NAME

       Tangram::Expr - represent expressions on database server side

SYNOPSIS

          my ($r1, $r2) = $storage->remote(qw( ... ));

          $r1->{field} operator $value
          $r1->{field} operator $r2->{field2}

          $r1->{collection}->includes( $obj )
          $r1->{collection}->exists( $obj, $filter )
          $r1->{collection}->includes_or( $obj1, $obj2, ... )

DESCRIPTION

       Tangram::Expr objects represent expressions that will be evaluated on the database server side.

       Expression objects fall into one of the following categories: numeric, string, reference or collection.

       Many of the methods in Expr are needed only by people extending Tangram.  See also Tangram::Relational,
       and the source the Tangram::mysql and Tangram::Sybase for examples on how these functions are intercepted
       to allow RDBMS-specific expressions.

NUMERIC EXPRESSIONS

       Numeric expression objects can be compared using the operators ==, !=, <, >, <= and >=.  The other
       operand must be either another numeric expression object, or a normal Perl numeric value.  The result of
       the comparison is a Filter.

STRING EXPRESSIONS

       String expression objects can be compared using the operators eq, ne, lt, gt, le, and ge.  The other
       operand must be either a string expression object or any Perl scalar value. Tangram will automatically
       quote the operand as required by the SQL syntax.  The result of the comparison is a
       Tangram::Expr::Filter.

       String expression objects also support the method like($str), where $str is a string that may contain SQL
       wildcards. The result is a Tangram::Expr::Filter that translates to a SQL "LIKE $str" predicate.

REFERENCE EXPRESSIONS

       Reference expression objects can be compared for equality using operators == and !=. The other operand
       must be another reference expression, a persistent object or undef(). The result of the comparison is a
       Filter.

COLLECTION EXPRESSIONS

       Collection expression objects represents a collection inside an object. It supports the includes() and
       exists() methods, which returns a Tangram::Expr::Filter stating that the collection must contain the
       operand. exists() uses a subselect.

       It also supports the includes_or() methods, which accepts a list and is performs a logical OR - using the
       IN (x,y,z) SQL construct.

       The operand may be a Tangram::Remote, a persistent object, or an object ID.

       operator < is provided as a synonym for includes().

       The includes() method can be used for all collection types (Set, Array, Hash, and the Intr* versions).

PREDICATES

       Predicate objects represent logical expressions, or conditions. Predicates support logical operators &, |
       and !. Note that a single ampersand or vertical bar must be used (this is a Perl limitation).  The result
       is another predicate.

CLASS METHODS

   new($type, $expr, @remotes)
       Returns a new instance.

       $type is a Type object corresponding to this expression (see Tangram::Type).

       $expr is a SQL expression. It will eventually become part of a WHERE-CLAUSE.

       @remotes contains the Remote objects (see Tangram::Remote) that participate in the expression. Tangram
       uses this list to insert the corresponding tables in the FROM clause and conditions in the WHERE-CLAUSE.

INSTANCE METHODS

   expr()
       Returns the SQL equivalent for this expression.

   type()
       Returns the Type (see Tangram::Type) corresponding  to this expression.

   objects()
       Returns the list of the objects that participate in this expression.

   storage()
       Returns the Storage associated with this expression.

EXAMPLES

       $person is called 'Homer'

             $person->{name} eq 'Homer'

       $person's name ends with 'mer'

             $person->{name}->like('%mer');

       $person is older than 35

             $person->{age} > 35

       $person is married to $homer

             $person->{partner} == $homer

       $person is not $homer

             $person != $homer

       $person is not $homer and is older than 65

             $person != $homer & $person->{age} > 65

       $person is $bart's parent

             $person->{children}->includes( $bart )
             $person->{children} < $bart

       $person is not $bart's parent

             !$person->{children}->includes( $bart )
             !($person->{children} < $bart)

       $person is one of the local list of people, @person

             $person->in(@person)

SEE ALSO

       Tangram::Remote, Tangram::Expr, Tangram::Storage