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 30
30:     def columns
31:       if cols = _columns
32:         return cols
33:       end
34:       if (pcs = probable_columns) && pcs.all?
35:         self.columns = pcs
36:       else
37:         super
38:       end
39:     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 46
46:     def probable_columns
47:       if (cols = opts[:select]) && !cols.empty?
48:         cols.map{|c| probable_column_name(c)}
49:       elsif !opts[:join] && !opts[:with] && (from = opts[:from]) && from.length == 1 && (from = from.first)
50:         if from.is_a?(SQL::AliasedExpression)
51:           from = from.expression
52:         end
53:         
54:         case from
55:         when Dataset
56:           from.probable_columns
57:         when Symbol, SQL::Identifier, SQL::QualifiedIdentifier
58:           schemas = db.instance_variable_get(:@schemas)
59:           if schemas && (table = literal(from)) && (sch = Sequel.synchronize{schemas[table]})
60:             sch.map{|c,_| c}
61:           end
62:         end
63:       end
64:     end

[Validate]