimeMillis":0,"cpuTimeMillis":0,"wallTimeMillis":0,"processedRows":0,"processedBytes":0,"subStages":[]},"progressPercentage":0.0}}
+    JSON
+    client.advance.should be_true
+    client.current_results.data.should == [[1, BigDecimal('1.0')]]
+
+    stub_request(:get, "http://localhost/v1/statement/queryid/2").to_return(body: <<-JSON)
+      {"id":"queryid","infoUri":"http://localhost/ui/query.html?queryid","columns":[{"name":"i","type":"integer","typeSignature":{"rawType":"integer","typeArguments":[],"literalArguments":[],"arguments":[]}},{"name":"d","type":"decimal(2,1)","typeSignature":{"rawType":"decimal","typeArguments":[],"literalArguments":[],"arguments":[{"kind":"LONG_LITERAL","value":2},{"kind":"LONG_LITERAL","value":1}]}}],"stats":{"state":"FINISHED","queued":false,"scheduled":true,"nodes":1,"totalSplits":17,"queuedSplits":0,"runningSplits":0,"completedSplits":17,"userTimeMillis":4,"cpuTimeMillis":5,"wallTimeMillis":109,"queuedTimeMillis":1,"elapsedTimeMillis":128,"processedRows":0,"processedBytes":0,"peakMemoryBytes":0,"rootStage":{"stageId":"0","state":"FINISHED","done":true,"nodes":1,"totalSplits":17,"queuedSplits":0,"runningSplits":0,"completedSplits":17,"userTimeMillis":4,"cpuTimeMillis":5,"wallTimeMillis":109,"processedRows":1,"processedBytes":0,"subStages":[]},"progressPercentage":100.0}}
+    JSON
+    client.advance.should be_true
+    client.current_results.data.should be_nil
+  end
+
   let :response_json2 do
     {
       id: "queryid",
@@ -402,4 +432,3 @@
     StatementClient.new(faraday, query, options)
   end
 end
-