# PODNAME: Yancy::Guides::Schema
# ABSTRACT: How to connect to and describe your schema

__END__

=pod

=head1 NAME

Yancy::Guides::Schema - How to connect to and describe your schema

=head1 VERSION

version 1.072

=head1 SYNOPSIS

    use Mojolicious::Lite;
    plugin Yancy => {
        backend => 'pg://localhost/myapp',
        read_schema => 1,
        schema => {
            users => {
                title => 'Users',
                description => 'The authorized user accounts',
            },
        },
    };

=head1 DESCRIPTION

This document describes how to configure a database connection (Backend)
and how to add annotations to your schema.

=head1 Database Backend

The C<backend> URL defines what database to use and how to connect to
it. Each backend has its own format of URL, and some examples are shown
below. See your backend's documentation for more information.

=over

=item L<Postgres backend|Yancy::Backend::Pg>

    # Backend URL
    backend => 'pg://user@example.com/mydb',

    # Backend hash
    backend => {
        Pg => {
            dsn => 'dbi:Pg:dbname',
            username => 'fry',
            password => 'b3nd3r1sgr34t',
        },
    }

=item L<MySQL backend|Yancy::Backend::Mysql>

    # Backend URL
    backend => 'mysql://user@localhost/mydb',

    # Backend hash
    backend => {
        Mysql => {
            dsn => 'dbi:mysql:mydb',
            username => 'fry',
            password => 'b3nd3r1sgr34t',
        },
    }

=item L<SQLite backend|Yancy::Backend::Sqlite>

    # Backend URL
    backend => 'sqlite:filename.db',

    # Backend hash
    backend => {
        Sqlite => {
            dsn => 'sqlite:data.db',
        },
    }

=item L<DBIx::Class backend|Yancy::Backend::Dbic>

    # Backend URL
    backend => 'dbic://My::Schema/dbi:SQLite:file.db',

    # Backend arrayref (passed to Schema->connect() method)
    backend => {
        Dbic => [
            'My::Schema',
            'dbi:SQLite:mysql.db',
            undef, undef,
            { PrintError => 1 },
        ],
    }

=back

=head1 Schema

The C<schema> data structure defines what data is in the database.
Each key in this structure refers to the name of a schema, and the
value describe the fields for items inside the schema.

Each backend may define a schema differently. For a relational
database like Postgres or MySQL, a schema is a table, and the fields
are columns. For an ORM like DBIx::Class, the schemas are ResultSet
objects. For a document store like MongoDB, the schemas are
collections. See your backend's documentation for more information.

Schemas are configured using L<JSON Schema|http://json-schema.org>.
The JSON Schema defines what fields (properties) an item has, and what
type of data those field have. The JSON Schema also can define
constraints like required fields or validate strings with regular
expressions. The schema can also contain metadata like a C<title>,
C<description>, and even an C<example> value. For more information on
what can be defined, see L<the docs on JSON Schema|http://json-schema.org>.

For a schema named C<people> that has 3 fields (an integer C<id> and
two strings, C<name> and C<email>), a minimal JSON schema will look like
this:

    schema => {
        people => {
            properties => {
                id => {
                    type => 'integer',
                    readOnly => 1,
                },
                name => {
                    type => 'string',
                },
                email => {
                    type => 'string',
                },
            },
        },
    },

By default, Yancy will read your database to fill in as much schema
information as it can. This includes the field C<type>, field order
(C<x-order>), enumerated values (C<enum>), required fields
(C<required>), ID fields (C<x-id-field>), foreign keys
(C<x-foreign-key>), and some C<format> (date/time mostly). You can (and
should) add your own annotations and corrections while configuring
Yancy. The C<schema> configuration will be merged with the information
Yancy reads from the database, with the configuration overriding
the defaults from the database.

=head2 Types

Yancy generates input elements based on the C<type>, and C<format> of
the object's properties.

=over

=item * C<< type => "boolean" >> - A Yes/No field.  Boolean fields
support input values C<0>, C<1>, C<"true">, and C<"false">. They will be
stored as C<0>, and C<1> in the database.

=item * C<< type => "integer" >> - A number field (C<< <input type="number" > >>)

=item * C<< type => "number" >> - A number field (C<< <input type="number" > >>)

=item * C<< type => "string", format => "date" >> - A date field (C<< <input type="date"> >>)

=item * C<< type => "string", format => "date-time" >> - A date/time field (C<< <input type="datetime-local"> >>)
Date/time fields can have a special C<default> value: C<now>. This will
be replaced with the current date/time in the database.

=item * C<< type => "string", format => "email" >> - A e-mail address (C<< <input type="email"> >>)

=item * C<< type => "string", format => "url" >> - A URL input (C<< <input type="url"> >>)

=item * C<< type => "string", format => "tel" >> - A telephone number (C<< <input type="tel"> >>)

=item * C<< type => "string", format => "textarea" >> - A multiline text field (C<< <textarea> >>)

=item * C<< type => "string", format => "markdown" >> - A Markdown field
that shows a live preview of the rendered HTML. The Markdown can be
saved as HTML in another field by adding C<< x-html-field => $field_name >>
to that field.

=item * C<< enum => [...], type => "..." >> - A C<< <select> >> element.
This can be of any type.

=item * C<< type => "string", format => "filepath" >> - A file upload
field (C<< <input type="file"> >>). See L<Yancy::Plugin::File> for more
information.

=item * C<< type => "string", format => "binary" >> - A field containing binary data.
This currently does not generate any input field, but it may become
another way to upload files in the future.

=back

JSON schemas allow specifying multiple types for a field using an array.
If a field has multiple types, the generated form will use the first
type to decide what kind of field to display.

=head2 Field Configuration

Other schema attributes will be translated as necessary to the HTML
input fields:

=over

=item * C<title> will be used to label the input field

=item * C<description> will be placed near the input field to explain it

=item * C<readOnly> will set the input field as read-only

=item * C<pattern> for string fields, a string that can be used as a regex, like C<< pattern => '^foo-\d+$' >>.

=item * C<minimum> for numeric fields, the minimum value

=item * C<maximum> for numeric fields, the maximum value

=item * C<minLength> for string fields, the minimum length

=item * C<maxLength> for string fields, the maximum length

=back

=head2 Required Values

JSON Schema allows marking properties as required using the C<required>
property, which must be an array of property names.

    schema => {
        people => {
            required => [ 'name', 'email' ],
            properties => {
                id => {
                    type => 'integer',
                    readOnly => 1,
                },
                name => {
                    type => 'string',
                },
                email => {
                    type => 'string',
                },
            },
        },
    },

Required values will be marked as such in the HTML.

=head2 Nullable Values

If a value can be C<null> (C<undef> in Perl terms) in addition to its
declared type (C<string>, C<integer>, etc...), you must add it to the
C<type> field by using an array of types:

    schema => {
        people => {
            required => [ 'name' ],
            properties => {
                id => {
                    type => 'integer',
                    readOnly => 1,
                },
                name => {
                    type => 'string', # Required and must be a string
                },
                email => {
                    type => [ 'string', 'null' ], # Can be null
                },
            },
        },
    },

If you don't do this, and still include the field in an object, you will
get an error: C<Expected string - Got null.>. The correct way to fix
this error is to add C<null> as an option for the field's type.

=head2 Extended Collection Configuration

There are some extended fields you can add to your schema definition
to control how it is treated by Yancy.

=over

=item title

A friendly title for the schema

=item description

A description of the schema. Markdown will be parsed into HTML.

You can use the C<trim> and C<unindent> functions from L<Mojo::Util> to
allow indenting your schema description:

    use Mojolicious::Lite;
    use Mojo::Util qw( unindent trim );
    plugin Yancy => {
        schema => {
            employees => {
                description => unindent( trim q{
                    The employees of Planet Express.

                    * [View the employee health plan](/decapod-life)
                    * [Latest Good News](/news)
                } ),
            },
        },
    };

=item x-hidden

If this is true, the schema will be hidden from the list in the Yancy
web app. This does not prevent using the API to edit this data.

=item x-ignore

Ignore this schema: Do not add it to the API, do not show it in the
rich editing form. This is for schema that should not be edited
from the Yancy form or the Yancy API.

This allows for removing schema when using L</read_schema>.

=item x-id-field

This key sets the name of the schema's ID field to use to uniquely
identify individual items. By default, Yancy assumes the ID field is
named C<id>. If your schema uses some other identifier (e-mail
address or username for example), you should set this configuration key.

    people => {
        'x-id-field' => 'email',
        properties => { ... },
    },

This field can be any unique identifier, but it will be the ID that
Yancy uses for all of its operations.

=item x-list-columns

This key should be an array of columns to display on the list view, in
order. This helps put useful information on the list page.

    people => {
        'x-list-columns' => [ 'name', 'email' ],
        properties => { ... },
    },

Instead of field names, columns can also be made out of templates using
a hash with C<title> and C<template> keys. Inside the template key, use
fields from the row with C<{field}>, like so:

    people => {
        'x-list-columns' => [
            { title => "Person", template => '{name} <{email}>' },
        ],
    },

=item x-filter

This key is an array of filter names to run when setting or creating an
item. Filters can allow for hashing passwords, for example.  Filters are
added by plugins or during configuration of
L<Mojolicious::Plugin::Yancy>. See
L<Mojolicious::Plugin::Yancy/yancy.filter.add> for how to create
a filter in your app.

Instead of a filter name, you can provide an array. The first member
will be the name, and any further members will be passed to the filter
code-ref as parameters after the mandatory three.

=item x-view-url

A URL to view the schema in the application. Will be shown as a button
in the editor.

=item x-view-item-url

A URL to view the items in the schema. Will be shown as an icon next to
the item row. Add data from the row in the url using C<{field}>, like so:

    # /people/1
    /people/{id}
    # /user/preaction
    /user/{username}

=back

=head2 Extended Field Configuration

There are some extended fields you can add to a field configuration
to control how it is treated by Yancy.

=over

=item title

A friendly title for the field

=item description

A description of the field. Markdown will be parsed into HTML.

=item default

The default value for the field, if the field is missing or C<undef>
(C<null> in JavaScript).

=item x-foreign-key

If provided, this field is a foreign key linking to the given schema.
This field must link to the ID field of the other schema.

    schema => {
        user => {
            'x-id-field' => 'username',
            properties => {
                username => {
                    type => 'string',
                },
            },
        },
        comment => {
            properties => {
                username => {
                    type => 'string',
                    'x-foreign-key' => 'user',
                },
            },
        },
    },

By default, the target schema's first list column (if C<x-list-columns>
is defined) or the schema's ID field is used to show the current value
of the relationship. This can be changed by setting C<x-display-field> to
the field in the target schema you want to use.

By default, the target schema's ID field (C<x-id-field> or C<id>) will
be used as the value for the foreign key. This can be changed by setting
C<x-value-field> to the field in the target schema you want to use.

B<NOTE:> This support is experimental and will need further development
to support more possibilities of foreign key linkages. Patches
appreciated!

=item x-hidden

If true, thie field will be hidden from the rich editing form. This is
for schema that you want to use from the API but do not want to
edit from the Yancy application.

=item x-order

Set the order of the fields in the edit form by assigning a number to
the C<x-order> property. Fields in the form are be sorted by their
C<x-order>, and then by their name (alphabetically). Fields that do not
have C<x-order> set will be sorted after fields that do.

=item x-filter

This key is an array of filter names to run on the field when setting or
creating an item. Filters can allow for hashing passwords, for example.
Filters are added by plugins or during configuration of
L<Mojolicious::Plugin::Yancy>. See
L<Mojolicious::Plugin::Yancy/yancy.filter.add> for how to create a filter
in your app.

Instead of a filter name, you can provide an array. The first member
will be the name, and any further members will be passed to the filter
code-ref as parameters after the mandatory three.

=item x-view

    # to get a data-light "view" of users when listing comments end of blogpost
    usermini => {
        type => 'object',
        'x-view' => { schema => 'user' },
        properties => {
            id => { 'x-order' => 1, type => 'integer' },
            username => { 'x-order' => 2, type => 'string' },
        },
    },

This key means the schema is not a real one that exists in the
backend, but a strict subset of a real one. It is an object with keys:

=over

=item schema

Mandatory. Names the "real" schema. B<NB> This is the schema's
text name, not a JSON pointer.

=back

All the properties' types will need to be the same as on the "real"
one since the datasource will be the real one. If no properties are given,
the "real" schema's ones will be used.

The generated OpenAPI spec will only have read functionality for the
"view" schema, not mutations.

=back

=head1 SEE ALSO

L<Yancy>, L<Mojolicious::Plugin::Yancy>

=head1 AUTHOR

Doug Bell <preaction@cpan.org>

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2021 by Doug Bell.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut
