initial sketch of Clauses.pm

diff --git a/lib/SQL/Abstract/Clauses.pm b/lib/SQL/Abstract/Clauses.pm
new file mode 100644 (file)
index 0000000..be8bfa8
--- /dev/null
+++ b/lib/SQL/Abstract/Clauses.pm
@@ -0,0 +1,56 @@
+package SQL::Abstract::Clauses;
+
+use strict;
+use warnings;
+use mro 'c3';
+use base 'SQL::Abstract';
+
+sub new {
+  shift->next::method(@_)->register_defaults
+}
+
+sub register_defaults {
+  my ($self) = @_;
+  $self->{clauses_of}{select} = [ qw(select from where order_by) ];
+  $self->{expand}{select} = sub { shift->_expand_statement(@_) };
+  $self->{render}{select} = sub { shift->_render_statement(@_) };
+  $self->{expand_clause}{'select.select'} = '_expand_maybe_list_expr';
+  $self->{expand_clause}{'select.from'} = sub {
+    $_[0]->_expand_maybe_list_expr($_[1], -ident)
+  };
+  $self->{expand_clause}{'select.where'} = 'expand_expr';
+  $self->{expand_clause}{'select.order_by'} = '_expand_order_by';
+  return $self;
+}
+
+sub _expand_statement {
+  my ($self, $type, $args) = @_;
+  my $ec = $self->{expand_clause};
+  return +{
+    map +($_ => (do {
+      my $val = $args->{$_};
+      if (defined($val) and my $exp = $ec->{"${type}.$_"}) {
+        $self->$exp($val);
+      } else {
+        $val;
+      }
+    })), sort keys %$args
+  };
+}
+
+sub _render_statement {
+  my ($self, $type, $args) = @_;
+  my @parts;
+  foreach my $clause (@{$self->{clauses_of}{$type}}) {
+    next unless my $clause_expr = $args->{$clause};
+    my ($sql, @bind) = $self->render_expr($clause_expr);
+    next unless defined($sql) and length($sql);
+    push @parts, [
+      $self->_sqlcase(join ' ', split '_', $clause).' '.$sql,
+      @bind
+    ];
+  }
+  return $self->_join_parts(' ', @parts);
+}
+
+1;