Specifications in Go: Composable Query Predicates Without an ORM Leak

The code you've provided outlines an elegant way to translate complex query specifications (expressions) into SQL queries in Go. This approach separates the logic of constructing a query from its execution, ensuring that your domain-specific language for querying remains clean and testable.

Key Components

1. Query Specifications:

   • The spec package contains types representing different parts of a query specification.
   • These include leaf nodes (e.g., and, or, not) and composite nodes (e.g., andSQL, orSQL, notSQL).

2. Translation to SQL:

   • Each node type implements the ToSQL method, which recursively translates itself into a SQL string.
   • The ToSQL methods for composite types (andSQL, orSQL, notSQL) call their children's ToSQL methods and wrap them in appropriate SQL syntax.

3. Execution:

   • The IsSatisfiedBy method is used to check if a given query specification matches a specific input (e.g., for testing purposes).
   • For actual database queries, the translator would generate the SQL string and pass it along with parameters to an ORM or raw

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