Module Sequel::ColumnsIntrospection
In: lib/sequel/extensions/columns_introspection.rb

Methods

Public Instance methods

Attempt to guess the columns that will be returned if there are columns selected, in order to skip a database query to retrieve the columns. This should work with Symbols, SQL::Identifiers, SQL::QualifiedIdentifiers, and SQL::AliasedExpressions.

[Source]

    # File lib/sequel/extensions/columns_introspection.rb, line 30
30:     def columns
31:       return @columns if @columns
32:       if (pcs = probable_columns) && pcs.all?
33:         self.columns = pcs
34:       else
35:         super
36:       end
37:     end

Protected Instance methods

Return an array of probable column names for the dataset, or nil if it is not possible to determine that through introspection.

[Source]

    # File lib/sequel/extensions/columns_introspection.rb, line 44
44:     def probable_columns
45:       if (cols = opts[:select]) && !cols.empty?
46:         cols.map{|c| probable_column_name(c)}
47:       elsif !opts[:join] && !opts[:with] && (from = opts[:from]) && from.length == 1 && (from = from.first)
48:         if from.is_a?(SQL::AliasedExpression)
49:           from = from.expression
50:         end
51:         
52:         case from
53:         when Dataset
54:           from.probable_columns
55:         when Symbol, SQL::Identifier, SQL::QualifiedIdentifier
56:           schemas = db.instance_variable_get(:@schemas)
57:           if schemas && (table = literal(from)) && (sch = Sequel.synchronize{schemas[table]})
58:             sch.map{|c,_| c}
59:           end
60:         end
61:       end
62:     end

[Validate]