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.\" ========================================================================
.\"
.IX Title "Tangram::Relational 3pm"
.TH Tangram::Relational 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.
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.nh
.SH "NAME"
Tangram::Relational \- Orthogonal Object Persistence in Relational Databases
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&   use Tangram;
\&
\&   $schema = Tangram::Relational\->schema( $hashref );
\&
\&   Tangram::Relational\->deploy($schema, $dbh);
\&
\&   $storage = Tangram::Relational\->connect( $schema,
\&      $data_source, $username, $password );
\&
\&   $storage\->disconnect();
\&
\&   Tangram::Relational\->retreat($schema, $dbh);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This is the entry point in the vanilla object-relational persistence
backend. Vendor-specific backends should be used when they
exist. Currently Mysql, Sybase and Oracle have such backends; see
Tangram::mysql, Tangram::Sybase and Tangram::Oracle.
.PP
More backends could be added in the future; they might implement
persistence in \s-1XML\s0 documents, pure object databases, using C database
libraries to bypass the need for an \s-1RDBMS,\s0 etc.
.SH "CLASS METHODS"
.IX Header "CLASS METHODS"
.SS "schema"
.IX Subsection "schema"
.Vb 1
\&   $schema = Tangram::Relational\->schema( $hashref );
.Ve
.PP
Returns a new Schema object. See Tangram::Schema.
.SS "deploy"
.IX Subsection "deploy"
.Vb 3
\&   Tangram::Relational\->deploy($schema);
\&   Tangram::Relational\->deploy($schema, HANDLE);
\&   Tangram::Relational\->deploy($schema, @dbi_args);
.Ve
.PP
Writes \s-1SQL\s0 statements for preparing a database for use with the given
\&\f(CW$schema\fR.
.PP
Called with a single argument, writes \s-1SQL\s0 statements to \s-1STDOUT.\s0
.PP
Called with two arguments, writes \s-1SQL\s0 statements to \s-1HANDLE. HANDLE\s0 may
be a \s-1DBI\s0 connection handle or a file handle.
.PP
Called with more than two arguments, passes all but the first to
\&\fBDBI::connect()\fR and writes statements to the resulting \s-1DBI\s0 handle,
which is automatically closed.
.PP
The \s-1SQL\s0 code is only guaranteed to work on newly created databases.
.SS "connect"
.IX Subsection "connect"
.Vb 2
\&   $storage = Tangram::Relational\->connect( $schema,
\&      $data_source, $user, $password, \e%options )
.Ve
.PP
Connects to a storage and return a handle object. Dies in case of
failure.
.PP
\&\f(CW$schema\fR is a Schema object describing the system of
classes stored in the database.
.PP
\&\f(CW$data_source\fR, \f(CW$user\fR and \f(CW$password\fR are passed directly to
\&\fBDBI::connect()\fR.
.PP
\&\e%options is a reference to a hash containing connection options. See
Tangram::Storage for a description of available options.
.SS "retreat"
.IX Subsection "retreat"
.Vb 3
\&   Tangram::Relational\->retreat($schema);
\&   Tangram::Relational\->retreat($schema, HANDLE);
\&   Tangram::Relational\->retreat($schema, @dbi_args);
.Ve
.PP
Remove the tables created by \fBdeploy()\fR. Only guaranteed to work against
a database that was deployed using exactly the same schema.
.PP
For an explanation of the possible argument lists, see deploy.
.SH "WRITING A VENDOR DRIVER"
.IX Header "WRITING A VENDOR DRIVER"
Like Charles Moore (inventor of Forth) used to say, \*(L"standards are
great, everybody should have one!\*(R".
.PP
Tangram can take advantage of extensions available in some \s-1SQL\s0
dialects.
.PP
To create a vendor-specific driver, call it \f(CW\*(C`Tangram::Foo\*(C'\fR (where
\&\f(CW\*(C`Foo\*(C'\fR is the name of the \s-1DBI\s0 driver, as would be selected with the
\&\s-1DBI\s0 connection string \f(CW\*(C`dbi:Foo:\*(C'\fR), and derive \f(CW\*(C`Tangram::Relational\*(C'\fR.
.PP
For now, the existing back-ends should be used as examples of how to
extend Tangram to support different databases or utilise some of their
more exotic features.