1HTML::FormHandler::ManuUasle:r:ICnofnltHarTtiMibLou:nt:DeFedofrlPmaeHtrailnodnDl(oe3cr)u:m:eMnatnautailo:n:InflationDeflation(3)
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6 HTML::FormHandler::Manual::InflationDeflation - inflation and deflation
7 of field values
8
10 version 0.40068
11
13 Manual Index
14 How to inflate and deflate field values.
16 DESCRIPTION
18 When working with the various ways that data can be transformed, in and
19 out, the meaning of the terms 'inflate' and 'deflate' starts to feel
20 kind of slippery. The one constant is that values presented in an HTML
21 form must be in a string format, or presented with select elements or
22 checkboxes.
23 There are two general types of inflation/deflation provided by
25 FormHandler. The first, 'standard' type inflates values in order to
26 validate them, and deflates them in order to present them in string
27 format via HTML. The other ('DB') type takes values provided by
28 defaults (usually a DB row, or item, but could also be a field default
29 or an init_object) and munges the values coming in and changes them
30 back going out.
31 Standard inflation/deflation
33 The standard type of inflation/deflation is implemented by using some
34 of the following options for inflation:
35 inflate_method
37 transform (using 'apply')
38 ..and the following options for deflation:
40 deflate_method
42 deflation (field attribute)
43 When validation starts, the param input will be inflated by the inflate
45 method, allowing validation to be performed on the inflated object.
46 When the 'fif' fill-in-form value is returned for HTML generation, the
48 deflation is used to flatten the object, usually into a string format.
49 DB inflation/deflation
51 The 'DB' type of inflation/deflation uses 'inflate_default_method' for
52 inflation, and 'deflate_value_method' for deflation. Deflation could
53 also be handled by changing the value in one of the various validation
54 methods.
55 This type of inflation/deflation is, logically, just a different way of
57 providing data munging around the defaults (item/init_object/default)
58 and 'value' output. The same effect could be achieved by performing a
59 transformation outside of FormHandler - if you were handling the
60 database updates yourself. Since the DBIC model enables automatic
61 database updates, this kind of inflation/deflation makes that easier.
62 One circumstance in which this type of inflation/deflation is useful is
64 when there's a single field in the database row object which you want
65 to expand into a compound field in the form.
66 Attributes used in deflation/inflation
68 Inflation methods
69 The field 'input' comes from the params that are passed in from the
71 submission of the form, so the input will always be in string format if
72 it comes from an HTTP request. It's also possible to pass in params in
73 other formats, of course. Or the params could be pre-processed before
74 passing in to FormHandler.
75 You should not normally be changing the 'input' attribute of a field.
77 If you want the changed field value to be used when re-presenting the
78 form, such as when you're adopting a standard format for the field, you
79 should set "fif_from_value => 1".
80 There are three options for standard inflation, or transforming the
82 field's 'input' to the field's 'value':
83 inflate_method
85 Provide a method on the field which inflates the field 'input'
86 (from params):
87 has_field 'futility' => ( inflate_method => \&inflate_field );
89 sub inflate_field {
90 my ( $self, $value ) = @_;
91 ....
92 return $value;
93 }
94 transform
96 In a sequence of 'apply' actions, changes the format of the 'value'
97 that is being validated. This might be useful if there are some
98 validations that work on one format of the value, and some that
99 work on another.
100 set the value in validation methods
102 In a validate method, you can change the format of the value, with
103 $field->value(...);
104 Deflation methods
106 deflate_method
108 Most general purpose deflation method. Provide a coderef which is a
109 method on the field:
110 has_field => 'foo' => ( deflate_method => \&deflate_foo );
112 sub deflate_foo {
113 my ( $self, $value ) = @_; # $self is the 'foo' field
114 <perform conversion>
115 return $value;
116 }
117 deflation
119 This is a coderef that performs deflation.
120 has_field => 'bar' => ( deflation => sub { shift $value; ... return $value } );
122 set the value in validation methods
124 Just like for inflation, you can change the value in a validation
125 method; however, it won't be used for fill-in-form unless you set
126 the 'fif_from_value' flag to true.
127 fif_from_value
129 Normally the fill-in-form value will be the param value that was
131 submitted. If you want to change the format of the input when re-
132 presenting the form, you can set 'fif_from_value'.
133 deflate_to
135 Earlier versions of FormHandler provided a 'deflate_to' attribute which
137 allowed the deflation methods to be used for multiple, confusing
138 purposes. This flag has been removed, since it made the process hard to
139 understand and was mixing apples and oranges. The new
140 inflation/deflation methods can handle all of the previous situations.
141
143 FormHandler Contributors - see HTML::FormHandler
144
146 This software is copyright (c) 2017 by Gerda Shank.
147 This is free software; you can redistribute it and/or modify it under
149 the same terms as the Perl 5 programming language system itself.
150perl v5.30.1 HTML2:0:2F0o-r0m1H-a3n0dler::Manual::InflationDeflation(3)