ArelVisitorsToSql

ArelVisitorsToSql is a component of the Arel library used by Ruby on Rails to translate an abstract relational object tree into SQL text. Functioning as a visitor, it traverses Arel nodes and emits database-specific SQL fragments, assembling them into complete statements such as SELECT … FROM … WHERE …, including support for joins, grouping, ordering, and limiting. In typical Rails usage, ArelVisitorsToSql is invoked indirectly through Arel's query constructors and by ActiveRecord when a relation is converted to SQL. The implementation resides under the Arel::Visitors namespace, with the canonical class name Arel::Visitors::ToSql; different adapters can extend or override behavior to accommodate dialect specifics, quoting rules, and identifier escaping. As a dialect-aware emitter, it relies on the current database adapter to produce correct syntax for the target database (PostgreSQL, MySQL, SQLite, etc.). The visitor pattern used by Arel separates the concerns of building a query (the AST) from rendering SQL, improving portability across databases and enabling chaining of query methods. While application developers typically interact with Arel through higher-level ActiveRecord query methods, understanding the ToSql visitor provides insight into how Arel converts abstract queries into concrete SQL strings.