module Sequel::ColumnsIntrospection
Public Instance Methods
columns()
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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.
Calls superclass method
# File lib/sequel/extensions/columns_introspection.rb, line 30 def columns if cols = _columns return cols end if (pcs = probable_columns) && pcs.all? self.columns = pcs else super end end
Protected Instance Methods
probable_columns()
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Return an array of probable column names for the dataset, or nil if it is not possible to determine that through introspection.
# File lib/sequel/extensions/columns_introspection.rb, line 46 def probable_columns if (cols = opts[:select]) && !cols.empty? cols.map{|c| probable_column_name(c)} elsif !opts[:join] && !opts[:with] && (from = opts[:from]) && from.length == 1 && (from = from.first) if from.is_a?(SQL::AliasedExpression) from = from.expression end case from when Dataset from.probable_columns when Symbol, SQL::Identifier, SQL::QualifiedIdentifier schemas = db.instance_variable_get(:@schemas) if schemas && (table = literal(from)) && (sch = Sequel.synchronize{schemas[table]}) sch.map{|c,_| c} end end end end
Private Instance Methods
probable_column_name(c)
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Return the probable name of the column, or nil if one cannot be determined.
# File lib/sequel/extensions/columns_introspection.rb, line 70 def probable_column_name(c) case c when Symbol _, c, a = split_symbol(c) (a || c).to_sym when SQL::Identifier c.value.to_sym when SQL::QualifiedIdentifier col = c.column col.is_a?(SQL::Identifier) ? col.value.to_sym : col.to_sym when SQL::AliasedExpression a = c.alias a.is_a?(SQL::Identifier) ? a.value.to_sym : a.to_sym end end