Tangram::Expr(3p)

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