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.\" ========================================================================
.\"
.IX Title "Tangram::Type::Array::FromOne 3pm"
.TH Tangram::Type::Array::FromOne 3pm "2022-10-16" "perl v5.34.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Tangram::Type::Array::FromOne \- map Perl arrays using a foreign key
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&   use Tangram;
\&
\&   # or
\&   use Tangram::Core;
\&   use Tangram::Type::Array::FromOne;
\&
\&   $schema = Tangram::Schema\->new(
\&
\&      classes => { Agenda => { fields => {
\&
\&      iarray =>
\&      {
\&         # long form
\&         entries =>
\&         {
\&            class => \*(AqEntry\*(Aq,
\&            coll => \*(Aqagenda\*(Aq,
\&         },
\&
\&         # or (short form)
\&         entries => \*(AqEntry\*(Aq,
\&      }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This class maps references to a Perl array in an intrusive
fashion. The persistent fields are grouped in a hash under the
\&\f(CW\*(C`iarray\*(C'\fR key in the field hash.
.PP
The array may contain only objects of persistent classes. These classes
must have a common persistent base class.
.PP
Tangram uses two columns on the element's table to store:
.IP "\(bu" 4
the id of the object containing the collection
.IP "\(bu" 4
the position of the element in the collection
.PP
\&\s-1CAUTION:\s0 the same object may not be an element of the same collection,
in two different objects. This mapping may be used only for
one-to-many relationships.
.PP
The field names are passed in a hash that associates a field name with
a field descriptor. The field descriptor may be either a hash or a
string. The hash uses the following fields:
.IP "\(bu" 4
class
.IP "\(bu" 4
aggreg
.IP "\(bu" 4
back
.IP "\(bu" 4
coll
.IP "\(bu" 4
slot
.IP "\(bu" 4
deep_update
.PP
Mandatory field \f(CW\*(C`class\*(C'\fR specifies the class of the elements.
.PP
Optional field \f(CW\*(C`aggreg\*(C'\fR specifies that the elements of the collection
must be removed (erased) from persistent storage along with the
containing object. The default is not to aggregate.
.PP
Optional field \f(CW\*(C`back\*(C'\fR sets the name of a field that is inserted in
the elements. That field acts as a demand-loaded, read-only reference
to the object containing the collection.
.PP
Optional field \f(CW\*(C`coll\*(C'\fR sets the name the column containing the id of
the containing object. This defaults to 'C_m', where 'C' is the class
of the containing object, and 'm' is the field name.
.PP
Optional field \f(CW\*(C`slot\*(C'\fR sets the name the column containing the id of
the containing object. This defaults to 'C_m_slot', where 'C' is the
class of the containing object, and 'm' is the field name.
.PP
The \*(L"C\*(R" in C_m and C_m_slot are passed through the schema
normalisation function before being combined into a column name.
.PP
Optional field \f(CW\*(C`deep_update\*(C'\fR specificies that all elements have to be
updated automatically when \f(CW\*(C`update\*(C'\fR is called on the collection
object. Automatic update ensures consisitency between the Perl
representation and the \s-1DBMS\s0 state, but degrades update performance so
use it with caution. The default is not to do automatic updates.
.PP
If the descriptor is a string, it is interpreted as the name of the
element's class. This is equivalent to specifying only the \f(CW\*(C`class\*(C'\fR
field in the hash variant.