Fix exception handling in select_all to raise errors instead of returning empty results

Fixes #50

When ClickHouse returns error responses with an 'exception' field in the JSON body
(but without HTTP error codes), the Factory.response method was silently treating
these as empty result sets instead of raising exceptions. This caused invalid queries
to return [] instead of raising DbException.

Changes:
- Add exception detection in Response::Factory.response before processing body
- Raise DbException when response body contains 'exception' field
- Add comprehensive unit tests for Factory.response with error scenarios
- Add integration tests for select_all, select_one, and select_value error handling

All 143 tests pass with no regressions.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: cv

lib/click_house/response/factory.rb

@@ -12,6 +12,12 @@ class Factory
       def self.response(faraday, config)
         body = faraday.body
 
+        # Check for exception in response body (ClickHouse may return errors with HTTP 200)
+        # This handles cases where the RaiseError middleware doesn't catch the error
+        if body.is_a?(Hash) && body.key?('exception')
+          raise DbException, body['exception']
+        end
+
         # wrap to be able to use connection#select_one, connection#select_value
         # with other formats like binary
         return raw(faraday, config) unless body.is_a?(Hash)

spec/click_house/extend/connection_selective_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 RSpec.describe ClickHouse::Extend::ConnectionSelective do
   subject do
     ClickHouse.connection
@@ -21,6 +23,12 @@
         expect(subject.select_value('SELECT 1, 2, 3, 4, 5')).to eq(1)
       end
     end
+
+    context 'when invalid query' do
+      it 'raises DbException for unknown function' do
+        expect { subject.select_value('SELECT unknownFunction()') }.to raise_error(ClickHouse::DbException)
+      end
+    end
   end
 
   describe '#select_one' do
@@ -35,6 +43,12 @@
         expect(subject.select_one('SELECT NULL')).to eq({ 'NULL' => nil })
       end
     end
+
+    context 'when invalid query' do
+      it 'raises DbException for unknown function' do
+        expect { subject.select_one('SELECT unknownFunction()') }.to raise_error(ClickHouse::DbException)
+      end
+    end
   end
 
   describe '#select_all' do
@@ -66,5 +80,19 @@
         expect(subject.select_all('SELECT * FROM rspec').to_a).to match_array(expectation)
       end
     end
+
+    context 'when invalid query' do
+      it 'raises DbException for unknown function' do
+        expect { subject.select_all('SELECT unknownFunction()') }.to raise_error(ClickHouse::DbException)
+      end
+
+      it 'raises DbException for non-existent table' do
+        expect { subject.select_all('SELECT * FROM nonexistent_table_xyz') }.to raise_error(ClickHouse::DbException)
+      end
+
+      it 'raises DbException with error message for invalid syntax' do
+        expect { subject.select_all('SELECT * FROM') }.to raise_error(ClickHouse::DbException, /Exception/)
+      end
+    end
   end
 end

spec/click_house/response/factory_spec.rb

@@ -1,8 +1,60 @@
+# frozen_string_literal: true
+
 RSpec.describe ClickHouse::Response::Factory do
   subject do
     ClickHouse.connection
   end
 
+  describe '.response' do
+    let(:config) { ClickHouse::Config.new }
+    let(:faraday_env) { {} }
+    let(:summary_middleware) { instance_double(ClickHouse::Middleware::SummaryMiddleware) }
+
+    before do
+      allow(ClickHouse::Middleware::SummaryMiddleware).to receive(:extract).and_return(double('summary'))
+    end
+
+    context 'when response contains exception field' do
+      let(:faraday_response) do
+        double('Faraday::Response',
+               body: { 'exception' => 'Code: 46. DB::Exception: Unknown function' },
+               env: faraday_env)
+      end
+
+      it 'raises DbException' do
+        expect do
+          ClickHouse::Response::Factory.response(faraday_response, config)
+        end.to raise_error(ClickHouse::DbException, /Unknown function/)
+      end
+    end
+
+    context 'when response contains valid data' do
+      let(:faraday_response) do
+        double('Faraday::Response',
+               body: { 'meta' => [], 'data' => [] },
+               env: faraday_env)
+      end
+
+      it 'returns ResultSet' do
+        result = ClickHouse::Response::Factory.response(faraday_response, config)
+        expect(result).to be_a(ClickHouse::Response::ResultSet)
+      end
+    end
+
+    context 'when response is not a Hash' do
+      let(:faraday_response) do
+        double('Faraday::Response',
+               body: 'plain text response',
+               env: faraday_env)
+      end
+
+      it 'returns raw ResultSet' do
+        result = ClickHouse::Response::Factory.response(faraday_response, config)
+        expect(result).to be_a(ClickHouse::Response::ResultSet)
+      end
+    end
+  end
+
   describe 'WITH totals modifier' do
     context 'when blank' do
       let(:response) do