Docs: Add Rails console testing section to QueryRecorder documentation

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Problem to solve

  • What product or feature(s) affected? QueryRecorder tool for N+1 query detection
  • What docs or doc section affected? doc/development/database/query_recorder.md
  • Is there a problem with a specific document, or a feature/process that's not addressed sufficiently in docs? The current documentation focuses on using QueryRecorder in tests but doesn't explain how developers can use it interactively in the Rails console during development to analyze query counts before writing tests.

Further details

  • What concepts, procedures, reference info we could add? Add practical examples showing how to use QueryRecorder in the Rails console to count and compare queries for different ActiveRecord loading strategies (preload, includes, etc.)
  • Use cases and benefits:
    • Helps developers debug N+1 queries during feature development
    • Allows quick comparison of different preloading strategies without writing tests
    • Enables validation of query optimizations before committing code
    • Provides immediate feedback on query performance during development
  • Intended audience: Backend developers working on database query optimization, particularly those dealing with N+1 query issues (personas: Backend Engineer, Database Specialist)

Proposal

Add a new section "Testing query counts in the Rails console" to the QueryRecorder documentation that includes:

## Testing query counts in the Rails console

During development, it can be challenging to identify and count database queries directly in the Rails console output. The QueryRecorder can be used interactively to help analyze and optimize query performance before writing tests.

This is particularly useful when:
- Debugging N+1 queries during feature development
- Comparing different preloading strategies
- Validating query optimizations before committing code

The QueryRecorder helper is not automatically loaded in the Rails console, so you must require it first:

```ruby
# Important: Require the QueryRecorder helper (not loaded by default)
require './spec/support/helpers/query_recorder.rb'

# Example: Analyzing query counts for different preloading strategies
result = {}
package_files = Packages::PackageFile.limit(5)

# Create a helper to count queries
query_counter = proc do |&query_block|
ActiveRecord::QueryRecorder.new(&query_block).data.map { |_, v| v[:count] }.reduce(&:+)
end

# Test different approaches
result['without preloading'] = query_counter.call { package_files.map(&:package) }
result['with preload(:package)'] = query_counter.call { package_files.preload(:package).map(&:package) }
result['with includes(package: :project)'] = query_counter.call { package_files.includes(package: :project).map(&:package) }

# View results
result
# => {"without preloading"=>5, "with preload(:package)"=>2, "with includes(package: :project)"=>2}

# Find the most efficient approach
result.min { |a, b| a.second <=> b.second }
# => ["with preload(:package)", 2]
```

This approach allows you to quickly test and compare different query strategies during development, helping you choose the most efficient implementation before writing your tests and code.

Who can address the issue

Any backend developer familiar with QueryRecorder and ActiveRecord query optimization. No special expertise required beyond understanding Rails database queries.

Other links/references

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