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 26
26:     def columns
27:       return @columns if @columns
28:       if (pcs = probable_columns) && pcs.all?
29:         @columns = pcs
30:       else
31:         super
32:       end
33:     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 40
40:     def probable_columns
41:       if (cols = opts[:select]) && !cols.empty?
42:         cols.map{|c| probable_column_name(c)}
43:       elsif !opts[:join] && !opts[:with] && (from = opts[:from]) && from.length == 1 && (from = from.first)
44:         if from.is_a?(SQL::AliasedExpression)
45:           from = from.expression
46:         end
47:         
48:         case from
49:         when Dataset
50:           from.probable_columns
51:         when Symbol, SQL::Identifier, SQL::QualifiedIdentifier
52:           schemas = db.instance_variable_get(:@schemas)
53:           if schemas && (table = literal(from)) && (sch = Sequel.synchronize{schemas[table]})
54:             sch.map{|c,_| c}
55:           end
56:         end
57:       end
58:     end

[Validate]