Module: Exwiw::QueryAst

Defined in:
lib/exwiw/query_ast.rb

Defined Under Namespace

Modules: ColumnValue Classes: JoinClause, Select, SelectSubquery, Subquery, UnionSubquery, WhereClause

Class Method Summary collapse

Class Method Details

.reads_table?(query, table_name) ⇒ Boolean

Whether query (a Select) reads table_name anywhere — as its FROM, as a join, or inside a nested scope subquery. Used to detect the two shapes a self-referencing scope subquery creates: a polymorphic arm whose target is scoped through the very table the arms belong to (QueryAstBuilder), and a DELETE whose subquery reads the table being deleted from, which MySQL rejects outright (MysqlAdapter).

Returns:

  • (Boolean) 


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# File 'lib/exwiw/query_ast.rb', line 11

def self.reads_table?(query, table_name)
  return true if query.from_table_name == table_name
  return true if query.join_clauses.any? { |j| j.join_table_name == table_name || j.base_table_name == table_name }

  query.where_clauses.any? do |where_clause|
    next false unless where_clause.is_a?(WhereClause)

    case where_clause.value
    when SelectSubquery
      reads_table?(where_clause.value.query, table_name)
    when UnionSubquery
      where_clause.value.queries.any? { |q| reads_table?(q, table_name) }
    else
      false
    end
  end
end