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

Methods

columns   probable_columns  

Public Instance methods

columns()

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 25
25:     def columns
26:       return @columns if @columns
27:       if (pcs = probable_columns) && pcs.all?
28:         @columns = pcs
29:       else
30:         columns_without_introspection
31:       end
32:     end

Protected Instance methods

probable_columns()

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 39
39:     def probable_columns
40:       if (cols = opts[:select]) && !cols.empty?
41:         cols.map{|c| probable_column_name(c)}
42:       elsif !opts[:join] && !opts[:with] && (from = opts[:from]) && from.length == 1 && (from = from.first)
43:         if from.is_a?(SQL::AliasedExpression)
44:           from = from.expression
45:         end
46:         
47:         case from
48:         when Dataset
49:           from.probable_columns
50:         when Symbol, SQL::Identifier, SQL::QualifiedIdentifier
51:           schemas = db.instance_variable_get(:@schemas)
52:           if schemas && (sch = Sequel.synchronize{schemas[literal(from)]})
53:             sch.map{|c,_| c}
54:           end
55:         end
56:       end
57:     end

[Validate]